Self Help

How Life Works A User’s Guide to the New Biology - Philip Ball

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Matheus Puppe

· 98 min read

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Here is a summary of the key points from the introduction to How Life Works:

  • When the human genome was first sequenced in 2000, it was commonly referred to as the “language of God” or the “instruction book of life.” This implied the genome contained a detailed set of instructions or coding that controlled how life works.

  • However, two decades of research since then have shown that understanding life through the genome is far more complex than anticipated. The genome alone does not provide a clear explanation of how organisms develop and function.

  • Misleading metaphors like the “genome as instruction book” persist because the real biological mechanisms are complicated. But alternative views that have emerged paint a richer picture.

  • Research shows life works through principles of self-organization and emergence, rather than tight genetic control. Genes act as servants that allow robust, flexible systems to develop, not as dictators prescribing every response.

  • Organisms seem to increasingly relinquish direct genetic control as complexity increases, instead providing the ingredients for adaptive, improvised solutions.

  • The new understanding dispels the view of living things as machines. Cells work in ways no machine does, through non-deterministic, self-organizing processes rather than programming.

  • While much remains to be uncovered, this new view offers a more accurate picture of how life really works compared to the simplistic metaphors stemming from the initial genome sequencing era.

The author argues that viewing biological systems as analogous to machines or computers is flawed and has limited our understanding of life. While comparing living things to human technologies can sometimes provide useful metaphors, cells and biological processes work fundamentally differently than any engineered system.

The key distinction is that life operates based on principles of emergence, hierarchy, noise and unpredictability rather than precise engineering. Biological functions emerge from complex organizational structures across multiple scales, from molecules to organisms. Life thrives on randomness and fluctuations rather than precisely maintaining order.

To illustrate this, the author discusses a thought experiment where biologists try to understand a transistor radio the way they typically study biology - by dissecting and categorizing its parts without understanding the overall operational logic. This approach fails to reveal how the radio works and cannot fix it.

The lesson is that biology requires developing a new way of thinking beyond just analyzing parts and connections. The “logic” of life is different and we need new conceptual frameworks to truly comprehend living systems, not just better engineering languages. Defining life may lie not in its components but in its ability to generate meaning and adapt based on principles we are just beginning to discern.

  • Medicine has traditionally tried to study and treat diseases one by one, but a more holistic view is needed that recognizes diseases often affect the body through similar mechanisms.

  • Life can be redesigned at multiple levels - genetically through tools like CRISPR, but also by reprogramming cells and engineering living systems and tissues rather than just modifying genes alone.

  • Modern biology has generated huge amounts of data but more understanding is still needed of the underlying principles and explanations for how life works rather than just descriptions from data mining.

  • Key principles that will help guide understanding include complexity/redundancy, modularity, robustness, canalization, and multilevel hierarchical organization. Life is highly complex but functional outcomes are limited by canalization into a small number of states. Modularity, redundancy and other features provide robustness against disruption.

In summary, it outlines a shift towards taking a more holistic systems view of biology and medicine, as well as emerging capabilities to redesign life at multiple levels beyond just genetics, while emphasizing important underlying principles needed to truly understand life’s complex organization and functions.

  • The COVID-19 pandemic highlighted how little we understand about individual human responses to infection, despite having detailed molecular knowledge of viruses like SARS-CoV-2. Outcomes ranged from asymptomatic to severe illness and death in unpredictable ways.

  • Vaccines were developed quickly using protein fragments or RNA encoding viral proteins to stimulate immune defenses. However, vaccine effectiveness and side effects varied between individuals in unpredictable ways. While most vaccinated people only had mild illness if infected, some still got severely ill or died.

  • The story reminds us that while we can determine genetic/molecular details, higher biological levels have their own rules and autonomy. Changes at genetic/molecular levels can impact whole organism behaviors, and vice versa, in complex interactions across levels.

  • It highlights the limitations of reductionist perspectives that view biology as starting “at the bottom” and filtering up. A more sophisticated view of biological causation that considers interactions across levels is needed to understand life and intervention outcomes.

In summary, the passage discusses the unpredictability of individual COVID responses despite molecular virus knowledge, and limitations of reductionist perspectives in biology. It emphasizes the need to consider interactions across biological hierarchical levels to better understand life.

  • The mild case of flu described mostly cause no or minor side effects for most people. However, a tiny minority experienced unpleasant side effects like potentially life-threatening blood clots.

  • While the chances of serious side effects were very small, still lower than risks from catching the virus without vaccination, one had to hope they did not become the unfortunate few impacted.

  • This presents an interesting contradiction - modern science has greatly advanced our understanding of pathogens and vaccine development, yet we still rely heavily on trial and error and luck when it comes to individual outcomes from diseases and medicines.

  • While we can map life at the atomic level, there is still something missing in our ability to better predict and control individual biological responses, even as our knowledge and technologies improve tremendously. More understanding is needed of what we are still missing.

  • In the 19th century, scientists began to understand that cells are the fundamental unit of life. Rudolph Virchow popularized the concept that “all cells come from cells”, meaning cells multiply through cell division.

  • Advances in microscopy revealed that cells have internal structure and organization, including structures like mitochondria, membranes, and chromosomes. However, understanding the functions and dynamics of these internal structures remained challenging.

  • In the early 20th century, the term “organization” was used vaguely to refer to aspects of life that were not well understood. Scientists recognized they needed to understand general principles, not just accumulate facts.

  • Biology relies heavily on metaphor to grapple with life’s complexity. Metaphors like “vitalism”, “mechanism”, “organization”, and “information” have all been used. While useful initially, metaphors risk becoming mistaken for literal explanations if their limitations are forgotten.

  • Truly understanding life requires moving beyond analogies to man-made technologies like machines. Life cannot be reduced to its parts or turned on and off. Even machines are more complex than simplistic input-output models might imply. Understanding life demands its own unique conceptual frameworks.

  • The metaphor of cells as computers and genes as code is a poor one. It depicts life as a clumsy mixture of the mechanical and anthropomorphic.

  • Some biological entities like the bacterial flagellar motor seem mechanistic, resembling rotary motors. But few structures translate so directly to familiar mechanical notions.

  • Molecular phenomena at the cellular scale, like randomness and molecular vibrations, make machine metaphors fuzzier. Proteins and biological “assembly lines” don’t employ the same principles as human-made machines.

  • Life cannot be fully understood by fitting it into the image of present machines. Artificial intelligence and computer algorithms are beginning to be inspired by biological principles like learning, randomness, and evolution.

  • Rather than demolishing machine metaphors, we should complicate them and demand they not be used lazily or misleadingly. Biology is not vigilant about scrutinizing its metaphors.

  • The passage questions what life actually is, noting that common definitions based on criteria like self-reproduction fail to fully capture it. It argues understanding how life works cannot be fully divorced from questions about life’s purpose or meaning.

  • The passage discusses the concept of “meaning” in biology and argues that meaning is a key aspect of life that has not been fully incorporated into scientific theories. Living things attribute meaning and value to their environments in order to survive and propagate.

  • It claims life can be defined as “meaning generators” - entities capable of assigning value and finding purpose or points in the universe. While this may not encompass all forms of life, it is central to how most life operates.

  • Evolving through natural selection is key, as it is a goal-creating process that results in organisms with purposes and functions. Organization in life is goal-directed rather than just orderly like in crystals.

  • More data collection in biology is not always helpful without accompanying theories and hypotheses to interpret the data. An over-emphasis on amassing datasets risks ignoring the need for explanatory frameworks. Understanding life requires incorporating concepts like meaning that evolution bestows on living things.

  • The passage discusses how the discovery of DNA’s structure by Watson, Crick, Franklin, and Wilkins in 1953 launched the genetic age, but notes some flaws in Watson’s telling of the story in his book The Double Helix.

  • It argues that talk of discovering “the secret of life” in DNA was misguided, as life cannot be fully captured or understood at the level of any single molecule, cell, or organism.

  • Explanations of how life works have tended to focus on two scales - the visible scale of organisms, species, and ecosystems, as observed by Darwin, and the molecular genetic scale after DNA’s role was understood.

  • However, neither focus fully captures life, as an understanding of cells, immune/digestive systems, neural/endocrine functions, and the experience of being alive require looking at broader biological organization and integration across scales.

  • The passage aims to explain how life works by considering causal connections and dynamic relationships between biological components across multiple organizational levels, rather than focusing only on genes or individual parts.

  • Traditionally, we are taught that genes encode proteins, which orchestrate cellular processes to assemble cells into tissues and organisms. This view portrays genes as a genetic blueprint or program that unfolds according to its instructions.

  • However, modern biology has revealed this view to be an oversimplification. Genes are not isolated master controllers, but complexly interconnected with myriad cellular and environmental factors. Development does not proceed in a straightforward, deterministic way from genes to organisms.

  • While the traditional view remains useful for basic education, a more accurate understanding is needed given genetics’ growing role in medicine and society. Misconceptions could hinder science, policy, and public trust.

  • The real story of life is far more intricate than a linear flow from genes to traits. Current biology education may be due for an updated framework that better reflects how genes actually work within living systems.

  • The passage discusses how molecular biology and cell processes were previously seen as too complex and difficult to understand. Researchers were baffled by the interconnected workings.

  • Over the past few decades, our understanding has improved. We now recognize that processes cannot be reduced or atomized, and that each level depends on information, context and causal relationships from other levels. Genes are simply components that participate in processes, not the sole determinants.

  • However, there has been a tendency called “geneticization” to oversimplify and attribute everything to genes/DNA. Genes have taken on an almost magical or essential role in popular perceptions. Scientists are partly to blame for promoting this narrative of genetic determinism.

  • The passage traces the historical development of ideas about heredity and genetics. It discusses early proposals like Darwin’s pangenesis theory and the work of Mendel that helped clarify the concept of discrete inherited traits or “genes.” However, the full understanding of genes as encoded hereditary information on chromosomes emerged much later.

  • In summary, the passage looks at how molecular processes are much more complex than previously assumed, but also how genes have incorrectly taken on an exaggerated role in both scientific and popular thought as sole determinants of traits and identities. A more nuanced and multifaceted view is now emerging.

  • Gregor Mendel in the 1860s conducted experiments on pea plants that demonstrated traits are inherited through discrete factors (genes) in a predictable way, though he did not understand the underlying mechanisms.

  • Mendel’s work was not widely read or recognized at the time, in part because its implications for evolution were not clear. It was seen as supporting ideas of hybrid traits reverting to parental types.

  • In the early 20th century, scientists like de Vries, Fisher, and Haldane reconciled Mendelian genetics with Darwinian gradualism through mathematical models of natural selection on alleles.

  • Evidence mounted that genes are physical entities, likely molecules, supported by X-ray mutagenesis experiments in the 1930s.

  • Chromosomes were identified as potential loci of genes based on their behavior during cell division. They contain both protein and DNA.

  • Experiments in the 1940s-50s by Avery, McCarty, Hershey, and Chase provided strong evidence that DNA, not protein, is the genetic material based on its role in bacterial transformation and viral replication.

So in summary, Mendel established basic inheritance patterns but not mechanisms, which were later elucidated through modeling and molecular experiments implicating DNA as the genetic material.

  • Watson, Crick, Franklin, and Wilkins discovered the structure of DNA in 1953 - a double helix with nucleotides (A, C, G, T) paired on each strand. This supported the idea that genes reside in DNA and are encoded in the nucleotide sequence.

  • However, not all biologists immediately accepted that genes are located in DNA. Some still saw genes as indivisible units like beads on a string. But work by Benzer in the mid-1950s showed genes have internal structure at the single base pair level.

  • The gene concept emerged from ideas of inheritance and genes as molecular entities that convey traits. But there was no full reconciliation of the “evolutionary gene” that mediates inheritance versus the molecular gene that functions in cells.

  • In the 1940s, Beadle and Tatum’s experiments on mutations inbread mold supported the “one gene, one enzyme” hypothesis - that each gene controls a single chemical reaction/enzyme.

  • In the 1950s, Crick proposed genes encode the amino acid sequence of proteins. The genetic information is transferred from DNA to mRNA to protein through transcription and translation.

  • In 1956, Crick formulated the “Central Dogma” outlining the direction of information flow from DNA to RNA to proteins, with some exceptions. Experimental work in the 1960s by Matthaei, Nirenberg and others helped uncover the details of the genetic code.

  • The early pioneers of molecular biology envisioned a simple flow of information from DNA to proteins via genes and the genetic code. However, our modern understanding has become far more complex.

  • DNA is rarely seen as its canonical double helix structure. In cells, DNA is packaged into chromatin - a complex of DNA, histone proteins, and other molecules. DNA is tightly wound and compacted to fit inside the nucleus.

  • Chromatin exists in either an open, accessible form called euchromatin, or a more densely packed form called heterochromatin. The structure and organization of chromatin is carefully controlled and important for gene regulation and expression.

  • Individual genes are accompanied by promoter and enhancer sequences that regulate when and how genes are transcribed. Enhancers can be located far from the genes they influence.

  • The genome also contains many duplicated genes and transposable elements that can insert copies of themselves throughout the DNA. Duplications provide raw material for evolutionary innovation but also add complexity.

  • Overall, the process of gene expression and regulation is far more intricate than envisioned early on, involving multiple levels of organization and packaging of DNA in the cell.

  • The traditional view was that genes have direct and specific functions that map clearly to traits or phenotypes. However, research began showing genes often had multiple, seemingly unrelated functions.

  • For example, the Wnt/wg gene was first discovered to play a role in Drosophila body segment formation. But it was later found to also be involved in mouse cancer when mutated.

  • Gene knockouts often didn’t produce clear or expected results. Effects were sometimes lacking or different than predicted based on the gene’s initially understood function.

  • This challenges the idea that genes have single, defined functions tied to particular traits. Genes seem to operate in complex networks and pathways, with interactions that make precise functions difficult to determine. Their roles depend highly on context.

  • The relationships between genes, molecular pathways, and higher-level traits are far more intricate and nuanced than initially thought. Defining what a gene “does” can be problematic given this complexity.

In summary, research began undermining the view that genes have direct, one-to-one mappings to traits or functions, showing their roles are more context-dependent and interconnected than simplistic models portrayed.

  • Src is a protein involved in regulating the cell cycle that may activate itself and influence developmental pathways through interactions with other molecules.

  • Early research found that mice lacking the p53 gene, also involved in cell division regulation and linked to cancers, developed normally despite being tumor-prone later in life. This null result challenged assumptions.

  • Redundancy cannot fully explain such results, as cell signaling is not like clearly defined pathways with backups. Compensating actions further down the line are more important than direct replacements.

  • Genetic control of development is complex, as genes may influence things in unknown ways and phenotypic consequences cannot be predicted. Minor genetic effects are often retroactively defined as important questions.

  • Initial projections vastly overestimated the human gene count, which was found to be only around 20,000 protein-coding genes, challenging beliefs about genetic complexity.

  • Our understanding of genes has evolved beyond just encoding proteins. Non-coding DNA also has important roles. Genes are emergent features that cannot be defined statically or located precisely.

  • The genome resembles the integrated brain more than a linear code or blueprint. It supplies resources for cells rather than strictly controlling them. Genes impart capabilities, not predetermined outcomes.

  • Genomic data has enabled stronger correlations between genes and traits by allowing comparison of genomes that differ in just one or a few alleles. Large datasets are needed to identify even small genetic influences.

  • Genome-wide association studies (GWAS) look for statistical correlations between genetic variants like single nucleotide polymorphisms (SNPs) and traits like height, disease risk, etc. across many individuals.

  • While genes are correlated with traits statistically, they do not deterministically “make” traits. Other environmental factors are also involved, and genes alone cannot perfectly predict individual outcomes.

  • Saying genes “matter but don’t make a difference” obscures the role of environmental influences like parenting. While genes may account for statistical variance, individual outcomes are diverse and complexly determined.

  • Using genetic screening to select for traits like intelligence risks elevated expectations that cannot be guaranteed, and commodifies reproduction. There are no isolable “intelligence genes.”

  • The picture from genomics casts doubt on viewing inheritance as discrete genes. Non-coding DNA and regulatory regions seem importantly implicated in complex traits. Understanding the full picture requires considering genes in interaction with the environment.

  • The genomic era has challenged the idea that genes are the central units of biological function and inheritance. Researchers now argue we are in a “postgenomic era” where genetics is no longer focused solely on genes.

  • Studies of genetic variants associated with traits (GWAS) show that most human traits are influenced by many genes, not just a few major genes. Even strongly hereditary traits like height are polygenic, influenced by many genes with small effects.

  • It is difficult to determine the exact causal roles of individual genes from correlation data. Genes linked to traits don’t always have obvious functional relevance.

  • The “omnigenic model” suggests that almost any gene may have some effect on core genes that directly impact diseases or traits. Traits are influenced by a diffuse network of many genes interacting across the genome.

  • This makes it hard to isolate individual genes as having significant causal roles. Phenotypes emerge from dynamic interactions across the whole genome rather than direct effects of single genes.

  • The genetic basis of traits and evolution is also highly polygenic and diffuse, without reliance on specific key genes of large effect. Adaptation occurs through small frequency changes in many genes.

  • In the 20th century, genes came to be seen as the fundamental “atoms” of evolution by geneticists and evolutionary biologists. Life was viewed as all about the propagation and spread of genes through populations.

  • This “gene’s-eye view” sterilized biology by reducing organisms to mere vehicles for gene replication. It discouraged curiosity about developmental and cell biology processes.

  • The divergence between genetics/evolutionary biology and developmental biology stemmed from early 20th century enthusiasm for Mendel’s work, which emphasized discrete inherited factors (genes). Development was seen as a “black box.”

  • However, the fields of evo-devo and genomics have narrowed this divide by exploring how evolution shapes developmental systems. They also show how the developmental and evolutionary meanings of “gene” are different and sometimes irreconcilable.

  • Evolutionary and developmental biology seek different kinds of explanations and focus on different levels - populations versus individuals. Their concepts of what a gene is also differ.

  • Organisms acquire form twice - through evolution recorded in genomes, and through developmental interactions of molecules and cells, both under genetic influence in different senses.

So in summary, the passage discusses how the gene-centric view dominated 20th century biology but has been challenged by newer fields bringing developmental perspectives back into consideration. It argues for a pluralistic, context-dependent understanding of the term “gene.”

  • The concept of the “gene” has limitations in understanding how organisms develop and function. Seeing genes as rigid, unitary entities misses how they interact in complex networks.

  • Problems arise when evolution and development are seen as governed by the same kind of gene. The “evolutionary gene” and “developmental gene” play different roles.

  • Richard Dawkins’ notion of the “selfish gene” was meant metaphorically to explain natural selection, not literal gene behavior. However, the metaphor suggested genes compete against each other, which is not accurate.

  • Genes in an organism usually cooperate to facilitate development. Different alleles of the same gene may compete, while different genes cooperate.

  • Selection ultimately acts on the organism, not the gene directly. While changes in genes can influence selection, the connection is complex, not simple or direct.

  • The debate around levels of selection (gene vs. organism vs. group) stems from difficulties describing thegenotype-phenotype relationship and causal influences across interaction networks.

So in summary, the context questions rigid views of genes and selection, arguing for more nuanced, complex understandings that acknowledge the multilayered interactions shaping organisms over development and evolution.

Here is a summary of the key points about phenotype from the passage:

  • Genes are not the primary causal agents determining all organismic life and development. Other biological and environmental factors are also important.

  • While genotypic (gene) changes often correlate with phenotypic (observable trait) changes, the relationship is complex and not always straightforward.

  • Different causal stories can be told to explain genotype-phenotype correlations, and there is debate around which story is most accurate in different contexts.

  • Dawkins’ narrative of genes causing phenotypic changes that then undergo selection portrays a direct causation, but this is an oversimplification and not universally true, especially for complex organisms.

  • Genes do not have true autonomous agency or replicating ability. They depend on the organism and larger biological system to be replicated and evolve. Imputing genes with agency goes too far.

  • Phenotypic differences can arise even between identical twins who share the same genome, showing that genes alone do not determine outcomes and traits depend on gene expression and development as well.

So in summary, the passage questions genetic determinism and views genes as having correlational rather than solely causal relationships with phenotypes, with development and environment also playing important roles.

  • The passage discusses how our understanding of transcription and RNA has evolved over time. Initially, RNA was seen as simply mediating the transfer of genetic information from DNA to proteins.

  • In the 1960s-70s, researchers discovered that eukaryotic cells transcribe more RNA (heterogeneous nuclear RNA or hnRNA) than is exported as messenger RNA (mRNA). Much of the hnRNA gets broken down.

  • It was then discovered that mRNA is actually pieced together from fragments (exons) of hnRNA, with introns being snipped out. This challenged ideas of genetic economy, as introns are faithfully copied but not needed for proteins.

  • Researchers are now realizing RNA plays a much bigger role than just transferring genetic information. Discoveries like splicing suggest key cellular information processing depends on RNA.

  • The passage discusses Barbara McClintock’s pioneering work showing some DNA elements (transposons) can move within chromosomes and regulate nearby gene activity. This challenged fixed views of genes and showed RNA’s role in gene regulation.

In summary, the passage traces how our understanding of transcription and RNA evolved from a simple view to realizing RNA plays a central role in cellular information processing and gene regulation.

  • Barbara McClintock discovered “mobile controlling elements” or transposons in maize in the 1940s and 1950s. She proposed they acted as regulators of genes by controlling when and where genes are expressed.

  • This was a major advance that challenged existing ideas about the static nature of the genome. However, it was initially met with skepticism, partly due to gender bias against female scientists.

  • In the 1960s, Jacques Monod and François Jacob provided further evidence for gene regulation by studying the lac operon in E. coli bacteria. They showed how a repressor protein regulates whether genes for lactose or glucose metabolism are activated.

  • It’s now understood that gene regulation is often orchestrated by noncoding RNA molecules rather than proteins. Studies of X chromosome inactivation in females led to the discovery of long noncoding RNAs like Xist RNA that play regulatory roles.

  • McClintock’s ideas about dynamic genome regulation through mobile elements were ahead of their time, though the specific mechanisms she proposed were incorrect. The basic concept of gene regulation through various mechanisms is now firmly established.

  • Antisense RNA (Airn) regulates gene expression in a double-negative fashion by inhibiting an inhibitor gene called Igf2r.

  • It works by interfering with Igf2r transcription through transcriptional interference. The DNA encoding Airn overlaps with Igf2r’s promoter region, so transcription of Airn occupies the RNA polymerase enzymes and prevents them from transcribing Igf2r.

  • Often with long non-coding RNAs (lncRNAs) like Airn, it is the process of transcription itself that is important for gene regulation, not the finished RNA product. The transcription acts as a “distracting decoy” that interferes with other genes.

  • Another example is a ncRNA called Bendr that regulates the Bend4 gene. Transcription of Bendr turns on an enhancer within its DNA that enhances Bend4 transcription. Again, the ncRNA itself is not important - its transcription serves as a signal to activate the enhancer.

  • So in these cases, lncRNAs regulate genes in a dynamics process of transcriptional interference or activation, rather than through the information content or function of the final RNA molecule. The transcription is more important than the transcript.

  • The debate centered around how much of the human genome is “junk DNA” with no function. ENCODE claimed much more is functional than previously thought, implying purpose and intelligent design.

  • Critics like Doolittle argued most DNA may not be under strong selective pressure and functional role doesn’t imply purpose. Not all that aids survival is hereditary.

  • While ENCODE showed more transcription than realized, not all RNA is meaningful. Some could be “noise.” Function also doesn’t mean purposeful adaptation.

  • Noncoding DNA plays a larger role in complex organisms. Over 90% of bacterial DNA codes for proteins, but it’s only 2% for humans, with more regulatory RNA.

  • Penny quipped the human genome seems badly designed vs. E. coli’s elegant design - reflecting our poor understanding of complex genomes ordered by noncoding RNA regulation, not just proteins.

  • Monod said what’s true for bacteria is true for elephants, but noncoding RNA regulation, not just proteins, distinguishes complex from simple organisms. ENCODE challenged 50+ years of misunderstanding gene regulation in complex life.

Biological complexity is driven in large part by regulatory RNAs and epigenetic processes that control gene expression and cell differentiation during development. Epigenetics refers to mechanisms that regulate which genes are turned on or off without altering the underlying DNA sequence.

Two key epigenetic mechanisms are DNA methylation and histone modifications. Methyl groups can be added to DNA at CpG sites near gene promoters, typically suppressing transcription. Histone proteins around which DNA is wound can also be modified with methyl, acetyl, phosphate and other chemical groups. These histone marks influence whether genes are expressed by altering chromosome structure.

Dynamic epigenetic regulation is crucial for cellular differentiation during embryogenesis and for tissue-specific gene expression. The same genome can give rise to diverse cell types through differential epigenetic programming. Environmental factors like nutrition, stress and lifestyle can induce epigenetic changes that impact gene regulation and phenotypes. This blurring of nature and nurture helps explain why identical twins are not genetically identical. Epigenetics creates a feedback loop whereby the cellular environment influences the epigenome which in turn shapes the cell phenotype and organism development.

  • Euchromatin is loosely packed chromatin where genes are more accessible for transcription. Heterochromatin is more densely packed, inhibiting gene transcription.

  • Histone modifications can regulate genes by altering chromatin structure. Acetylation makes chromatin more open while deacetylation compacts it, inhibiting transcription.

  • Methylation marks on DNA are more stable while histone marks are more ephemeral. Epigenetic marks create an additional regulatory code beyond the genetic code.

  • Epigenetic marks are largely erased in germ cells like eggs and sperm, so they don’t directly impact inheritance. However, some epigenetic inheritance is possible, like in plants.

  • While epigenetics is important for gene regulation, it does not fundamentally challenge evolution and is of marginal relevance to it. Epigenetics provides a mechanism for rapid adaptability without needing to evolve genes themselves.

  • Epigenetics should be seen as a fundamental part of how genomes regulate themselves rather than a modification of genetics. It represents an adaptation for producing rapid responses to environmental changes.

In summary, it outlines the basics of epigenetics, how it relates to gene regulation and inheritance, and argues it is an evolved mechanism for adaptability rather than a revolution in biology.

  • The evolution of RNA regulation and editing enzymes in the brain could have enabled advanced cognition to evolve in humans and other species. RNA regulation allows for complexity at the cellular level that is not dependent on genomic changes.

  • This proposes that the increased plasticity from RNA regulation was able to influence complexity at the behavioral/organismal level in an influential way.

  • While speculative, the core idea is worth considering - that complexity in cell-level processes like RNA regulation did not just coincidentally evolve parallel to increased behavioral complexity, but may have facilitated and driven each other. RNA regulation could have been a key enabling factor for more advanced cognition and behavior to emerge over evolutionary timescales.

Here is a summary of the key points in section s (fig. 4.3):

  • Figure 4.3 shows the two most common folding motifs in proteins: the alpha helix and beta sheet. These are basic structural elements that proteins often adopt.

  • The process of protein folding, by which the polypeptide chain takes on its compact 3D structure, was long considered one of biology’s biggest puzzles. It’s not clear how the chain is able to find the correct folded conformation out of the enormous number of possible alternatives.

  • In 1969, Cyrus Levinthal pointed out this “protein folding problem”. He estimated that the number of possible folded conformations is astronomically large, far more than the number of atoms in the universe. Yet proteins are able to fold reliably and quickly find the correct native structure.

  • It is now thought that the energy landscape that governs protein folding is funnel-shaped, rapidly channeling the folding process toward the native structure. This helps explain how proteins can fold correctly without needing to test every possible conformation.

  • Specifying just the amino acid sequence appears to dictate the folded structure. The goal is to be able to predict protein structures computationally from sequence alone.

  • X-ray crystallography is a technique that uses X-rays to determine the positions of atoms within crystalline materials like salts, minerals, and proteins. The technique works by firing X-rays at a crystal and analyzing the diffraction pattern to deduce the positions of atoms in the crystal lattice.

  • Early pioneers realized this technique could be used to determine protein structures if proteins could be made to form ordered crystals. However, determining protein structures is much more complex than small molecules due to their large size and complexity.

  • Advances in computing facilitated solving protein structures using X-ray crystallography starting in the 1930s. Key early structures included insulin and hemoglobin. Over 65,000 protein structures have now been determined using this method.

  • Cryo-electron microscopy is another important technique for determining complex molecular structures, including large protein assemblies. It works by flash-freezing samples and using electron beams instead of light, allowing higher resolution images.

  • It was traditionally believed that a protein’s structure dictates its specific function, such as enzymes being perfectly shaped for catalysis. However, functions can be influenced by other molecules through allosteric regulation. Determining three-dimensional structures continues to provide insights into protein function.

  • Proteins can exhibit allostery, where the binding of one ligand affects the protein’s ability to bind or interact with another ligand. For example, enzyme A may not be active until it binds ligand B, which causes a conformational change exposing the active site to convert ligand A to product P.

  • Allostery allows proteins to function like logic gates, with ligands as inputs and products as outputs. Binding of certain ligands can switch the protein between active and inactive states.

  • G-protein coupled receptors (GPCRs) are a major class of proteins that function allosterically. Binding of a ligand on the extracellular side leads to a shape change activating the intracellular side to interact with G proteins.

  • GPCR signaling often activates protein kinases in a cascade, which phosphorylate other proteins and modulate their activity. Phosphatases remove phosphates to reverse this.

  • While proteins were viewed as rigid machines, they are actually soft and deformable. Additionally, many proteins contain intrinsically disordered regions that do not have a well-defined structure. These disordered regions allow for multiple, ligand-dependent conformations and binding partners.

  • Many proteins are intrinsically disordered, meaning they lack a single stable structure and exist as flexible ensembles of conformations. This allows them to bind multiple similar partners.

  • Intrinsic disorder allows proteins to have different types of disorder tailored to their functions. Compact disordered structures can bind DNA effectively.

  • Disordered proteins can transmit signals through allostery without precise engineering. Phosphorylation can remodel disordered proteins to change their functions.

  • Misfolding of disordered proteins like tau and prions can cause neurodegenerative diseases like Alzheimer’s and CJD. Prion proteins can transmit their misfolded state to normal prion proteins.

  • Disordered proteins act as hubs in cellular networks but their flexibility increases risk of pathogenic aggregation if misfolded. Many disease proteins are enriched in disordered regions.

  • Intrinsic disorder may enable non-genetic inheritance of traits in yeast through disordered protein transmission between dividing cells, similar to prion inheritance.

  • Researchers studied intrinsically disordered proteins (IDPs), which lack stable 3D structures, in yeast. They found IDPs can be inherited through protein-based mechanisms independent of DNA.

  • This protein-based inheritance allowed genetically identical yeast cells to develop different phenotypes quickly in response to environmental stress like lack of water. It provided a way for variation to emerge without genetic changes.

  • The researchers suggested this could be an “emergency reservoir of variation” that allows populations to explore new survival solutions under stress. However, it’s unclear if multicellular organisms could use this strategy given cells have specialized roles.

  • In other words, the findings raise the possibility that IDPs represent a non-genetic, protein-based mechanism for acquiring new traits rapidly during environmental stress. This could provide populations flexibility to respond to survival challenges without relying on slower genetic changes. But more research is needed to understand if this strategy could work for complex organisms.

  • Proteins are often made up of modular domains that can be reshuffled to create new multidomain proteins with novel functions. Many domains originated in bacteria as single-domain proteins and were combined in eukaryotes.

  • Alternative splicing and having genes encoded in exons facilitates the rearrangement of domains. This is a more efficient way for evolution to create new proteins than building them from scratch.

  • About 80% of metazoan proteins are multidomain, formed by combining existing single-domain modules. Common domain architectures include membrane proteins with a transmembrane domain linked to a soluble domain.

  • Random associations and weak interactions between proteins allow for evolutionary innovation as new functional connections can form. Hubs like the “evolvosome” may enable useful new protein partnerships to emerge through chance encounters.

  • Evolution has predominantly reshuffled existing protein domains rather than designing new proteins de novo. This modular approach using existing stable folds has been important for generating the diversity of proteins needed for multicellular life.

  • TBP (TATA-box binding protein) is one of the first transcription factors to bind to gene promoters during transcription initiation in eukaryotes. It helps recruit RNA polymerase II to begin RNA synthesis.

  • The transcriptional machinery involves a diverse set of proteins working together, not always the same proteins each time. Regulation may be looser and more dynamic than previously thought.

  • Scaffold proteins help mediate connections between signaling pathways in cells. They do this by bringing interacting proteins together physically in the same space.

  • Traditionally scaffold proteins were seen as having fixed binding sites that precisely positioned interacting partners. But many scaffold proteins are intrinsically disordered and dynamic, able to improvise new connections.

  • Scaffold proteins can act as molecular switches by recruiting/releasing binding partners. They help integrate and tune signal strength but are not precise circuit boards holding proteins in fixed positions.

  • Our understanding of protein structure and function has shifted from seeing proteins as having static, defined structures that precisely encode their roles. Intrinsic disorder is widespread and important for plasticity and promiscuous interactions.

  • Signaling and regulation in cells is more dynamic, context-dependent and open-ended than the rigid gene-protein blueprint model suggested. Protein functions emerge from complex interplay within the cellular environment.

  • Systems biology aims to map out cellular networks and interactions between genes, proteins, RNA, etc. in order to model and predict their behavior through computer simulations.

  • For simple organisms like bacteria, gene regulatory networks can be accurately mapped and engineered through synthetic biology. But for complex multicellular organisms, the networks are exceedingly complicated.

  • Some challenges include gene regulatory elements being scattered throughout the genome rather than localized, and interactomes seeming impossibly complex with many molecules needing to interact precisely at once.

  • The original view of selective, defined molecular conversations may be an oversimplification. Cellular processes may involve more diffuse, context-dependent interactions than neatly mapped circuits or logic gates. Modeling their behavior through networks alone poses difficulties without incorporating spatial and environmental factors.

  • While systems-level understanding provides insights, a more comprehensive picture is still needed to fully understand development, physiology, and information flow at the molecular level in complex living systems.

  • Early models of gene regulation proposed highly complex protein complexes formed by the precise assembly of 12+ molecules. This was seen as improbable given the crowed, chaotic environment in the cell.

  • Interactions between biomolecules are not always precisely selective. Some proteins bind promiscuously to multiple partners with varying specificity. This makes simple network models inadequate.

  • Gene expression is influenced by enhancer sequences that can be very far from the gene. This implies physical interaction through folding/bending of chromatin.

  • Chromatin organization into loops brought by cohesin and CTCF proteins helps bring distant regions like enhancers and genes into proximity for regulation.

  • Loop formation is still imperfectly understood given the chaotic, heterogeneous environment in the nucleus. Precise contacts seem improbable but cells have mechanisms like chromatin looping to impose some control.

  • Gene regulation involves many participants beyond enhancers and genes, including promoter regions, transcription factors, and cofactors operating in groups in complex coordinated processes not fully understood.

  • Gene expression is regulated by complexes of many molecules interacting together, not just individual switches turning genes on and off.

  • The genome is organized into compartments, topologically associating domains (TADs), and chromatin hubs where regulatory elements cluster together. This 3D organization is important for gene expression.

  • Insulator elements help partition the genome into TADs. Epigenetic marks help recruit chromatin into the same TADs/hubs.

  • TADs/hubs act like committees where regulatory proteins and DNA elements gather together transiently to collectively regulate gene expression.

  • Rather than static structures, TADs/hubs are highly dynamic fluid-like condensates formed through liquid-liquid phase separation. Components interact briefly but repeatedly within these localized hubs.

  • Pioneer transcription factors like Zelda help recruit other proteins to form transient, swarming hubs near genes to collectively trigger expression changes, even though individual binding events are brief.

  • This dynamic, collective process via transient condensates may be how proteins at low concentrations can achieve high local concentrations to regulate genes. But evidence for droplets in live cells is lacking and how they disperse is still unclear.

  • Cells use “phase separation” or liquid-liquid phase separation to spontaneously form membraneless compartments called condensates or condensation droplets. This allows efficient organization of cellular processes without requiring genetic specification or construction of elaborate structures.

  • Transcription factories and other nuclear bodies like P granules and the nucleolus have been shown to exhibit properties of liquid condensates that organize processes like gene regulation and RNA/protein production.

  • Changes in gene expression can trigger formation or dissolution of condensates, while condensates can in turn influence gene expression levels. So there is bidirectional information flow and integration between genetic and physical processes in the cell.

  • Intrinsically disordered proteins that are “sticky” seem well-suited for promoting condensate formation but also aggregation, so cells must balance these functions. Mutations may disrupt this balance and lead to pathogenic protein clumping.

  • Reliance on phase separation and ad hoc condensates, rather than entirely precise genetic control, allows robustness and flexibility needed to make decisions amid environmental variations and noise while integrating diverse molecular inputs.

So in summary, phase separation and liquid condensates provide an elegant physical mechanism for cells to efficiently organize processes beyond strict genetic control, through dynamic and integrated physical-genetic feedback loops.

  • BMP (bone morphogenetic protein) signaling plays an important role in tissue development and patterning through molecular interactions between BMP ligands and receptor proteins on cells.

  • The system is combinatorial, as different BMP ligands can bind to different combinations of receptor subunits, with varying strength of output signals. This allows more signaling options than a lock-and-key style system.

  • Michael Elowitz’s team characterized all the possible BMP-receptor combinations and their output signals, finding rules but also context-dependence based on cell type.

  • Some BMPs can substitute for each other in certain contexts but not others. This explains why BMP effects vary by tissue.

  • The combinatorial system provides flexibility to convey distinct messages to different cell types, allowing more complex embryonic patterning with a small set of signaling molecules.

  • While fuzzy, the system may sharpen cell fate decisions by interacting with other signaling pathways, similar to how context clarifies sentence meaning. The diversity of outputs is an advantage over a binary on/off signaling logic.

  • Molecular signaling pathways like Wnt and BMP often interact in complex ways during development, sometimes enhancing each other and sometimes antagonizing each other. This combinatorial signaling may allow for robust information processing.

  • Viruses can exploit this promiscuity, as adenoviruses produce proteins that disrupt host cell defense mechanisms by binding to various regulatory proteins and interfering with the cell cycle. This can have side effects like turning cells cancerous.

  • Signaling pathways display promiscuous and combinatorial signaling where different protein combinations can trigger various cell states. This fuzzy logic approach allows cells to be robust against noise and variation. It may be a fundamental design principle for complex multicellular organisms.

  • Promiscuous signaling promotes evolvability by allowing new functions to arise without disrupting existing ones. Eukaryotic transcription factors bind DNA sites loosely, possibly to enable this evolvability.

  • The cellular behavior emerges from interacting molecular components rather than being determined by individual molecules. Matching causal effects to the system scale, through mechanisms like combinatorial signaling, allows robust emergent behavior in complex biological systems.

  • Researchers investigated how and where causal emergence arises in networks of protein interactions (interactomes) for over 1,500 species.

  • They found significantly more causal emergence (informative macroscales where a group of protein interactions can be represented by a single higher-level node) in eukaryotes than prokaryotes.

  • Multicellular organisms tend to assign causal roles to higher levels of organization in their networks compared to single-celled organisms.

  • This allows multicellular organisms to be more robust to noise and variability at the microscale, as higher-level structures/nodes are the main determinants of phenotypes.

  • It’s unclear if this shift to higher-level causation enabled multicellularity or vice versa. Studying a single-celled ancestor of multicellular organisms suggests causal emergence at a higher level may have paved the way for multicellularity.

  • In summary, evolution seems to produce “causal spreading” where causation is increasingly conferred on higher organization levels in more complex organisms.

  • The single-celled organism Capsaspora has more complex gene regulatory networks, governed by transcription factors, than any other known single-celled organism. These networks were already in place in early multicellular organisms.

  • Capsaspora can form temporary multicellular structures, suggesting gene networks were primed for multicellularity before it fully evolved.

  • Regulation also occurs through long noncoding RNAs and chromatin packaging, but Capsaspora lacks remote enhancers, suggesting these enabled permanent multicellularity.

  • The shift to multicellularity involved new ways of regulating existing genetic material, rather than entirely new genes. This involved “tinkering” with existing gene families.

  • Changes were traditionally thought to be driven by natural selection, but some profound changes like multicellularity may have arisen through random genetic drift in small populations, not strong selection advantages.

  • Multicellularity has only evolved twice, suggesting it’s not clearly advantageous or selection may not be sufficient to drive the transition from single-celled life.

  • Gene regulation mechanisms have shifted causation to higher organizational levels over evolutionary history, with three distinct eras of regulatory change in vertebrates.

  • The regulatory changes seen in evolution seem to be associated with mechanisms that modify protein structure after translation, especially for proteins involved in signal transduction within cells.

  • Evolution discovered ways to innovate and generate new organisms by first changing how developmental genes are regulated, then how cells communicate, and then how information is shared within cells. These changes occurred at higher levels of organization rather than the genetic level, leaving traces in genomes.

  • Major evolutionary changes are more a result of reorganizing gene regulatory networks rather than modifying the protein links that form them.

  • If these views are correct, it implies that the locus of causation in life has progressively shifted to higher levels over the course of evolution through a process called “causal spreading.” Evolution discovered ways to modify organisms by changing regulatory networks rather than genomes directly.

  • To understand key evolutionary transitions like the Cambrian explosion or divergence of mammals, we need to look at changes in cellular and regulatory networks, not just genomes, as genomes now only echo changes that occurred at higher levels. Causation has spread beyond the genetic level.

  • Cells within the body are often shown as empty cavities in illustrations, but they are actually densely packed with molecules. It is astonishing that any biochemical reactions can occur given how crowded the interior of a cell is.

  • Cells take on specialized roles and structures as development occurs, with different cell types like heart, nerve, and skin cells looking very different from each other.

  • Cell fate and differentiation is not predetermined or encoded in the genome. Rather, cells make contextual and contingent decisions about their fate based on signals from neighboring cells. They effectively vote on their fate after checking in with surrounding cells.

  • New techniques allow analyzing gene transcription in single cells during embryo development. This has confirmed cellular specialization over time but also shown the process is more variable and reversible than previously thought. The exact mechanisms determining cell fate are still not fully understood.

  • Conrad Waddington proposed visualizing cell differentiation as a ball rolling down a branching landscape of valleys. This became a iconic metaphor known as the epigenetic landscape.

  • The valleys represent alternative cell fates that become progressively restricted as development proceeds. Cells are guided but not determined by this landscape.

  • The landscape emerges from cell-cell interactions during development, rather than being pre-existing. It simplifies the vast complexity of molecular interactions in cells.

  • How does such a high-dimensional system of molecular interactions give rise to just a few stable cell states, represented by distinct valleys? This dimensional reduction is not guaranteed and not yet fully understood.

  • Understanding cell fate decisions requires going beyond stories of individual molecular interactions, to more abstract explanations of how networks shape the epigenetic landscape and cell phenotypes. Mapping real landscapes using single-cell data helps explain this process.

In summary, the epigenetic landscape metaphor conceptualizes cell differentiation as cells following alternative developmental paths, but it also raises questions about how such a complex system can generate stable yet flexible outcomes during development.

  • Taking a demographic census of a nation involves accounting for all individuals and gathering information about attributes like age, gender, location, etc.

  • In biology, a similar accounting can be done at the cellular level by analyzing the transcriptome (RNA molecules), proteome (proteins), and other biomolecules in single cells.

  • Recent advances in single-cell RNA sequencing (scRNAseq) allow researchers to determine the transcription profiles of thousands of cells from a developing organism and map out cell fate trajectories.

  • Analysis of scRNAseq data shows cell fates acquiring gradually rather than abruptly, with cells following multiple routes to destinations and some switching fates. This undermines traditional discrete models of development.

  • Mapping out thousands of cells reveals gene expression landscapes with valleys corresponding to different cell types. Cells within a fate valley can still vary somewhat in their profiles.

  • Ongoing initiatives are applying these techniques to map hundreds of cell types in human tissues and explore developmental differences at single-cell resolution.

  • Researchers are using single-cell RNA sequencing (scRNAseq) to map out the “cell-fate landscape” during embryonic development. This reveals the distinct cell states (types) and trajectories between them.

  • The landscape seems robust even if genetics change, suggesting it emerges from molecular interactions more than genetics alone.

  • Distinctions in the landscape appear before morphological changes, raising questions about causality between cell states and embryo shape. The answer is likely bidirectional influence.

  • A 2021 study mapped the evolving landscape in mouse embryogenesis, showing a complex network of connections between cell types rather than bifurcating valleys.

  • Development involves subtle changes collectively across many genes, not discrete steps.

  • The landscape and cell state changes can be understood using concepts from dynamical systems theory, with stable cell states as “attractors” in the landscape that development flows toward.

  • While genetics provide raw materials, the interacting molecular networks define the available cell states and constraints on embryonic development.

  • A cell’s fate decision can be described using dynamical systems theory as rearrangement of attractor landscapes. Signals reshape the landscape to tip cells into new fates.

  • Researchers found that signaling during cell fate changes causes the attractor landscape to bifurcate, giving cells a choice between two new states. This is analogous to Waddington’s ball reaching a fork and having to enter one of two valleys.

  • Cell fate is determined by a cell’s location in 3D physical space, gene expression/transcription space, and developmental “decision space” of valleys and bifurcations.

  • Cell fates are somewhat stochastic and variable even with identical signals, due to noise in gene transcription and integration of many influences rather than a single deterministic signal.

  • This noise and variability may be a feature that allows deviations in form/function, avoiding getting stuck in undesirable states, and exploration of possibilities during development. Noise can be a biological resource rather than just a nuisance.

  • Noise and stochasticity are important features of biological systems at the molecular and cellular levels. Random mutations driven by errors in DNA replication enable Darwinian evolution.

  • Cell fate determination shows how noise can be beneficial rather than detrimental. Studies of hematopoietic stem cell differentiation found random transcriptional bursts of antagonistic fate-determining genes like Gata1 and PU.1, helping cells reliably reach different fates rather than getting stuck.

  • Similar noise-driven mechanisms determine alternate cellular states in bacteria like Bacillus subtilis, where random fluctuations in antagonistic proteins SinR and SinI create two distinct behavioral states.

  • Until recently, cell fates were thought to be fixed irreversibly after differentiation. But experiments in the 1960s showed differentiated cell genes could be reactivated.

  • In 2006, Yamanaka and Takahashi showed mature mammalian cells can be reprogrammed into pluripotent stem cells through introduction of just four transcription factors. This demonstrated cell fates are plastic and reversible through genetic manipulation.

  • Subsequent studies found direct conversion between cell types is also possible, bypassing the stem cell state. Reprogramming reveals cell fate determination is more dynamic than previously believed.

  • Cell fate and differentiation can be understood through the framework of dynamical systems and attractor landscapes. Reprogramming cells restores oscillatory gene expression patterns that keep cells in a pluripotent state.

  • The cell fate maps we have now may not be exhaustive. It’s possible to “resurrect ancient cell fates” or even generate new types of tissues by manipulating developmental signals. Rat stem cells incorporated into mouse embryos were able to form parts of the mouse gall bladder even though rats don’t normally have gall bladders.

  • Cells can be viewed as cognitive agents that make decisions about their fate based on integrating environmental information, similar to how neural networks learn. Collections of cells attain development through an evolutionary learning process encoded in gene regulatory networks.

  • Even single cells exhibit primitive forms of cognition, behaviors like habituation in ciliates. Cognition allows for adaptive, goal-directed responses and is a hallmark of living things. Life involves an “aboutness” or capacity for dealing with the unforeseen.

  • Higher levels of biological hierarchy like tissues are built from the cognitive capacities of individual cells. Understanding life may be better served by focusing on cognition rather than just metabolism and replication.

In summary, the passage discusses how cells make fate decisions through a cognitive, dynamically integrated process, suggesting cell potential and tissue organization is more complex than currently understood. It frames life in terms of cognition from the cellular level up.

  • Planarians have an extraordinary ability to regenerate after being cut into many pieces. Each small fragment can regrow into a fully formed planarian.

  • They are able to regenerate complex structures like their brain, nervous system, eyes, mouth, etc. in the right proportions without missing any parts.

  • Other organisms like axolotls and hydras also have regeneration abilities, but planarians’ skills are unmatched in their complexity.

  • Individual cells seem to “remember” the entire body plan and know what structures need to be regenerated based on what is missing. It’s unclear how they do this.

  • Cells communicate with each other in various ways - chemically through signaling molecules, mechanically by touching and pulling on each other, and electrically by exchanges of ions.

  • This allows cells to integrate information and determine patterns of growth and tissue differentiation in a coordinated, collective manner during development and regeneration.

  • Electrical coupling in particular may allow cells to “compute” and integrate signals over long ranges to regenerate complex structures precisely as needed.

So in summary, cells appear to have an extensive knowledge of the body plan collectively through intricate communication networks, even at the individual cell level, allowing precise regeneration of missing structures. But the exact mechanisms are still unclear.

  • Researchers found that if they manipulate the electrical signals in planaria flatworms, they can induce the worms to regrow heads that resemble different species, rather than just regrowing their own species’ head type. This suggests body shape is not entirely hardwired by genetics.

  • The developmental process seems to involve “attractor states” - preferred configurations that tissues settle into. Manipulating electrical signals can potentially push tissues into different attractor states, leading to altered shapes.

  • Experiments on frogs also support the idea of attractor states. Researchers disrupted facial development electrically but normal faces still emerged, suggesting a “target design” guides formation.

  • These electrical influences may provide a kind of non-neural information processing that guides development. Membrane voltage can override genetic signals in determining cell fate.

  • Overall, cells collectively navigate “morphospace” towards stable configurations, not through a strictly programmed process. Their decisions emerge from complex gene-protein-electrical interactions.

  • In mammals, symmetry breaking in early embryos occurs through interactions of surfaces and edges. The formation of structures like the primitive streak establishes the first axis that guides further shaping of the body plan.

  • The formation of the primitive streak during gastrulation marks the transition to a more developed embryo with polarity (head/tail). This process is still not fully understood in humans but occurs similarly in other species.

  • The primitive streak establishes the three germ layers (ectoderm, mesoderm, endoderm) through cell migrations. Precise signaling between genes and cell behaviors guides cell differentiation.

  • Next, the notochord forms along the bilateral axis to provide structure. It secretes signals that induce neural tube formation from the ectoderm.

  • Neural crest cells also form and will develop into tissues like the nervous system. Failure of the neural tube to properly close can cause serious birth defects like spina bifida.

  • Factors like folic acid levels during pregnancy influence neural tube development, but there is also a degree of chance in the complex mechanical process of folding and rearrangement. Rarely, twins may become fused during this stage.

  • Fetus-in-fetu occurs when a twin becomes enveloped within the body of the other twin during early embryonic development. Occasionally, the engulfed twin can continue developing into a fetus-like structure inside the other twin.

  • In 1982, British neurosurgeons removed a 14cm fetus from the brain ventricles of a 6-week-old infant, who had been experiencing abnormal head enlargement. The infant recovered after the removal.

  • Fetus-in-fetu shows that embryonic development is the result of an interaction between genes and the environment, not just genetics alone. Chance also plays a role. A similar condition can arise when a twin is engulfed in the gut of the other twin.

  • Early embryonic development involves tissue folding and shaping through a combination of gene activation/suppression, cellular communication, and mechanical forces as tissues grow and change shape. There is no single controlling influence - the processes interact bi-directionally.

  • Mechanical forces on cell membranes can trigger gene expression changes inside the cell, altering its development path. Cell shape changes then affect tissue morphology and forces. Actin/myosin cytoskeleton dynamics within cells play a key role in driving tissue reshaping and folding during development.

  • The Hippo signaling pathway converts mechanical signals at the cell surface into genetic changes in the nucleus. It controls organ size by regulating cell proliferation and apoptosis based on contact with neighboring cells.

  • Tissue growth and shape changes during development can be triggered by passive buckling and folding of cell sheets as they proliferate within physical constraints. Morphogens like Sonic hedgehog can induce differentiation and fate changes that sculpt developing structures.

  • Fluid flow also affects cell behavior - blood flow induces heart chamber differentiation in zebrafish, and lung development is shaped by air pressure.

  • Regenerating organs display an ability to “know” what shape and structure is missing and regrow it accurately, indicating top-down information feedback to governing cells. However, the exact mechanisms controlling morphogenesis and regeneration are still not fully understood.

  • Developmental outcomes are attractor states that systems converge on through diverse routes, maintaining evolutionary plasticity. Life produces genetically permissive systems with a range of phenotypic options rather than single prescribed outcomes. Canalized developmental rules and variability allow robust yet evolvable forms to emerge.

  • Regulatory networks and interconnected gene pathways mean that the genotype cannot predict the exact phenotype - there are many possible outcomes beyond what is specified by the genes alone.

  • Allowing developmental plasticity and loose topological guidance, rather than a strict blueprint, makes organisms more robust to errors and able to correct mistakes. Complex entities like humans require generative rules rather than prescriptive algorithms.

  • Some canalization of form is necessary, but it cannot be absolute. Generative rules may lead to plural outcomes, some viable and some not. Developmental “abnormalities” are the norm, what matters is degree.

  • Conjoined twins, developmental variations, and brain diversity are just possible outcomes of human development under genetic influences, not aberrations from a normative plan. Regarding them as defects hinders understanding of how life’s complexity naturally unfolds.

  • A strict blueprint view fails morally by compelling us to see reality as deviating from a normative standard, rather than development being an unfolding process with plural potential outcomes.

In summary, it argues that regulatory networks, developmental plasticity, and generative rules allow for life’s complexity but mean phenotypes are not strictly prescribed by genotypes alone. Regarding developmental variations as defects restricts understanding of life’s natural processes.

  • The passage discusses how formation of digits (fingers and toes) is guided by concentration gradients of signaling proteins called morphogens during embryonic development.

  • Early researchers proposed that morphogen gradients provide positional information to cells, letting them know where they are located and what type of structure to form.

  • Experiments in the 1960s identified the “zone of polarizing activity” (ZPA) in chicken limb buds, which secretes Sonic hedgehog (Shh) morphogen to form a gradient.

  • The Shh gradient helps pattern the limb bud by establishing an anterior-posterior axis. Transplanting ZPA cells altered digit formation, showing their organizing role.

  • Lewis Wolpert proposed in the late 1960s that passing certain concentration thresholds of the morphogen can activate different genes. This creates distinct segments like the bands of a French flag, resulting in digit segmentation from a smooth gradient.

  • In summary, morphogen gradients allow embryonic cells to gather positional information and correctly develop structures like fingers through a self-organizing process guided by gene expression thresholds along the gradient.

The passage discusses Alan Turing’s influential 1952 paper on morphogen gradients in embryonic development. Turing showed that reactions and diffusion of chemical morphogens in a spherical embryo could spontaneously break its symmetry and generate complex patterns, like those seen in organisms.

Specifically, Turing proposed that interactions between two or more diffusing morphogens could create feedback loops that transform a simple gradient into striking patterns. For example, one morphogen enhancing or suppressing another’s influence on cell fates. This more sophisticated mechanism, involving interacting morphogen gradients, helps explain how embryonic tissues acquire their shapes and structures.

Turing’s work was visionary in recognizing that pattern formation in embryos does not simply depend on thresholds in morphogen concentrations, as initially thought. Interactions between diffusing signaling molecules can collectively generate the complex organizational blueprints needed to develop segmented and asymmetric organisms from initially symmetrical embryos. This insight transformed understanding of morphogenesis and developmental biology.

  • Conrad Waddington argued that development requires more than just genes controlling protein synthesis - it needs “physical forces” to mold and shape the material.

  • Alan Turing proposed a mechanism of symmetry breaking involving two types of chemicals (morphogens) - an activator that speeds its own production, and an inhibitor that disrupts the activator.

  • With the right reaction and diffusion rates, this system could spontaneously generate patches where the morphogen concentrations differ, breaking symmetry. One morphogen could then activate genes in certain cells.

  • Turing showed this could produce regular patterns like stationary or traveling waves. He suggested it could explain animal spots/stripes, but the theory lacked biological details.

  • Later work clarified the activator-inhibitor concept and showed Turing patterns could reproduce complex markings. But few repetitive structures were known to fit the theory.

  • Recent findings indicate regular arrangements like hair follicles, feathers and scales involve activator-inhibitor networks, providing better evidence for Turing’s proposed role in morphogenesis. While complex, these repetitive structures seem well-explained by his proposed symmetry-breaking mechanism.

  • The development of feather barbs and dog palate rugae (ridges) are thought to involve reaction-diffusion patterning with proteins like FGF, SHH, BMP and Wnt. These same proteins are versatile and can be reused in different configurations for different developmental processes.

  • SHH was identified as a key morphogen in limb development. However, digit formation cannot be fully explained by a simple SHH gradient model. It appears digits arise as a Turing pattern.

  • A model involving BMP, Wnt and Sox9 interacting in a reaction-diffusion network can generate the stripe-like patterns seen in early digit development. BMP affects digit number while Wnt controls spacing. Manipulating BMP and Wnt levels impacts digit number and thickness as predicted.

  • The widening stripe pattern from root to tip is controlled by a HoxD13 gradient. This modulation allows different numbers of digits to fit depending on bud size. Five digits is common as that matches the intrinsic stripe size to spatial constraints at the developmental stage.

  • Individual digits are freed when webbing tissue between them undergoes programmed cell death. Soft tissues also adjust to skeletal changes through mechanical feedback and context-dependent rules rather than a rigid blueprint.

The passage discusses how left-right asymmetry in the human body develops during embryogenesis through a Turing-type pattern formation process.

Early in development, even at the two-cell stage, embryos distinguish left from right sides. Around the gastrulation stage, genes like Nodal and Shh are asymmetrically expressed. Later, the gene Lefty is found only on the left side and helps determine left-right patterning.

Cilia on the embryonic endoderm layer create fluid flows when they beat. Due to cilia orientation, this flow breaks left-right symmetry and moves from right to left at the front and left to right at the back.

The Nodal and Lefty proteins then amplify this weak initial fluid flow signal into a full left-right pattern through an activator-inhibitor feedback loop. Nodal activates itself while Lefty inhibits Nodal. Lefty also diffuses faster, as required for Turing patterning. This divides the embryo into left and right sides with different Nodal and Lefty concentrations, distinguishing the two sides. This initial asymmetric gene expression then guides the later positioning of internal organs to the left or right sides of the body.

  • Turing pattern formation mechanisms operate at many scales in nature beyond just animal development, like how ants deposit dead bodies or how grass grows patchily in dry areas. The same activation-inhibition processes shape ripples in sand and mineral structures.

  • Body patterning in animals relies not just on Turing mechanisms but also things like concentration gradients delivered by genes like Hox genes. Hox genes control segmentation of the body plan during embryogenesis.

  • Hox genes interact with signaling pathways to influence cell division and morphology. This segmented body plan is repeated in structures like limbs, fingers, etc. through similar positional information gradients.

  • Morphogen gradients produce robust patterning even with genetic/molecular changes, allowing organism evolution without disrupting form. Experiments show genetic factors constrain an underlying developmental plasticity.

  • The wide array of possible phenotypes hidden by factors like Hsp90 suggests genes select from possibilities determined more by physicochemical mechanisms like tissue folding or reaction-diffusion, rather than producing forms de novo. This could explain some convergent evolution through availability of forms rather than optimal adaptations alone.

  • The Second Law of Thermodynamics states that the entropy (disorder) of the universe increases over time as energy dissipates and spreads out. This implies that ordered, non-equilibrium states will naturally break down into more disordered equilibrium states.

  • Living organisms seem to defy this by actively maintaining highly ordered cell structures and physiological functions. They marshal energy to create and preserve biological order instead of degrading into randomness.

  • However, life only appears to contradict the Second Law because organisms constantly consume energy from their surroundings and dissipate heat, thereby increasing the net entropy of themselves plus their environment. So the Second Law is upheld overall.

  • The key question is why life bothers with this elaborate act of maintaining non-equilibrium order through energy consumption, when equilibrium and decay naturally take over after death. What is the purpose or goal of life’s entropy-defying tendencies? Understanding agency, purpose and meaning is a major challenge for biology.

So in summary, the passage discusses how life seems teleological in maintaining order through energy usage, while still complying with thermodynamics, and raises the question of what goals or purposes drive these entropy-defying tendencies of living systems.

  • The passage discusses how order can arise from chaotic and nonequilibrium systems through natural processes like the formation of hexagonal basalt columns, hurricanes, tornadoes, and convective cells on the sun’s surface.

  • Living organisms are nonequilibrium systems that constantly take in energy/matter from the environment to drive metabolic processes and avoid equilibrium/maximum entropy, which would lead to death.

  • Erwin Schrödinger recognized in his 1944 book What is Life? that living things avoid rapid decay into inert equilibrium by metabolizing and drawing “negative entropy” from the environment.

  • At the time, biology focused on chemical processes like metabolism but did not explain how these interconnected with genetics and inheritance. Schrödinger tried to provide a bigger picture theory.

  • He proposed life must follow a “new type of physical law” generating “order from order” rather than the disorder expected by classical thermodynamics. But the mechanism was unknown.

  • A key question is how molecular-scale changes like mutations can produce macroscopic phenotypic changes, which now seems clear through genetics and evolution but was puzzling at the time.

So in summary, the passage discusses how nonequilibrium order can arise naturally and how Schrödinger helped shift focus to understanding life as a thermodynamic phenomenon that resists equilibrium through negative entropy intake, though key questions remained unresolved.

  • Schrödinger was puzzled by how order arises at the organism scale from randomness at the molecular scale. He noted tiny genetic mutations could have large effects, contradicting expectations.

  • Schrödinger proposed genes impose order through an “aperiodic crystal” - a precise yet non-repeating structure encoding a “code-script” that directs development.

  • DNA was discovered to have this structure - a regular double helix but irregular base pair sequences. This supported Schrödinger’s idea of an “aperiodic crystal” encoding genetic information.

  • However, biology does not rely on genes rigidly imposing order. Living things cope with noise through emergence - higher-level causation arising from molecular interactions. Genetic information alone is not enough to direct a living organism.

  • Schrödinger started to glimpse how life harnesses matter towards a goal, but was missing the concepts of information and meaning. His vision reduced life to a genetic program, neglecting the richness of biology. While DNA stores information, life is more complex than a deterministic genetic code.

  • The passage discusses the concept of continuity between human attributes like relationships, art, and religious belief, and similar attributes seen in other animals like chimpanzees, dogs, and simpler organisms like bacteria. While we can’t know exactly what other animals feel, there are reasons to believe they experience things beyond just automatic reactions.

  • It talks about how organisms ascribe meaning and purpose to their environments and goals. This ability to experience meaning is key to what makes living things different from inanimate systems. We need a theory of biological information that incorporates meaning.

  • It discusses how Maxwell’s demon thought experiment from the 1800s, involving a hypothetical entity that could separate hot and cold molecules, helped establish a connection between entropy, information, and agency. Maxwell proposed it to argue against rigid determinism implied by the second law of thermodynamics.

  • Others like Thomson took Maxwell’s demon more literally as a possibility that could actually exist at the molecular scale. Some like Tait believed these demons might be real and help show compatibility between science and religion. The passage examines the historical context and motivations around Maxwell’s demon proposition.

  • Maxwell’s demon was originally proposed as a way to seemingly violate the second law of thermodynamics by separating hot and cold molecules without expending work. This appeared to allow for the creation of order from disorder.

  • Objections were raised that the demon would need to measure molecules and expend energy to do so, generating enough entropy to compensate. But later it was argued measurement itself does not intrinsically generate entropy.

  • The key insight was that while measurement is costless, erasing information from the demon’s memory is not - it must dissipate energy equal to the Landauer limit. Since the demon has finite memory, information will eventually need to be erased, preventing perpetual violation of the second law.

  • Maxwell’s demon exhibits agency by collecting meaningful information about molecule energies, storing it in memory, and acting on that information to manipulate its environment goal-orientedly. This connects information theory and thermodynamics - by using information, a system can build order and do work as long as it has memory, only generating entropy when memory is erased.

  • Living systems seem to employ similar strategies as Maxwell’s demons through mechanisms like ion pumps and motor proteins, but actually consume energy like real pumps rather than operating without cost.

  • Living organisms correlate with and attune to their environment in order to harvest energy and avoid reaching equilibrium, allowing them to survive. They do this by acquiring, storing, and using meaningful information from the environment.

  • Natural selection has driven biological systems to be extremely efficient in their computation and information processing, aiming to minimize thermodynamic costs. Organisms tend not to overthink survival but reduce unnecessary computation.

  • To efficiently use available energy, biological systems function as “prediction machines” - they construct representations of the environment to anticipate the future and guide behavior. Even single cells and molecules implicitly represent surroundings.

  • For a system to act as a genuine agent (causal force of change), it must be out of equilibrium with its environment, have a boundary to maintain autonomy, persist over time, and exhibit endogenous (self-generated) activity not fully determined by external factors. Agency may emerge at higher levels of organization rather than just atomistic interactions.

  • Attributing meaningful agency is important for understanding life, though metaphors should not be overextended. Formalizing agency criteria can help locate it appropriately in biological systems without anthropomorphizing or mechanistic reductionism.

  • Traditional views in biology saw purpose or teleology as central, from Aristotle thinking objects have intrinsic purposes to falling, to Paley arguing living things show design by a Creator.

  • Darwin’s theory of evolution by natural selection demolished this by explaining how natural forces alone, without planning or purpose, could produce organisms that appear perfectly designed for their functions. Evolution is a “blind watchmaker”.

  • Biology has since tried to remove purpose or goals from explanations, seeing evolution as a random, contingent process without intrinsic direction.

  • However, the idea of intelligent design has attempted to re-introduce purpose by arguing some biological features are too complex to have evolved randomly and must have been guided. But these arguments have little scientific support.

  • More recently, recognizing organisms exhibit agency and seek goals raises the challenge of how to conceptualize purpose in biology. An agent-based, teleological view may need to be re-incorporated, focusing on organisms’ endogenous reasons and embedded purposes rather than external design.

So in summary, it traces the history from early intrinsic purposes to Darwin removing purpose, to modern debates trying to re-introduce ideas of goal or purpose based on recognizing life as agentive rather than mechanistic.

  • Natural selection seems able to create complex features in organisms that initially elicit incredulity like “how could natural selection have made that?“. But current evidence shows that atomic-level physical laws are sufficient to explain what we find in nature.

  • Biology aims to remove teleology (purpose/goals) from explanations to avoid pre-Darwinian notions. It speaks of organisms behaving “as if” they have purposes but maintains this is just a manner of speaking. Daniel Dennett coined the “intentional stance” to interpret behavior as rational choice based on beliefs and desires.

  • Ernst Mayr accepted that purposive goal-directed behavior is widespread in animals, and proposed the term “teleonomy” to describe evolved programs that confer goal-directedness. He distinguished closed programs fully specified by DNA from open programs incorporating lifelong learning.

  • However, no genotype contains complete instructions, and responses depend on past history. Genomes provide recipes for possible behaviors rather than programs. Goal-directedness is better discussed using cognition rather than computational programs.

  • Purpose itself can be viewed as an evolutionary innovation like minds, developing with the first true organisms and present in single-celled life. Purpose can exist without minds but minds may require purpose.

  • Biology struggles with agency since it can’t systematically address how it arises. Definitions of life struggle to identify necessary/sufficient attributes, but agency may be the fundamental feature shared by all living things.

  • Even non-Darwinian adaptation is possible if correlations with environments allow more efficient energy absorption, as complex systems tend to settle into well-adapted states.

  • England and colleagues developed a theoretical model showing how nonequilibrium systems can self-organize into configurations that maximize their ability to absorb energy from fluctuating environmental forces and dissipate entropy, without the need for Darwinian natural selection.

  • Their model demonstrates that particles jostled by the energy of their surroundings will tend to adopt oscillatory patterns that are resonant with and correlated to the driving frequency, maximizing energy absorption and dissipation.

  • This results in self-organized, ordered structures rather than disorder, driven purely by thermodynamic principles rather than intentional planning by the particles.

  • Darwinian evolution can be seen as a specific case of this more general physical principle of environmental attunement through ordered structure. Replication allows especially well-adapted states to emerge.

  • Biology is aided by but not determined by physics. It leverages useful non-equilibrium, self-organized, and information-based physical processes without being reducible to physics alone. Understanding life may require accounting for agency according to physical principles.

  • One motivation of the Human Genome Project was to create a genetic database for medical research. As genome sequencing becomes cheaper, it’s possible to identify gene variants associated with diseases.

  • Many common diseases like heart disease and diabetes are polygenic, involving hundreds of genes with small statistical effects. Gene therapies would be difficult for these. Personalized medicine based on risk predictions also has limitations due to environmental influences.

  • While identifying disease-linked genes through GWAS studies has been successful, this information alone is not usually enough to develop new treatments. Understanding the functional consequences of genetic mutations is also needed.

  • In some cases linking diseases to genes has led to new drugs, like drugs that target the proteins CTLA4 and IL6R to treat rheumatoid arthritis. But for most common diseases, genetics provide limited insights into causes or cures. Personalized medicine based on genetics also faces challenges from biased genomic databases and polygenic influences.

In summary, genetics research through genome sequencing and GWAS has had some successes but also limitations in developing new disease treatments or making personalized medicine a reality, due to most diseases having complex, polygenic nature influenced by environment as well. Deeper functional understanding is often still needed.

  • Genetic studies have had limited success in identifying new treatments, as the identified genes are often not the direct drug targets or causal factors. Unraveling the exact causal links has been challenging.

  • Most disease-linked variants from GWAS studies are in non-coding regulatory regions, influencing gene expression rather than encoding proteins. Understanding these complex regulatory mechanisms is needed to develop interventions.

  • Even monogenic diseases like sickle cell anemia and cystic fibrosis involve multiple genetic and non-genetic factors interacting, not just a single gene. The actual disease is a physiological phenomenon.

  • Sex determination involves multiple genes like SRY, Sox9 and SF1 interacting, not just SRY alone. Factors other than genes, like hormones, can also influence sexual development.

  • In general, genes are one of many factors influencing health, and disease manifests at the physiological level of tissues/organs, not just at the genetic level. The genome provides an incomplete picture and does not predict outcomes on its own. Understanding multiple layers of biological information is needed for effective genetic medicine.

  • Development and phenotypes are influenced by signaling molecules like hormones, not just genes/chromosomes. Sex development can produce ambiguous or intersex traits.

  • Disease symptoms often result from various triggers activating a limited set of physiological response pathways. This “canalization” means different diseases can share symptoms.

  • Research is exploring common molecular mechanisms hijacked across diseases like cancer, Alzheimer’s, and COVID. Targeting shared vulnerabilities may apply to multiple conditions.

  • Physiological responses like blood cell counts follow similar trajectories in recovery from diverse acute illnesses, suggesting deep equivalence in underlying processes.

  • While specifics matter, there may be generic cell/tissue responses that intersect multiple diseases. More cross-disease dialogue could aid drug discovery.

  • COVID drugs highlighted limitations of “magic bullet” approach - conditions may share causal roots amenable to repurposed drugs, not just specific targets. Canalization supports drug repurposing across ostensibly unrelated diseases.

  • The human body has innate and adaptive immune systems that work together to defend against pathogens. The innate system provides a quick first response, while the adaptive system develops targeted responses through antibodies and cells.

  • The immune system must balance defending the body while avoiding harming healthy cells. It uses various cells and molecular signals to identify threats and mount an appropriate response.

  • An excessive immune response, like a “cytokine storm”, can cause organ damage as seen in severe COVID-19 cases. Our understanding of immune dynamics is still incomplete.

  • The immune system is interconnected with other bodily systems and a key determinant of overall health. Conditions like heart disease, obesity, and even mental health have immune links.

  • Targeting the physiological response, like inflammation, has proven an effective strategy for treating some diseases. Dexamethasone reduced COVID mortality by damping excessive immune reactions.

  • A unified view of health should consider the immune system’s critical role in defending the body from diverse threats in a coordinated, adaptive way. Its complexity surpasses even the brain.

  • Amyloid beta protein (Aβ) forms plaques in the brain that are toxic to neurons and associated with Alzheimer’s disease. The risk of misfolding and plaque formation increases with age.

  • Some people inherita dominant mutation in the APP gene that virtually guarantees they will develop early-onset Alzheimer’s in their 40s-50s.

  • Promising treatments aim to clear amyloid plaques using immunotherapy to help the immune system attack the plaques, similar to vaccines. Clinical trials are testing passive immunization treatments.

  • A possible link has been proposed between gum disease bacteria like P. gingivalis and Alzheimer’s, as the bacteria have been found in Alzheimer’s patient brains and can induce Alzheimer’s-like symptoms in mice. This links a neurological disease to dental health via the immune system.

  • Some researchers want to develop “digital twins” using real-time physiological monitoring and predictive modeling to track health status, predict responses, and help guide treatment for conditions like Alzheimer’s or pandemics. This could transform medicine from reactive to preventative.

  • Persistent issues remain for some cancers like brain, liver and pancreatic cancers despite progress increasing survival rates for other cancers like breast and prostate. Cancer increasingly appears to be an inevitable consequence of multicellular life rather than a strictly pathological disease.

  • Cancer cells are often thought of as genetic mutations gone wrong, but this view has limitations. Decades of focusing on genetic causes of cancer have yielded little in treatment advances.

  • Other cellular processes like apoptosis (programmed cell death) and tumor suppressor genes actually exist to prevent cancer by repairing DNA damage or killing cells when damaged. Mutations in these genes may lead to cancer by disrupting their protective functions.

  • Looking just at genetic mutations misses important context - the type of cell, its environment, neighborhood interactions, developmental origins, etc. Cancer arises from an interaction between mutations and this cellular context.

  • Cancer cells are still regulated like normal cells and not completely “selfish”. Tumors resemble deranged tissue development more than a mass of uncontrolled growth. Single-cell analysis shows tumors contain diverse cell types, not just one cancer cell.

  • Multicellularity requires cells to moderate growth, but reverting to a more primitive individual state is an “inevitable attractor” given by cellular nature. Cancer reveals how precarious cooperation is and how cells might naturally favor unrestrained growth.

  • In summary, cancer is better viewed as a problem of tissue organization and development than a genetic disease of rogue cells, and cures require understanding the system-level context not just genetic drivers.

  • Previous studies had found that brain tumors (glioblastomas) usually expressed one of four distinct cancer cell types, suggesting four classes of tumor requiring different treatments.

  • Bernstein’s single-cell analysis found that tumors usually contained all four cell types in varying proportions, with only the dominant type seen when studying the whole tumor.

  • These cell types arise from differentiation of cancer “stem cells” akin to normal stem cell differentiation, though tumor cells get stuck in a proliferative state.

  • Tumors seem to follow developmental plans to interface with the host, resembling organ development and tissue regeneration.

  • Tumors can repurpose normal cells like fibroblasts and reprogram cells like neurons to promote growth and metastasis, making treatment difficult.

  • Cancer cells are unusually plastic, transitioning between states more readily than normal cells, conferring an evasion advantage against single-targeted therapies.

  • A new approach called “differentiation therapy” aims to guide cancer cells back to a non-malignant state, inspired by stem cell reprogramming, with some promising early results in leukemia.

  • While promising, curing cancer may require targeting the physiological disruption of metastasis that actually causes mortality, rather than just eliminating tumor mass. A higher-level causal perspective is needed.

  • Researchers are developing new ways to engineer and shape living matter by directly manipulating genetic code and biological systems. This allows designing organisms not shaped by evolution.

  • Early work included growing tissues in labs and inducing parthenogenesis in sea urchins. The discovery of DNA’s structure enabled genetic engineering by cutting and splicing DNA.

  • CRISPR-Cas9 gene editing greatly increased precision and expanded engineering possibilities. Researchers are producing drugs and teaching cells new metabolic pathways through genetic changes.

  • Synthetic biology aims to systematically redesign organisms through engineered genetic circuits and pathways, like producing fuels in yeast factories. The goal is engineering life at a sophisticated, systematic level.

  • Researchers have created synthetic gene circuits that control bacterial blinking and densities. Some aim to fully map and engineer simple model organisms to serve as platforms for biological devices and reprogramming life. This turns traditional views of natural design on their head.

  • In 2010, researchers at JCVI (J. Craig Venter Institute) created the first self-replicating bacterial cell controlled by a synthetic genome. They constructed artificial DNA for a Mycoplasma mycoides bacterium from scratch and “booted up” cells with this new DNA, which functioned normally.

  • The goal was to verify that bacterial cells can work with simplified, redesigned genetic instructions to gain a better understanding of bacterial genomes and life’s essential functions. In 2016, JCVI described a “minimal” Mycoplasma genome.

  • Synthetic biology raises issues like enhanced pathogens escaping control. Researchers are exploring safeguards like self-destruct mechanisms or dependencies on non-natural substances. However, anticipating all problems will be difficult as capabilities grow over decades.

  • While synthetic biologists can redesign bacteria by reengineering genomes, eukaryotic cells are more challenging due to complexity. Early work focuses on simple systems like yeast or engineering mammalian transcription circuits to achieve multiple cell states.

  • Achieving desired phenotypes through genetic design is likely intractable except for simple traits, due to the lack of direct genotype-phenotype mapping. An empirical, trial-and-error approach may be needed to fine-tune cellular self-organization rather than rational design.

  • Engineered Living Systems (ELS) takes a developmental biology approach to synthetic biology, aiming to steer cell development rather than directly engineer genes. This involves tweaking the chemical, mechanical and electrical signals cells use to communicate and direct each other’s growth.

  • Understanding the basic rules that govern how multicellular organisms develop their form and body plans is important for ELS. Cells coordinate via signaling networks to balance “bottom-up” genetic factors and “top-down” organism-level influences.

  • This process gives rise to a “morphospace” of possible stable forms, only some of which evolution has explored. ELS aims to discover novel shapes and organisms by adjusting cell signaling parameters.

  • Organoid research reveals cells’ inherent ability to self-organize. Stem cells cultured in vitro can develop organized tissue structures like miniature organs through cell communication. This provides insights into development and disease modeling.

  • Organoids are an example of morphological engineering, as their form depends on growth conditions. Their plasticity demonstrates the mutability of developmental principles and possible organismal forms within the constraints of cellular capabilities.

  • Researchers are able to manipulate stem cells and growth conditions to grow organoids and tissues outside the body in ways not seen in normal embryonic development. This opens up new morphological possibilities.

  • Scientists have grown synthetic embryo models using mouse stem cells that organize into structures resembling early embryos, going through gastrulation and forming rudimentary organs. Similar models could be made with human cells.

  • These synthetic embryos raise philosophical and ethical questions as their development may not follow normal trajectories and their long-term potential is unknown. Regulations around human embryo research may not neatly apply to them.

  • Chimeric embryos combining cells from different species also show developmental processes are more flexible than previously thought. They challenge ideas of fixed species boundaries and developmental blueprints.

  • Experiments producing “xenobots” from frog stem cells revealed entirely new life forms are possible through self-assembly of cells under different conditions than normal development. This suggests the wide morphospace of what cells and developmental rules can produce.

  • Researchers took skin cells from frog embryos and separated them, observing their behavior. First they gathered together as expected, but then unexpectedly began swimming around by coordinating their beating cilia.

  • These cell clusters, called xenobots, displayed complex behaviors like navigating mazes and responding to their environment. They also communicated to each other via calcium signaling.

  • Xenobots were able to regenerate from damage and could survive for over 90 days with proper nutrients, much longer than normal.

  • Their formation seems guided by collective goals of the cells like minimizing surfaces and responding to the environment. They maintain their integrity and boundaries.

  • Xenobots challenge traditional definitions of life and classification. They represent a new type of organism defined by behavior rather than lineage.

  • They could provide insights into how multicellular life first emerged and the basic rules of biological self-organization from cells.

  • Researchers want to further understand the rules governing how cells collectively develop shapes and structures, which is a more complex engineering problem than simple assembly. Both top-down positioning and bottom-up self-assembly may be involved.

  • There are two main approaches to building multicellular engineered living systems (MCELS) - a top-down approach where cells are precisely positioned, and a bottom-up emergent approach where cells are programmed to self-assemble into the desired structure.

  • The bottom-up approach could produce more robust structures that cells can sustain and repair themselves, but it is challenging to reliably generate and predict outcomes.

  • Tools like optogenetics, mechanical manipulation, thermal and electrical stimulation could help guide cell differentiation and self-assembly in a bottom-up way. Computer simulations may be needed to predict how cells will interact.

  • Researchers are using engineered living tissues like muscle as actuators in robotic devices, allowing novel behaviors compared to artificial materials. An example is a “jellyfish robot” that swims using rat heart muscle tissue.

  • Entire cell-based robots called xenobots have been created by shaping frog cells into computer-designed configurations that can move in an organized way.

  • As cell-based engineering progresses, it may require a new collaborative mindset between engineers and the intrinsic intelligence of living materials. The goal would be autonomous systems that recognize high-level goals through negotiation rather than precise design. This could blur traditional distinctions between machine, robot and organism.

The passage discusses how synthetic biology and engineered life forms may allow us to develop new forms of life and new ways of thinking. Through designing new morphologies and traits, we could go beyond just imagining “life as it could be” to envisioning “minds as they could be.”

It then talks about how use of the word “gene” in digitized texts has peaked around the time of the Human Genome Project according to analysis of word frequencies (culturomics). While this data reveals trends, more work is needed to truly understand why usage may be declining. Linguistic patterns can hint at deeper cultural and scientific changes happening.

The passage argues that life is complex and cannot be fully understood by looking just at its basic components like genes. It requires examining the multifaceted interactions between an organism and its environment, as well as higher-level structures and causality. Analogizing life to language, it notes that words alone do not convey meaning - context is crucial. Ultimately, life works through relationships and depends on ascribing significance or “meaning” to its interactions, just as language and literature do for humans.

  • Multicellular organisms needed new ways to handle information and make autonomous decisions beyond just genetic hardwiring, in order to coordinate complex biological systems. Even simple prokaryotes have some degree of cognition in their molecular networks.

  • Eukaryotes took this further by integrating multiple information sources, improvising responses, reconciling conflicts, and making contingent decisions with limited information - tasks familiar to humans but which predated nervous systems.

  • Life has evolved to rely less on genes for actual functioning by delegating responsibilities like decisions, maintenance and behavior to higher organizational levels like cognition. Genes still influence behaviors long-term through natural selection but can’t dictate everything.

  • Humans take this the furthest with complex cultures that pass on information between generations non-genetically. But cognition in any organism can produce non-adaptive behaviors by nature of being an improvised response system.

  • This points to a more creative view of evolution that has discovered many ways to generate life beyond what early theories envisioned. A new framework is needed to account for both component and systemic perspectives on an equal footing.

  • Evolutionary biology has often focused narrowly on genes and genomes, viewing them as a blueprint that simply needs to be “read out” to create an organism. However, development is influenced by many levels beyond just genes.

  • Small changes at the genetic level, like tweaks to gene regulation, can produce significant phenotypic differences. Regulation plays a major role in shaping development.

  • Examples from studies of human brain development and butterfly wing patterns show how regulatory changes can drive evolutionary changes, not just changes to core genes.

  • Development is shaped by higher-level principles like cell interactions and morphogen gradients, creating a “morphological landscape” of possibilities. Evolution selects among these possibilities rather than directly building forms.

  • Cadherin cell adhesion proteins may have enabled the origins of multicellular animals by allowing single-celled colonies to take on 3D “liquid tissue” forms via generic physical forces.

  • A wider, more integrated view of genes, development and evolution is needed to truly understand how evolutionary change happens in complex organisms beyond just allele frequencies. Evolvability and robustness are also important evolutionary properties to consider.

  • The passage discusses how developmental mechanisms ensure coordinated changes to anatomical structures during evolution, like keeping the lower beak proportionate to changes in the upper beak or head size in birds. A single signaling molecule (BMP protein) influences the whole beak size.

  • This buffering provided by higher levels of biological organization, like development, reduces the likelihood that genetic changes will be lethal. It also allows small genetic changes to have significant impacts on phenotypes through regulatory pathways.

  • Kirschner and Gerhart argue organisms have a “core system” in their genomes that provides the basic ingredients for anatomical development across animals through a developmental “toolkit.” This is robust due to weak regulatory linkages and allows new patterns of regulation.

  • This core developmental system is highly conserved between species as changes would be disastrous. Evolution occurs through tweaking around the edges. Evolvability requires coherent reproducing entities, like cells, that have hierarchical organization to absorb unexpected changes.

  • The passage discusses how the modern synthesis view makes organisms passive, while others argue organisms actively shape their environments and evolution through agency. This brings up questions about whether organismal agency could generate directionality in evolution through attractors.

  • The author spoke to experts at Harvard about biology and found that most felt the actual details and understanding of how life works was worse than feared. It is difficult to find accounts that fully explain phenomena like gene function, cell behavior, and what makes life special.

  • No simple narratives exist and disagreements are common. The author aims to provide better metaphors or narratives than commonly used ones, though acknowledges limitations.

  • Writing this book was a challenging task given the complexity and lack of clear answers in biology. General statements are difficult without disagreement.

  • The author is grateful to various people at Harvard who helped make the visit and writing of the book possible, including key discussions that provided inspiration and perspective.

  • Key challenges mentioned are the lack of coherence or patterns when examining biological details, and the fact that few questions seem to have simple answers as experiments conflict and views differ. The book aims to probe deeper into the workings of life despite these difficulties.

Here is a summary of the quotes provided:

  • Geddes 2022 suggests thinking of modern biology as aiming to understand life’s organization and how it arises.

  • Jacob 1973 calls the organization of life the “second secret of life”.

  • Rosen 1991 says throwing away the organization of life misses the key problems.

  • Monod 1977 refers to the organization of life as the “second secret of life”.

  • Itoh et al. 2007 suggests the emergence of animals involved novel organizational features.

  • Jacob 1977 says novelties come from previously existing organizational features.

  • Balcerak et al. 2019 discusses observations of organizational principles in cells.

  • Keller 1995 notes early promises of a linear structure to development underestimated its organizational complexity.

  • Bray 2009 refers to protein complexes associated with organizational features in cells.

  • Personal communications from researchers like Spakowitz, Tjian, and Brangwynne discuss organizational features and principles in cells and development.

  • Shin and Brangwynne 2017 introduce the concept of liquid phase condensation as an organizational feature in cells.

  • Other comments note organizational features conferring robustness, parallels to neural networks, how organization shapes cell behaviors, and the emergence of organization during evolution.

In summary, the quotes discuss the importance of understanding organizational features and principles in living things from various levels, from cells to development to evolution, and how this has challenged early linear views of biology. Personal communications also reflect on developments in this area.

Here is a summary of the key points about signal perception in the BMP signaling pathway from the referenced paper:

  • BMP signaling plays an important role in patterning tissues during embryonic development by regulating cell differentiation.

  • The BMP pathway is activated when BMP ligands (growth factors) bind to heterotetrameric transmembrane serine/threonine kinase receptors on the cell surface.

  • This leads to phosphorylation of receptor-regulated Smads (R-Smads), namely Smad1, Smad5, and Smad8. The phosphorylated R-Smads then complex with the common mediator Smad4.

  • The Smad complexes accumulate in the nucleus and regulate gene transcription by interacting with DNA-binding transcription factors and chromatin regulators. This influences expression of target genes that drive cellular responses.

  • Precise signal perception by the receiving cells is required for appropriate transcriptional responses and downstream biological outcomes. The levels and duration of R-Smad phosphorylation are thought to encode signaling intensity and response specificity.

  • The paper discusses various mechanisms by which cells spatially and temporally control BMP signal transduction, including regulation of receptor complexes, R-Smad phosphorylation kinetics, nuclear import of Smads, and interaction of Smads with chromatin. Fine-tuning of these processes is important for accurate signal perception and decoding in the BMP pathway.

Here is a summary of the passages from ch 20:982–93 of the source text:

This section discusses several aspects of patterns, processes and systems in developmental biology. It touches on topics like symmetry breaking in early embryonic development, using stem cell models to study embryogenesis, epigenetic regulation as an important aspect of development, exploring structural heterogeneity across cell lines, endogenous tagging techniques to map cellular organization, pattern formation via a segmentation clock in biofilms, amyloid aggregation induced by viruses in human cerebrospinal fluid, debates around engineering synthetic and chimeric organisms, accounting for noise/stochasticity in developmental patterning mechanisms, the importance of non-coding regions in gene regulation and more. Overall it provides a high-level overview of several key recent advances and open questions across various subfields related to developmental and cellular biology from the perspective of self-organization, patterning, regulation and modeling.

This passage summarizes findings from the journal article “Compensation of changes in cell size by adjustment of cell number and cell shape in heteroploidy salamander larvae” published in the Journal of Experimental Zoology in 1953.

The key points are:

  • The article studied salamander larvae with abnormal chromosome numbers (heteroploidy).

  • It found that when cell size changed due to heteroploidy, the larvae compensated by adjusting cell number and cell shape.

  • Specifically, increases in cell size were counterbalanced by decreases in cell number, while changes in cell shape also helped maintain normal organ structure when cell numbers were altered.

  • This demonstrated the larvae’s ability to regulate overall organ size and structure even when individual cell characteristics changed due to chromosomal abnormalities.

  • The study provided early evidence that developing organisms can compensate for disruptions at the cellular level through coordinated changes in other cellular properties.

Here are summaries of the papers:

    1. “Quantifying causal emergence shows that macro can beat micro.” Proceedings of the National Academy of Sciences of the USA 110:19790–95. This paper proposes that emergent macroscale phenomena can outperform microscopic description and prediction in complex systems. It presents a framework to quantify causal emergence.
  • Hoel, E., et al. 2020. “Evolution leads to emergence: An analysis of protein interactomes across the tree of life.” This preprint analyzes protein interaction networks across species and finds that evolution leads to the emergence of new organizational properties at higher biological scales.

  • Hoel, E., and M. Levin. 2020. “Emergence of informative higher scales in biological systems.” This paper develops a computational framework for optimal prediction and control at emergent higher scales in biological systems.

  • Hopwood, N. 2022. “‘Not birth, marriage or death, but gastrulation’: The life of a quotation in biology.” This examines the history and usage of the famous quote about the importance of gastrulation in development.

  • Hove, J. R., et al. 2003. “Intracardiac fluid forces are an essential epigenetic factor for embryonic cardiogenesis.” This Nature paper shows fluid forces in the embryonic heart tube are an essential epigenetic factor for cardiogenesis.

  • Howe, J., et al. 2022. “Multicellularity in animals: The potential for within-organism conflict.” This PNAS paper discusses the potential for conflict between individual cells and the needs of the multicellular whole.

Here is a summary of several key papers by developmental biologist M. Levin:

  • Levin argues that biological systems can be understood as dynamic networks of collaborative molecular agents that interact and collectively self-organize. This perspective emphasizes distributed control and causal agency throughout living systems.

  • His work explores how gene regulatory networks, cell-cell communication via bioelectricity and mechanotransduction, and extracellular matrix interactions enable tissues and organisms to respond adaptively to environmental cues.

  • Levin proposes that development and regeneration involve reprogramming cellular networks to achieve anatomical homeostasis. Computational modeling aims to understand how localized interactions scale up to coordinate global responses.

  • His research investigates left-right patterning in embryogenesis, planar cell polarity, regenerative control mechanisms in planarians, and factors influencing regeneration competence across species.

  • Later papers discuss implications for understanding biological causation, cognition in living systems, principles of self-organization and autonomy in development, and the relationship between embodied agents and established developmental mechanisms.

  • Levin argues for conceptualizing organisms as modular, plastic cognitive agents capable of flexible responses to environmental information via bidirectional interactions between genomes, proteomes and socio-material contexts.

Here is a summary of the provided references:

The references cover a wide range of topics related to biology, genetics, and epigenetics. Some key themes covered include:

  • Cellular differentiation and reprogramming (Morris and Daley 2013, Newman 2020)

  • Mechanisms of inheritance beyond DNA, including epigenetic inheritance (Morgan et al. 1999)

  • Molecular mechanisms like gene regulation by non-coding RNAs (Morris and Mattick 2014)

  • Developmental biology concepts like patterns formation, left-right asymmetry (Müller et al. 2012, Nakamura et al. 2006)

  • Systems/evolutionary perspectives on biological organization and form (Newman 1992, 2019, 2020; Morowitz and Smith 2007)

  • Philosophical discussions of reductionism, mechanisms, machine analogies in biology (Nicholson 2013, 2018; Moss 2003)

  • Broader impacts and discussions of genetics research (Nelkin and Lindee 1995; Nerlich et al. 2002)

  • Single cell approaches and cell-to-cell variability (Pelkmans 2012; Perkel 2021a)

  • Applications of principles to bioengineering and synthetic biology (Pascalie et al. 2016; Park et al. 2016)

In summary, the references cover a broad range of topics related to genetics, molecular and developmental biology, systems/evolutionary perspectives, and philosophical analyses from leading researchers in the field.

Here is a summary of the key points from the papers:

  • Ang, X. H. 2021a. Discusses how multiomics analysis, which integrates multiple types of biological data (e.g. genomics, epigenomics, transcriptomics, proteomics), is entering a new age due to advances in technology allowing for high-throughput measurement.

  • Ang, X. H. 2021b. Notes that proteomics, the study of proteins, is now able to be done at the single-cell level due to improvements in techniques like mass spectrometry.

  • Perunov, N., R. Marsland, and J. England. 2016. Examines statistical physics approaches to understanding adaptation and evolution on a molecular level.

  • Petridou, N. I. et al. 2021. Finds that rigidity percolation, a concept from statistical physics, can help uncover mechanisms underlying embryonic tissue phase transitions.

  • Pezzulo, G. et al. 2020/2016. Discusses top-down, systems-level models in biology and argues they are needed to explain phenomena above the molecular level, like regeneration and development.

So in summary, the papers discuss advances that are enabling multi-omics analysis at single cell resolution, and the potential for statistical physics concepts to provide insight into biological phenomena like development, evolution and phase transitions.

Here is a summary of the key points from the provided papers:

  • larized microRNA regulation and its implications in human cancers (Scientific Reports 7:13356): This paper investigates the spatial expression patterns of miRNAs in tissues and their role in establishing gradients that impact cancer progression. They find miRNAs exhibit expression gradients that contribute to tissue patterning and deregulation of these gradients may promote cancer.

  • Bending gradients: how the intestinal stem cell gets its home (Cell 161:569–80): This paper examines how bending of the intestinal epithelium creates spatial gradients that guide intestinal stem cell positioning and differentiation. Mechanical forces and signaling gradients work together to ensure proper tissue architecture.

  • OCT4 acts as an integrator of pluripotency and signal-induced differentiation (Molecular Cell 63:647–61): This study looks at the role of transcription factor OCT4 in balancing stem cell pluripotency and differentiation in response to signaling cues. OCT4 precisionally regulates genes to enable plastic interconversion between states.

  • Embryoids, organoids and gastruloids: New approaches to understanding embryogenesis (Development 144:976–85): This review summarizes recent advances in generating 3D tissue models from stem cells that emulate aspects of early development, including embryoids, organoids and gastruloids. These models provide new tools for studying embryogenesis.

In summary, the papers discuss spatial gradients in tissues that guide processes like stem cell positioning, differentiation, and tissue patterning during development and how disruptions to these gradients can contribute to diseases like cancer. They also assess new in vitro models that aim to emulate early embryonic development.

Here are summaries of the three papers:

Warmflash, A., et al. (2014) This paper describes a new method for recapitulating early embryonic spatial patterning in human embryonic stem cells in vitro. The method allows researchers to study processes like gastrulation and axis induction outside of a living embryo. This could help provide insights into early human development and how disruptions can lead to diseases.

Watson, J. D., et al. (1987) This is the fourth edition of the book Molecular Biology of the Gene by James Watson, Nicholas Hopkins, James Roberts, Joan Steitz, and Alan Weiner. The book provides a comprehensive overview of molecular biology and genetics for researchers and students. It covers topics like DNA structure and replication, RNA transcription, protein synthesis, gene regulation, and genetic engineering.

Yamanaka, Y., et al. (2022, preprint) This preprint paper reports on reconstituting human somitogenesis, the process of somite formation, in vitro. Somites are embryonic structures that give rise to vertebrae, ribs, and muscles. The researchers developed a culture system modeling early embryonic developmental processes. They observed formation of somite-like segmented structures, providing insights into somitogenesis and its roles in patterning the developing body plan.

  • Ion, genes, immune system, integrity, life, life’s processes, linguistics, organization, and transcription are all discussed in relation to cells and their various functions and properties.

  • Avery, Baltimore, Bateson, Beadle, Bernard, Berzelius, Binet, and others are mentioned in relation to early discoveries and theories in biology and genetics.

  • Bacteria, bacterial flagellar motor, bacterial reproduction, biofilms, internally organization are discussed. Viral interactions with bacteria also mentioned.

  • Biochemistry, cell biology, developmental biology, and molecular biology concepts are introduced in relation to genes, proteins, interactions, signaling, development.

  • Cancer, genes, genetics, apoptosis, therapies, and research are covered in relation to cells and organism development going awry.

  • Cells are discussed at length as fundamental units - all cells coming from cells, as factories, building blocks, agency, complexity, cognition, communication, cycles, differentiation, diversity, division, defects. Stem cells, epiblasts, hypoblasts also covered.

  • Developmental concepts like patterning, morphogenesis, gastrulation, EMT covered in cell context. Cytoskeleton, signaling pathways, networks, compartments introduced.

  • Overall it provides an overview of foundational biological concepts and early scientists through the lens of cells - their functions, properties, roles in development, relations to genes, proteins and systems.

Here is a summary of the key points about cells from the passage:

  • Cells are the basic unit of structure and organization in living organisms. They contain organelles like the nucleus, mitochondria, lysosomes, etc. enclosed within membranes.

  • Cells undergo various types of cell division like mitosis and meiosis to multiply and develop into different cell types. Cell specialization leads to different cell lineages and tissue/organ formation.

  • Cells communicate with each other via signaling molecules and organize spatially within tissues and organisms through cell-cell interactions, polarity, and migration.

  • Cell types include stem cells, immune cells, nerve cells, muscle cells, pigment cells, etc. Stem cells are unspecialized and can differentiate into various cell types.

  • Cells contain DNA within the nucleus which provides instructions for cell functioning. Chromosomes contain genes and regulate the expression of proteins and other molecules that carry out cell functions.

  • Organs and organisms arise from networks of cellular interactions. Cell behavior emerges from molecular components and interactions within the cell and with other cells. Cells display properties of self-organization, adaptation and response to environmental cues.

  • Cells can be reprogrammed and studied individually using techniques like single-cell mapping and synthetic biology approaches. Understanding cells provides insights into development, physiology, disease and potential applications in regenerative medicine.

Here is a summary of the key points about genes and DNA from the passage:

  • Genes are made of DNA and contain the instructions for making proteins and controlling cellular functions. DNA consists of double helix strands made of bases (A, C, G, T).

  • Genes are located on chromosomes within the nucleus of cells. They can be activated or deactivated by epigenetic factors like methylation.

  • DNA replication allows genes to be passed from parent cells to daughter cells. DNA damage or errors during replication can introduce mutations in genes.

  • Genes code for traits like eye color by coding for specific proteins. They also interact with the environment and can have different effects depending on circumstances through gene expression.

  • Genes evolve over generations through processes like natural selection. Environments can drive changes in gene frequencies in populations. Gene expression and epigenetics can also evolve.

  • DNA sequencing has revealed that only a small portion of DNA directly codes for proteins, while much is non-coding DNA with regulatory functions. Projects like ENCODE have shed light on this “junk” DNA.

  • Genes influence complex traits and behaviors through interactions in biological pathways and networks, not isolated effects. They contribute to development, differentiation and inheritance of characteristics.

  • Genes encode proteins, are made of DNA, and contain the instructions for building an organism and regulating its functions. They are the basic physical units of heredity and work together in complex networks and pathways.

  • Genetics research has shed light on the genetic basis of traits and diseases. Many genes and gene variants have been identified that influence conditions like breast cancer, cystic fibrosis, and more.

  • Development is regulated by gene expression and protein interactions. Key genes involved in development include homeobox genes, signaling molecules, transcription factors, and others. Mutations can disrupt development and cause defects.

  • The genome contains not just protein-coding genes but also regulatory elements, noncoding RNAs, and other sequences that influence gene regulation and expression. Genome-wide association studies have mapped regions linked to traits.

  • Genetic engineering and gene therapies aim to manipulate genes to treat diseases, while CRISPR-Cas9 provides a powerful new tool for editing genomes. The field of epigenetics studies how gene expression is regulated independent of DNA sequences.

  • Summing up, genes are the basic units that carry out life’s functions through protein synthesis and regulation via complex gene networks, genomes encode this genetic information, and research is advancing our understanding of inheritance, development, disease causation, and potential applications.

  • Tests on pages 86-87 and 264 discuss experimental work related to the topic.

  • The Island of Doctor Moreau by H.G. Wells is referenced on page 413.

  • Ivermectin is discussed in footnote 4 on page 394 in relation to its medical uses.

  • Eva Jablonka is cited on page 436 in relation to her work on evolutionary processes.

  • François Jacob is referenced multiple times (pages 6-7, 28, 40n10, 97-98, 113-14, 153-56, 175, 227, 228, 418-19, 457-58) in relation to his contributions to developmental biology, genetics, and evolution.

  • Johannes Jaeger is cited on pages 363, 452-53, 458-60 in relation to his work on evolutionary theory and systems biology.

  • The J. Craig Venter Institute is discussed on pages 419-20 in relation to synthetic biology research.

  • Jellyfish and comb jellies are discussed on pages 43 and 219-20, 441-42 in relation to their biology and potential applications to robotics.

Here is a summary of the key points about molecular biology from the passage:

  • Molecular biology involves studying genes, genetics, DNA, RNA, proteins and their interactions at the molecular level. It examines the Central Dogma of biology which outlines how genetic information flows from DNA to RNA to proteins.

  • Important events in the history of molecular biology include the discovery of the DNA double helix structure by Watson and Crick in 1953, and subsequent research establishing DNA as the genetic material and deciphering the genetic code.

  • Molecular biology explores how genes encode proteins and how organisms inherit genetic traits from their parents. It also examines how proteins, RNA and molecules interact and work together within cells and organisms.

  • Areas of ongoing research in molecular biology include developing a deeper understanding of the molecular interactions, networks and pathways that drive biological processes at the cellular and whole organism levels. It is an interdisciplinary field that integrates concepts from genetics, biochemistry, and other biological sciences.

  • In summary, molecular biology examines life at the molecular level, focusing on understanding the roles and interactions of DNA, RNA, proteins and other biomolecules that make up genetic information and carry out the functions of living things. It seeks to explain biological phenomena through molecular mechanisms and genetic principles.

Here is a summary of the key points about 60n6:

  • Plasticity is a core property of biological forms and living matter. It allows for flexibility, change, development and reversibility. Plasticity occurs at various levels including genetic influences, cell fate, tissues, shapes and regulatory networks.

  • Intrinsic disorder, which refers to flexible and irregular protein structures, is crucial for plasticity and functionality. Many proteins have disordered regions that allow for interaction with other molecules.

  • Morphological principles can change and evolve over time through plasticity at the genetic, cellular and systems levels. This allows organisms to adapt to new environments and challenges.

  • RNA regulation plays an important role in plasticity by controlling gene expression patterns and responding dynamically to stimuli. RNA molecules like microRNAs fine-tune regulatory networks.

  • The passage discusses how plasticity underlies developmental processes and allows organisms to change their form, adaptive shapes and cell fates depending on genetic and environmental factors throughout life. This flexibility and adaptability is a hallmark of living systems.

Here is a summary of the key points from the provided section:

  • The passage discusses the gene known as the “H Gene” or homeobox gene, which is important for body pattern formation and development.

  • Homeobox genes were discovered by Edward Lewis, which helped elucidate the genetic control of embryogenesis. They code for homeodomain proteins that act as transcriptional regulators.

  • Mutations in homeobox genes can lead to homeotic transformations, where one body part takes on the appearance of another (e.g. legs growing where antennae should be).

  • The conserved homeodomain sequence within these genes helped reveal the shared ancestry of animal body plans and homology of animal structures.

  • The passage discusses experiments in the early 1980s by Gehring and colleagues on fruit flies that helped characterize homeobox genes and their influence on development.

  • It provides more context on homeobox genes between pages 95-96 and 99-102, as well as referencing them again on page 371 in the context of evolution and development of animal body plans.

So in summary, the key idea is that the passage discusses the important homeobox or “H Gene” which plays a role in embryonic development and body pattern formation through its transcriptional regulation functions. It provides historical and experimental context surrounding the discovery and characterization of these influential genes.

  • The passage discusses Robert Hooke’s idea from 1826 that plant cells either occur singly or are united together to form greater or smaller masses to form more highly organized plants.

  • It notes that the origin of the phrase “every good regulator of a system must be a model of that system” is unclear, though it is often attributed to pioneering cyberneticists Arturo Rosenblueth and Norbert Wiener.

  • Metaphors in biology tend not to be universally applicable and can obscure limitations. Carl Zimmer’s 2020 book Life’s Edge provides one of the most comprehensive surveys of how scientists have defined life.

  • Michael Levin argues the category of cognitive entities, not just living things, can “have a point.” But currently there are no known truly cognitive non-living entities.

  • Analogies between life and computation are limited, as neural networks can learn in ways resembling living things, but this does not mean life is computation.

  • The biologist J. B. S. Haldane expressed the relationship between biologists and teleology as like a mistress - not admitted publicly but impossible to live without.

  • The passage discusses nature, evolution, genetics, and development from the perspective of avoiding overly simplistic or reductionist views. There are few neat, self-contained stories in biology.

  • Influences on development come from both genes and environment in an integrated way that is difficult to disentangle. Evolution, natural selection, and random genetic drift also interact in complex ways.

  • Concepts like “genes,” the basic unit of heredity, have proven fuzzy given new discoveries like regulatory elements, non-coding RNA, and the fluid composition of structures like the ribosome.

  • Analogies and metaphors used in biology must be treated cautiously, as the realities are often more intricate than any analogy can capture. For example, there is no single “book of life” but rather diverse interacting components.

  • The passage encourages an open-minded approach that acknowledges gaps in current understanding and does not assume any division of the genome, cellular processes, or influences on development are truly discrete or well-defined. Integrated, multidimensional perspectives are needed.

In short, the key point seems to be advocating for nuanced, complex interpretations that avoid overly simplistic or reductionist views in understanding biology, evolution and development. Flexible, evidence-based thinking is important given our still-limited knowledge.

  • The Earth creates a tiny wobble in the Sun’s position due to their center of gravity being close to the Sun’s center. This wobble can be more significant for larger planets like Jupiter, and astronomers use these wobbles to detect exoplanets.

  • In C. elegans nematode worms, each cell has a precisely specified type and location, suggesting a “blueprint” view of development. However, most other species have much less specific development, so C. elegans is an unrepresentative example. The rules governing mammalian development come from somewhere other than just the genome.

  • Reconfigurable computing allows electronic devices and connections to actively alter to suit computational tasks, similarly to how living things adapt - another example of machines echoing life.

  • Jennings was an early 20th century thinker who speculated presciently about “chemical packets” in paired strings like DNA double helix, though he didn’t fully understand it. He had progressive views on race for his time but was also a eugenicist.

  • The chapter discusses early embryonic studies in chickens by Aristotle and the formation of germ layers and mesoderm in development. It notes the roles of various signals and transcription factors.

  • The HIF1α gene becomes up-regulated in low-oxygen conditions. Understanding how cells sense and respond to oxygen availability won the 2019 Nobel Prize in physiology or medicine.

  • Researchers have proposed that left-right asymmetry in embryos is established before cilia involvement, due to an inherent cytoskeleton twist. Cilia may then amplify the initial asymmetry.

  • Some non-motile cilia were found to act as mechanical sensors of left-right fluid flow, converting it to chemical signals guiding development.

  • We don’t actually know which aspect of zebras (stripes) favors their circumstances - suggestions include camouflage, thermal regulation, fly deterrence but evidence is limited.

  • Death seems abrupt and irreversible despite revival being sometimes possible, with the main change being loss of life itself.

  • Some ecosystems are sustained by energy from deep Earth released through hydrothermal vents in oceans.

  • Schrödinger was discussing macroscopic but not microscopic motion continuing randomly.

  • In 2022, Trinity College renamed a Schrödinger lecture theater due to evidence he was a pedophile.

  • Evidence was emerging for DNA as the genetic material even as Schrödinger wrote, through Avery’s bacterial experiments.

  • Quasicrystals, discovered in 1984, have ordered yet non-repeating atomic structures defying symmetry laws.

  • The chapter discusses the history and criticisms of synthetic biology, including concerns about “playing God” by engineering life. Early pioneering work was done by scientists like Yoshiki Sasai, who developed brain organoids, though he later died by suicide after a misconduct scandal.

  • Craig Venter’s team sparked controversy when they spoke of engineering synthetic cells in 2007. Some synthetic biologists avoid terms like “create” to distance from religious connotations.

  • Recent research led by Hanna has grown mouse embryos in a rotating incubator for up to half their gestation period. While most IVF embryos don’t develop fully, this shows the potential of the technique.

  • There is a distinction between sheep-goat chimeras with mixed cell lineages, versus hybrids from cross-species breeding which have a single genome.

  • Brain organoids grown from human cells have shown potential intelligence by learning games like Pong faster than AI algorithms, and responding to neural signals with muscle twitches. So synthetic organs may develop rudimentary brain-like functions.

  • The epilogue notes ongoing debates about the historical figure of Homer and acknowledges that while genes correlate with behaviors, they do not solely cause them.

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