August Weismann rejected the inheritance of acquired characters on the grounds that changes to the soma cannot produce the kind of changes to the germ-plasm that would result in the altered character being transmitted to subsequent generations. His intended distinction, between germ-plasm and soma, was closer to the modern distinction between genotype and phenotype than to the modern distinction between germ cells and somatic cells. Recently, systems of epigenetic inheritance have been claimed to make possible the inheritance of acquired characters. (...) I argue that the sense in which these claims are true does not challenge fundamental tenets of neo-Darwinism. Epigenetic inheritance expands the range of options available to genes but evolutionary adaptation remains the product of natural selection of ‘random’ variation. (shrink)

Abstract Gene-selectionists define fundamental terms in non-standard ways. Genes are determinants of difference. Phenotypes are defined as a gene’s effects relative to some alternative whereas the environment is defined as all parts of the world that are shared by the alternatives being compared. Environments choose among phenotypes and thereby choose among genes. By this process, successful gene sequences become stores of information about what works in the environment. The strategic gene is defined as a set of gene tokens that combines (...) ‘actor’ tokens responsible for an effect with ‘recipient’ tokens whose replication is thereby enhanced. This set of tokens can extend across the boundaries of individual organisms, or other levels of selection, as these are traditionally defined. Content Type Journal Article Pages 1-19 DOI 10.1007/s10539-012-9315-5 Authors David Haig, Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA Journal Biology and Philosophy Online ISSN 1572-8404 Print ISSN 0169-3867. (shrink)

Organisms can be treated as optimizers when there is consensus among their genes about what is best to be done, but genomic consensus is often lacking, especially in interactions among kin because kin share some genes but not others. Grafen adopts a majoritarian perspective in which an individual’s interests are identified with the interests of the largest coreplicon of its genome, but genomic imprinting and recombination factionalize the genome so that no faction may predominate in some interactions among kin. Once (...) intragenomic conflicts are recognized, the individual organism can be conceptualized as an arbiter among competing interests within a collective. Organismal adaptation can be recognized without phenotypes being optimized. (shrink)

Most eukaryotes possess many copies of rDNA. Organismal selection alone cannot maintain rRNA function because the effects of mutations in one rDNA are diluted by the presence of many other rDNAs. rRNA quality is maintained by processes that increase homogeneity of rRNA within, and heterogeneity among, germ cells thereby increasing the effectiveness of cellular selection on ribosomal function. A successful rDNA repeat will possess adaptations for spreading within tandem arrays by intranuclear selection. These adaptations reside in the non‐coding regions of (...) rDNA. Single‐copy genes are predicted to manage processes of intranuclear and cellular selection in the germline to maintain the quality of rRNA expressed in somatic cells of future generations. (shrink)

Mitochondria exist in large numbers per cell. Therefore, the strength of natural selection on individual mtDNAs for their contribution to cellular fitness is weak whereas the strength of selection in favor of mtDNAs that increase their own replication without regard for cellular functions is strong. This problem has been solved for most mitochondrial genes by their transfer to the nucleus but a few critical genes remain encoded by mtDNA. Organisms manage the evolution of mtDNA to prevent mutational decay of essential (...) services mitochondria provide to their hosts. Bottlenecks of mitochondrial numbers in female germlines increase the homogeneity of mtDNAs within cells and allow intraorganismal selection to eliminate cells with low quality mitochondria. Mechanisms of intracellular “quality control” allow direct selection on the competence of individual mtDNAs. These processes maintain the integrity of mtDNAs within the germline but are inadequate to indefinitely maintain mitochondrial function in somatic cells. (shrink)

The germ track is the cellular path by which genes are transmitted to future generations whereas somatic cells die with their body and do not leave direct descendants. Transposable elements (TEs) evolve to be silent in somatic cells but active in the germ track. Thus, the performance of most bodily functions by a sequestered soma reduces organismal costs of TEs. Flexible forms of gene regulation are permissible in the soma because of the self‐imposed silence of TEs, but strict licensing of (...) transcription and translation is maintained in the germ track to control proliferation of TEs. Delayed zygotic genome activation (ZGA) and maternally inherited germ granules are adaptations that enhance germ‐track security. Mammalian embryos exhibit very early ZGA associated with extensive mobilization of retroelements. This window of vulnerability to retrotransposition in early embryos is an indirect consequence of evolutionary conflicts within the mammalian genome over postzygotic maternal provisioning. (shrink)

Organisms and their genomes are mosaics of features of different evolutionary age. Older features are maintained by ‘negative’ selection and comprise part of the selective environment that has shaped the evolution of newer features by ‘positive’ selection. Body plans and body parts are among the most conservative elements of the environment in which genetic differences are selected. By this process, well-trodden paths of development constrain and direct paths of evolutionary change. Structuralism and adaptationism are both vindicated. Form plays a selective (...) role in the molding of form. (shrink)

Concepts of cause, choice, and information are closely related. A cause is a choice that can be held responsible. It is a difference that makes a difference. Information about past causes and their effects is a valuable commodity because it can be used to guide future choices. Information about criteria of choice is generated by choosing a subset from an ensemble for ‘reasons’ and has meaning for an interpreter when it is used to achieve an end. Natural selection evolves interpreters (...) with ends. Surviving genes embody a textual record of past choices that had favorable outcomes. Consultation of these archives guides current choices. Purposive choice is well-informed difference making. (shrink)

RNAs can do many things. They can store information, act in the world, and respond to the world. Because of these capabilities biologists have proposed a primordial ‘RNA world’ in which RNA, rather than DNA, performed the central role of replicator and repository of adaptive information. Deacon dismisses this hypothesis because replication is not about anything and because the structure of replicating molecules cannot contain information about the environment. I dispute both claims. An RNA and its opposite-sense complement represent each (...) other and, by two rounds of complementation, represent themselves. Although nucleic acid sequences do not change in response to their present environment, these sequences embody information about ancestral environments via the selective filtering of alternative sequences in those environments. Nucleic acid sequences are the textual record of what has worked in the past. (shrink)

David Haig propounds and illustrates the unity of a radically revised set of definitions of the family of terms at the heart of philosophy of cognitive science and mind: information, meaning, interpretation, text, choice, possibility, cause. This biological re-grounding of much-debated concepts yields a bounty of insights into the nature of meaning and life. An interpreter is a mechanism that uses information in choice. The capabilities of the interpreter couple an entropy of inputs to an entropy of outputs is dispelled (...) by observation. The second entropy is dispelled. I propose that an interpreter’s response to inputs meaning of the information for the interpreter. In this conceptual framework, the mechanisms of interpreters provide the much-debated link between Shannon information and semantics. (shrink)

A gene is described as imprinted if its pattern of expression depends on whether it passed the previous generation in a male or female germ line. A recent paper(1) reports that imprinted genes have fewer and smaller introns than a control set of genes. The differences are striking but their interpretation is unclear. The loss of introns after a gene becomes imprinted is not sufficient to explain why imprinted genes have fewer introns than average, because related unimprinted genes also have (...) few introns. Similarly, small introns appear to be a property of chromosomal region rather than of imprinting status itself, because neighboring unimprinted genes also have small introns. (shrink)

Imprinted genes are predicted to affect interactions among relatives. Therefore, variant alleles at imprinted loci are promising candidates for playing a causal role in disorders of social behavior. The effects of imprinted genes evolved in the context of patterns of asymmetric relatedness that existed within social groups of our ancestors.

Transformations of Lamarckism is an edited volume arising from a workshop to commemorate the bicentenary of the publication of Philosophie Zoologique. The contributed chapters discuss the history of Lamarckism, present new developments in biology that could be considered to vindicate Lamarck, and argue for a revision, if not a revolution, in evolutionary theory. My review argues that twentieth and twenty-first century conceptions of Lamarckism can be considered a reaction to August Weismann’s uncompromising rejection of the inheritance of acquired characters in (...) the late nineteenth century. Weismann rejected the inheritance of acquired characters both as a proximate mechanism of heredity and as an ultimate cause of adaptation. I argue that Weismann’s proximate claim is still valid for the kind of mechanism that he had in mind but that the inheritance of acquired characters has come to refer to many different processes, some of which undoubtedly do occur. However, processes of physiological adaptation and adaptive plasticity, even if transgenerational, do not challenge Weismann’s claim about the ultimate causes of adaptation because these processes can be understood as evolving by natural selection. Finally, I discuss some of the emotional and aesthetic reasons why many find Lamarckism an attractive alternative to hard-core neo-Darwinism. (shrink)

Homologous centromeres compete for segregation to the secondary oocyte nucleus at female meiosis I. Centromeric repeats also compete with each other to populate centromeres in mitotic cells of the germline and have become adapted to use the recombinational machinery present at centromeres to promote their own propagation. Repeats are not needed at centromeres, rather centromeres appear to be hospitable habitats for the colonization and proliferation of repeats. This is probably an indirect consequence of two distinctive features of centromeric DNA. Centromeres (...) are subject to breakage by the mechanical forces exerted by microtubules and meiotic crossing‐over is suppressed. Centromeric proteins acting in trans are under selection to mitigate the costs of centromeric repeats acting in cis. Collateral costs of mitotic competition at centromeres may help to explain the high rates of aneuploidy observed in early human embryos. (shrink)

In the Sleeping Beauty problem, Beauty is woken once if a coin lands heads or twice if the coin lands tails but promptly forgets each waking on returning to sleep. Philosophers have divided over whether her waking credence in heads should be a half or a third. Beauty has centered beliefs about her world and about her location in that world. When given new information about her location she should update her worldly beliefs before updating her locative beliefs. When she (...) conditionalizes in this way, her credence in heads is a half before and after being told it is Monday. In applications of Dutch Book arguments to the Sleeping Beauty problem, the probability of a particular outcome has often been confounded with consequences of that outcome. Heads and tails are equally likely but twice as much is at stake if the coin falls tails because Beauty is fated to make the same choice twice. As a consequence, the possibility of tails should be given twice the weight of the possibility of heads when deciding whether to bet on heads even though heads and tails are equally likely. (shrink)

Proximate and ultimate causes in evolutionary biology have come to conflate two distinctions. The first is a distinction between immediate and historical causes. The second is between explanations of mechanism and adaptive function. Mayr emphasized the first distinction but many evolutionary biologists use proximate and ultimate causes to refer to the second. I recommend that ‘ultimate cause’ be abandoned as ambiguous.