The Fate of Darwinism: Evolution After the Modern Synthesis
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- Depew, D.J. & Weber, B.H. Biol Theory (2011) 6: 89. doi:10.1007/s13752-011-0007-1
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We trace the history of the Modern Evolutionary Synthesis, and of genetic Darwinism generally, with a view to showing why, even in its current versions, it can no longer serve as a general framework for evolutionary theory. The main reason is empirical. Genetical Darwinism cannot accommodate the role of development (and of genes in development) in many evolutionary processes. We go on to discuss two conceptual issues: whether natural selection can be the “creative factor” in a new, more general framework for evolutionary theorizing; and whether in such a framework organisms must be conceived as self-organizing systems embedded in self-organizing ecological systems.
KeywordsDevelopmental Systems TheoryEcological systemsGenetical DarwinismHierarchical expansion (of synthesis)Modern Evolutionary SynthesisNatural selectionNiche constructionSelf-organizationSelfish gene theory
Darwinism as a Research Tradition: Five Points
Charles Darwin claimed that all species on earth have descended from a common ancestor. In one sense of the term, Darwinism refers to this discovery—the discovery of species diversification from a single point of origin. In another and more proper sense, however, Darwinism refers to its author’s proposed causal explanation of evolution—natural selection—and to theories in which this process plays the dominant role in evolution, including human evolution. The second is the sense in which the term will generally be used in this article.
Our first claim is that Darwinism considered as a theory of descent with modification from a common ancestor by means of the differential retention of heritable variations, i.e., natural selection, would probably have gone the way of other grand nineteenth century ideologies or “meta-narratives” if it had not been turned in the first half of the twentieth century into a mathematized science. In this respect, Darwinism’s fate contrasts with that of two other seminal nineteenth and early twentieth century discourses, Marxism and Freudianism. Nineteenth century Darwinism was at least as laced with ideology as they. It may not have sanctioned capitalist class warfare, as Marxists, semi-Marxists, and leftist liberals have alleged in their talk about “social Darwinism,” but at times it undeniably comforted racists, sanctioned imperialism, and actively promoted eugenics.1 Still, strenuous efforts by Marxists and Freudians to cast their discourses as scientific ultimately failed while those of Darwinians succeeded. The insights of Marxists and Freudians both ended up in the toolbox of humanists. Darwinism, shed of eugenics, imperialism, and racism, became mathematized, scientific, and in some ways more humanistic than the post- or anti-humanism into which Marx’s and Freud’s legacies have devolved.
This claim leads to a second. The fact that Darwinism’s scientific credentials have proven to be more secure than those of rival evolutionary traditions—Lamarckism, for example, or saltationist mutationism—explains why it remains to this day the dominant research tradition in evolutionary biology. These rival traditions had pre-Darwinian antecedents, but under Darwinism’s influence they embraced common descent after 1859. What they rejected was the power of natural selection. Many notions favored by these rival traditions are empirically true enough. Nonetheless, it is largely because Lamarckism, saltationist (sudden) mutationism, and inner-driven orthogenesis, to name the most enduring alternative traditions in evolutionary biology, failed to become mathematized empirical sciences with at least a foothold on value-neutrality that Darwinism still rules the evolutionary roost.
This point lends poignancy to our third claim, which is the leitmotiv of this article. Darwinism in its current scientific incarnation has pretty much reached the end of its rope. By “current incarnation” we are referring specifically to the Modern Evolutionary Synthesis, whose formative period stretched from about 1940 to 1970. More generally, however, the impasse extends to the “population genetical theory of natural selection” that a decade or so earlier had reconciled very small genetic mutations as the source of variation with natural selection considered as the cause of its non-random spread (Fisher 1930). Population-genetic Darwinism generally, as well as the Evolutionary Synthesis that applied it to standing issues in historical biology—speciation, paleontology, biogeographical distribution of species, systematic classification of taxa, community ecology, and so forth—and several emendations of the Synthesis that adapted it to molecular genetics all shifted from development to the changing genetic composition of populations as the focus for identifying variation and the discriminate process of sorting it that is natural selection. This reframing at the level of populations made it possible for Darwinism to appeal to the mathematics of probability in measuring mutation rates, selection pressure, and other so-called evolutionary “forces,” such as genetic drift, in ways toward which Darwin himself could only gesture. Sometimes, but rather improperly, called “neo-Darwinism,” it is not only the Modern Synthesis, but population genetical Darwinism more generally, that we are claiming has reached the end of its dominance.2
Let us be clear about what this means. We are not saying that the population-genetical theory of natural selection will not remain adequate for a range of problems, much in the same way that Newtonian physics, suitably re-described and limited in its scope, works well enough for middle-sized objects exchanging middle-range energies in middle-sized time frames. The issue is whether the Darwinism of the Modern Synthesis and its successor programs, notably Selfish Gene Theory and its rival, the Hierarchically Expanded Modern Synthesis, can continue to present itself as a general theory of biological evolution. We are claiming that it cannot.
Let us be clear, too, that in saying this we are not saying that Darwinism as such is on its deathbed. Here, we reach a fourth point. The impending demise of various articulations of the genetical theory of natural selection does not in the least imply that the entire Darwinian research tradition is on the verge of failure. The Darwinian research tradition, as we have argued extensively elsewhere, has in the past shown an uncanny ability to remake itself in the face of factual discoveries that undermined earlier versions of the theory of natural selection but did not prevent new versions from emerging that proved to be more mathematically powerful even as they showed themselves to be more factually adequate (Depew and Weber 1995; Weber 2007). We would be the last to suggest that Darwinism can’t reform and reframe itself yet again.
This is an important point. When Darwinism’s complex conceptual and discursive history is ignored, critiques of one or another of its many articulations tend to present themselves as falsifications of Darwinism as such. This is just what is wrong with What Darwin Got Wrong, a book recently addressed to the public by Fodor and Piattelli-Palmarini (2010). As their title suggests, Fodor and Piattelli-Palmarini make little distinction between Darwin and genetical Darwinism. They may have shown that there are many evolutionary phenomena that the latter does not explain. But they also feel entitled to help themselves to the large conclusion that Darwinism as such is dead. They do so because they fail to recognize that in the past, improved versions of Darwinism have taken the place of inadequate ones and that a new version—a Darwinism of the future—may well displace population genetical Darwinism without ending, but instead enriching, Darwinism as such.
If Darwinism does manage to refashion itself to accommodate facts presented to it by contemporary biology and what lies ahead, we want to suggest that it will do so in a way not unlike its earlier reformulations. The transition from nineteenth to twentieth century Darwinism was accomplished by applying dynamical models taken from statistical mechanics and thermodynamics to the distribution of genotypes in populations (Depew and Weber 1995). The transition from twentieth to twenty-first century Darwinism is, we claim, already making use of models of the dynamics of complex systems to articulate a new general theory, or at least a framework for one. That will be our fifth, and our most speculative, point.
Genetic Darwinism in Five Acts
Our purpose in this section is to sketch the history of genetical Darwinism from its beginnings at the turn of the twentieth century with a view to showing why at the beginning of the twenty-first century it has come up against its limits. We will portray this history as a play in five acts.
Act 1: Natural Selection Contra Mutation
The story begins with validation of adaptive natural selection as an actual natural phenomenon beginning in the 1880s. This was accomplished by the British “biometricians,” led by Walter Weldon, Francis Galton, and Karl Pearson. They used statistical analysis to prove that changes in populations under environmental shifts—shifts such as the silting up of a bay or, in work done much later, the blackening of trees due to industrial pollution—could not be a matter of chance, but only of increased rates of reproduction due to the beneficial effects of identifiable variations.
At first, this solidly empirical work was opposed by advocates of saltationist mutationism, who noted that the biometricians’ adaptationist scenarios—the silting up had caused a sub-population of crustaceans with widened mouths to increase its numbers because their mouths were less clogged with silt; dark moths predominated over light-colored because they were harder for prey to see on the blackened bark of trees—did not touch the process of speciation. According to mutationists like Hugo De Vries and William Bateson it is large but fortuitous variations that managed such leaps. The recovery of Gregor Mendel’s proof that inheritance comes in combinable units (soon called “genes”) gave backing to their conclusion.
Act 2: Mutation Plus Natural Selection
An intermediate position that can be justly called Darwinian became popular in the first three decades of the twentieth century. It assigned the creative role in evolution to sudden mutations. To natural selection, it assigned only the housekeeping work of filtering out unfit mutations. The result was adaptedness by elimination. After a struggle, however, the biometrical theory of natural selection was integrated with Mendelian genetics by mathematical demonstrations, based on probability theory, showing that small genetic changes can be added up over trans-generational time into genuine adaptedness (see Provine 1971). In this case, natural selection is not just the editor but the creator of adaptedness and adaptations. According to this view, some phenotypic traits, as well as the organisms that possess them and, with the organisms, the genotypes that “code for” them, will spread disproportionately through populations across trans-generational time because these traits and the genetic variations that undergird them have reproductive advantages that can be seen at the population but not at the individual level, where it is impossible to distinguish between chance and fitness. All this was the work of population-genetical theorists led by Ronald Fisher, Sewall Wright, J. B. S. Haldane, and Sergei Chetverikoff. Taken collectively, their work and that of their successors defines the population-genetical theory of natural selection.
In this second act, statistical reasoning functions not only as a measure of natural selection (as opposed to a null hypothesis of change by chance in the distribution of genotypes and phenotypes), as it did for the biometricians as well, but as actually defining the formal objects or entities over which the genetical theory of natural selection ranges. These objects are populations of interbreeding organisms. The model on which proof of this proposition was based was adopted from statistical mechanics and statistical thermodynamics. Genotypes, like molecules of a gas, have an equilibrium distribution (the Hardy–Weinberg equilibrium formula). They can be thrown out of this equilibrium by “forces” such as mutation, selection, genetic drift, density-dependence, or gene flow across population boundaries. These forces are exerted by phenotypic differences that are themselves results of genotypic differences. Phenotypic advantages thus go hand-in-hand with the increased spread of the genes that code for them. Hence, observable traits recur in greater proportions in successive generations if the genotypes that cause them are heritable. Hence, too, proclaimed Fisher (1930), the rate of adaptive natural selection in a population is directly proportional to the amount of trans-generationally additive heritable genetic variation available in that population. Genetic variation, in other words, is the fuel of natural selection and natural selection, not mutation as such, is the actual cause over multiple generations of states of relative adaptedness in populations and of adaptive traits in organisms that are members of those populations.
Act 3: The Modern Synthesis
The third act in our drama is about how the population-genetical theory of natural selection as we have just described it became the foundation of the Modern Evolutionary Synthesis of the 1940s–1960s. It did so by applying population-genetical theory to the problems of working field naturalists, especially speciation, adaptive radiation, and the process of divergence from which taxa at and above the species level evolve. The aim of the Modern Synthesis, thus, was to interpret the population-genetical theory of natural selection by mapping the mathematics of genotype changes onto the spatial and temporal distributions of traits, organisms, cooperating groups, species, and other lineages with a view to solving these and other biological problems (Lewontin 1974).
The pioneers and practitioners of the Modern Synthesis, notably Theodosius Dobzhansky, Ernst Mayr, Julian Huxley, and George Gaylord Simpson, worked in different but largely compatible ways. (They clashed, but only occasionally, and were generally committed to maintaining a common front.) In contrast to their mathematical predecessors, they all favored the causal primacy of matches or mismatches between environments and phenotypes, noting that even the best genotypes can make it across the generational bottleneck only if they succeed at the phenotypic level. They differed, however—sometimes even with their former selves—about whether speciation, for example, is adaptive or at least initially results from genetic drift, i.e., the accidental preservation of genes in small “founder” populations (Wright 1931). The mathematical formalisms that all adherents of the Modern Synthesis shared make both scenarios possible. Those whose interpretive habits were more “adaptationist,” however, favored selection, while those who suspected that adaptationism contains too many echoes of the natural theological “design argument” tended to favor the work of chance in the initial phase of the speciation process.
Inquiries along these lines led to new methods of classifying organisms. In general, classification on an evolutionary background is to be a branching picture of descent in accord with Darwin’s prescription. The Modern Synthesis made great progress on this subject. Throughout most of its history, however, room was usually left for value-laden “grades” as well as for ancestor-descendent “clades” or branches (Huxley 1942; Mayr 1942; Simpson 1944). Since grades inevitably contain traces or echoes of the ancient and medieval “great chain of being” that is deeply embedded in the “folk ontology” of the West, moving entirely to “cladism” by completely eliminating the notion of higher and lower that is reflected in the concept of evolutionary grades is still very much in process. This ongoing shift has not reached the ears of popular culture at all, but it is among the most solid results of the Modern Synthesis. Ironically, it is a result that, because of the fidelity of the Synthesis to the notion of evolutionary grades, leads beyond its boundaries.
For all its limitations, the greatest beauty of the Modern Synthesis is that it gave substance to Darwinism’s claim to be value-free science by providing decisive reasons for rejecting Darwinism’s prior association with racism, imperialism, and eugenics. It did so by reformulating natural selection in ways that do not depend except in extreme conditions on Malthusian competition for scarce resources or on casting natural selection in the role of executioner of the presumably unfit. Fitness now means little more than what it is mathematically measured by: comparative descendent contribution or reproductive success in sub-populations. Elimination of the unfit because of certain stereotyped characteristics disappears even as a concept. Selection will occur whenever there is a gradient—another concept taken from thermodynamic models—between the availability of genetic variation and the differential abilities of organisms possessing this variation to utilize environmental resources.
The version of Modern Synthesis that flourished in the post-World War II era had a good scientific as well as a moral reason to distance itself from eugenics. The moral reason is that Nazism had discredited eugenics. The scientific reason is that variation, as Dobzhansky (1937, 1970) and his students showed, is abundant in natural populations. Nor is it concentrated at good and bad ends of a distribution curve, as eugenicists (including Fisher) had presumed when they argued that people at the good end (perhaps measured by IQ) should marry each other and those at the bad should be sterilized. Genetic variation is plentiful and ubiquitous (Lewontin 1974).
Given these facts about the distribution of variation, natural selection can be presented as even more creative than the founders of the Modern Synthesis had initially believed. Small, trans-generationally accumulated genetic changes keep populations tuned to environments that they themselves are constantly degrading. The best way of staying tuned to environments that are constantly changing is to evolve adaptations for adapting. Rather than merely preserving organisms that are for a time molded to environments, accordingly, natural selection favors the emergence of traits that enable organisms to modify their environments to maintain their life-activity (Lewontin 1983, 2000; Odling-Smee et al. 2003). Culture, with its ability to reconstruct environments by the transmission of learned behaviors, including economic techniques, is a magnificent instance of such an evolutionary innovation (Dobzhansky 1962). It would seem from this point of view that so-called social Darwinism, eugenics, and, as we will see, sociobiology and evolutionary psychology, have in common too thin a theory of culture—our biological inheritance according to these views is always bubbling up to thwart us—to recognize the true significance of this evolutionary innovation.
Unfortunately, however, the powerful discourse of the Modern Synthesis, at once mathematical and humanistic, failed to be absorbed intact into public sphere discussions and so failed to change the dog-eat-dog image of Darwinism that had long before been fixed in the age of ideology. Perhaps it was too technical. Although it was introduced into school curricula in the 1960s, perhaps it was badly taught. However that may be, the recrudescence of creationism in some countries must be construed as marking the inability of the Modern Evolutionary Synthesis, in spite of considerable effort, to affect how Darwinism is understood by the public (Depew 2010a).
Act 4: Molecular Darwinism
So much for the first three acts in the history of genetic Darwinism conceived after the fashion of a five-act play. The fourth act is about the effect on population genetical Darwinism of molecular genetics beginning in the 1950s and 1960s. The Modern Synthesis was up and running before Francis Crick and James Watson discovered the mechanism for generating genetic variation in the beautiful structure of DNA in 1953. The founders of the Synthesis were nervously enthusiastic about this discovery (Mayr 1959; Dobzhansky 1964). They were enthusiastic for two good reasons. First, until then the term “gene” did not have a fully concrete material referent. Indeed, it had begun life as a purely theoretical postulation. Molecular genetics solved that problem by identifying genes as very concrete entities—stretches of DNA that are transcribed into RNA and then translated into protein and stretches that start and stop this process at various points in the developmental process. The second reason they had for feeling relief was that this discovery corroborated and even confirmed theoretical population genetics by supplying its missing piece—the ultimate source of variation in the predictable and inevitable error rate in DNA replication.
Nonetheless, the owners and operators of the Modern Evolutionary Synthesis were also nervous about molecular genetics. For one thing, molecular geneticists had no background in evolutionary inquiry. They were biochemists (Judson 1979). Perhaps for this very reason Crick and Watson, who in virtue of their discoveries quickly became gurus of the new molecular biology, propounded a “greedy reductionist” philosophy of science that threatened to put evolutionary naturalists out of business by rewriting population genetics as molecular genetics, thereby proving that life is “nothing but” chemistry. In response, the surviving makers of the Modern Synthesis became stout defenders of the “autonomy” of evolutionary biology from the clutches of the molecularists (Mayr 1988). They were successful in doing so to the extent that they pointed out that biological systems are inherently hierarchically structured and for this reason are so full of emergent properties and processes that they are related to the molecular mechanics of the gene only in extremely complex ways—ways that might be understood by experienced field naturalists, but would forever elude the grasp of molecular experimentalists (Mayr 1988). Still, the founders remained nervous because they knew in their hearts that the population-genetical core of the Modern Synthesis depended on an expectation that molecular genetics would never turn up any facts that belie its basic principles. From the outset, this expectation was little more than a hope.
Throughout the 1970s and 1980s, molecular biology pulled the Modern Synthesis in two directions, sparking controversies severe enough to undermine efforts by Mayr and other pioneers to present a single front to the public, thereby raising both its interest and its suspicions.3 Roughly, theorists who were sympathetic to the agency of organisms in dealing with their environments embraced hierarchically expanded versions of the Synthesis (Gould 1982, 2002). These allowed natural selection to operate at various levels of the biological hierarchy—nuclear, cellular, organismic, group, and even species—and permitted the various “forces” of mutation, selection, genetic drift, and gene flow to affect these levels differently. Those on the other hand who relied on replication errors to generate the appropriate mutations for adaptively affecting gene frequencies opted to contract the Synthesis to what was happening at the level of genes in order to accommodate and take advantage of the molecular revolution in genetics. They gave agency to the genes and took it away from organisms.
Among gene-centered interpretations, Richard Dawkins’s well-known “selfish gene” hypothesis stands out (Dawkins  1989). This hypothesis proposed to reduce the potential conflict between molecular and population genetics by reformulating the Modern Synthesis from a gene’s-eye point of view. According to Dawkins, DNA makes as many copies of itself as it can simply because that is what (allegedly) self-replicating molecules like DNA do. Genes are stretches of DNA that stick together through meiotic division by being translated into proteins that fold up to make cell types and tissue. These make phenotypes and the organisms that bear them. Some phenotypes enable the organisms that carry them to interact with environments in ways that reproductively outcompete others. This has the effect of increasing the representation of the genes that code for these more effective phenotypes. This “genocentric” model favors natural selection over other “forces” and accordingly assumes that most traits are adaptations. This “empirical adaptationism” is the Modern Synthesis all right, but it is a version of it that assigns not only causal but directional force to the inherent more-making capacity of “selfish genes.”
Selfish gene theory was able to gain prestige by offering ingenious and yet simple explanations for several phenomena that in the late 1960s and early 1970s had been shown to exist, but not to fit particularly well into the orthodox version of the Synthesis. One of these phenomena occurs at the basic level of molecular evolution, the other at the opposite level of social evolution. At the lower level, selfish gene theorists could explain why point mutations in DNA sequences accumulate at a predictable, though imperfectly regular, rate without any evidence of having been naturally selected or having adaptive value (neutral mutation, the evolutionary clock hypothesis). That’s just what DNA, left to its own devices, can be expected to do, Dawkins contended. That is why there is (or is alleged to be) so much non-coding “junk DNA” in genomes.
At the higher social level, selfish gene theory was impressive to many because it explained the phenomenon of “kin selection,” which in turn explained the standing problem of how cooperative phenomena in social insects (and other taxa, including primates) could possibly arise in a Darwinian, that is, a basically competitive, world.4 From a gene’s eye perspective, selfish gene theorists pointed out, it matters not at all how many genetically related bodies are useful in maximizing self-replication. If the cooperative phenotypes of genetically related individuals yield higher rates of replication then selection will favor them. People as well as ants might be altruistic, then—but only if their genes are selfish. By the end of the twentieth century selfish gene theory had become the public face of Darwinism, its advocates slyly suggesting that Gould’s hierarchically expanded interpretation was really not Darwinian at all because it rejected adaptationism and gradualism (Dennett 1995).5
Why, we may ask, was selfish gene theory able to present itself as the mature culmination of the Modern Synthesis and to do so far more persuasively than had earlier, organism-centered and multi-level versions? The main reason, we suspect, is that selfish gene theory features notions of selfishness and competition that the public had long associated with Darwinism. (Most people are only vaguely aware that selfish gene theory is an explanation, not a denial, of altruism; for Dawkins it is genes, not organisms, that are selfish.) If one goes on to ask why selfish gene adaptationism has become popular not only as a new form of “pop Darwinism,” but also among natural and social scientists, who can be presumed to know better, we think the answer is that its focus on genes as discreet causal, and hence technically manipulable, entities made genocentric adaptationism safe for medical, agricultural, and other forms of biotechnology (Depew 2003). In fact, what has happened is that continual advances in genetic technoscience have been accompanied by an appreciation for Darwinian adaptationism that it has seldom, if ever, enjoyed before.
This approach involves, however, an entirely speculative account of human evolution. Selfish gene theory, like most adaptationist versions of the Modern Synthesis, sees organisms as assemblies of relatively discreet adaptations. Accordingly, it has been favored by cognitive and behavioral scientists, who like to portray mental states as supervening on a set of functionally dedicated modules localized in specific parts of the brain. Natural selection, according to the argument of so-called evolutionary psychologists, evolved these adaptations, many of which tend to naturalize traditional gender roles, at an early period in human history (Barkow et al. 1992). Like its predecessor, sociobiology, evolutionary psychology has encouraged dissemination of the selfish gene version of the Modern Synthesis to the public as a way of connecting the social to the biological sciences in a quasi-reductionist manner aimed at justifying oft-frustrated hopes for a genuinely scientific, biologically grounded theory of human evolution.
It should be noted, however, that the research programs of sociobiology and evolutionary psychology are in considerable tension with the efforts of pioneers of the Modern Synthesis, notably Dobzhansky (1962), to construe human beings as having evolved culture as an adaptive, plastic, flexible capacity that trumps specific adaptations that are too closely tied to specific environments to be anything other than evolutionary dead ends. Evolutionary psychology has, accordingly, distressed Dobzhansky’s intellectual heirs because it casts doubt on the treasured claim that human culture, in the sense pioneered by Franz Boas, is an outcome of natural selection for enhanced plasticity of response to changing environments. Because it replaces the autonomy of culture with a set of discrete adaptations that were at their most functional in bygone Pleistocene environments, and so are to some degree at odds with modern life, it seems to heirs of the Synthesis in its heyday as well as to advocates of an “expanded” Synthesis like Gould that, wittingly or no, the alliance between molecular biologists and selfish gene theory has let in through the backdoor traces of the racism, sexism, eugenical thinking, and other ideological distortions from which the Modern Synthesis strove so hard in its formative years to dissociate Darwinism (Lewontin 1992).
Act 5: The End of Population Genetic Darwinism
We now reach act five of our drama. Here, as in any good play, we encounter ironic recognitions and sudden reversals. The story involves the Human Genome Project (HGP) and other gene sequencing projects that were initially funded by governments in the late 1980s and then taken up by private enterprise. These projects were grounded in highly genocentric, molecularist assumptions about evolution. Like selfish gene theory, ardent advocates of sequencing the human genome as well as the genomes of the fruit fly, mouse, flatworm, and other model species typically construed organisms as collections of discreet adaptations, each of which is “read out only” from segments of genomes conceived as instruction manuals, blueprints, or computer programs for making organisms. Connected as they were to promises about genetic medicine, which, it was supposed, would eventually enable doctors to identify genes gone bad and replace them like burnt-out light bulbs, the HGP raised expectations for cures of inherited diseases in the public mind that were greeted with great suspicion by evolutionists with organism-centered views as well as by ecologists, developmental biologists, and clinicians, who understood the complexity and sensitivity of this process in ways that genetic technologists frequently did not.6
Perhaps the most prophetic skeptic was the historian of science Evelyn Fox Keller. She urged the HGP to go forward knowing full well that genome sequencing would empirically turn up, much to the surprise and chagrin of its advocates, a relation between genes and phenotypic expressions so complex that it would unequivocally refute once and for all the reductionistic assumptions built into the hypothesis on which the HGP was launched. We will learn to cease talking about “gene action,” Keller (2000a, b) argues, as if genes are autonomous and controlling agents, and learn to talk instead about “gene activation” in ways that accord at least as much agency to organisms and their interactions with environments.
There is probably very little “junk DNA.” The entire genome, including its frequent repeats, plays a role in regulating gene expression (Pink et al. 2011).
Coding segments of RNA are not entirely faithful in their transcription from DNA (Li et al. 2011).
Changes in sectors of the genome that initiate and stop protein production in the course of development are important in initiating rapid evolutionary changes that are correlated with and responsive to environmental change (Colosimo et al. 2004).
Mutations in promoter and enhancer gene segments are only one source of developmental variation. Some phenomena that occur in the epigenetic (developmental) process, including chemical marking of DNA by methyl groups, are heritable in even the strictest sense (Jablonka and Lamb 1995, 2005, 2010).
In bacteria and other elementary life forms, mutation rates increase under stress and might even be directional (Foster 2004).
Much of the genome, including regulatory sectors, is highly conserved across surprisingly divergent clades. Genes such as Homeobox, for example, which undergirds segmentation and bilateral symmetry, form part of a relatively compact but very ancient metazoan “tool kit” from which indefinitely different kinds of organisms can be made (see Gilbert and Epel 2009). For this reason, estimates of how many genes humans possess have gone down from about 100,000 to about 30,000, almost none of which is distinctively human.
Regulatory genes express themselves very differently in different contexts. The cellular environment, which is itself open to influences from the wider environment, can affect the timing, placement, and rate at which enhancers and promoters go to work making enzymes and other structural gene products. This makes for wider “phenotypic plasticity” than even organocentric interpretations of Modern Synthesis posited and a fortiori far more plasticity than its selfish gene successor presumes (Newman and Müller 2000; Pigliucci 2001, 2010; West-Eberhard 2003; Gilbert and Epel 2009; Müller 2010).
Phenotypically plastic gene expressions are sufficiently recurrent across generations, and hence sufficiently heritable in a broad sense, to sustain adaptive behaviors that are only later, if at all, stabilized by genes. Genetic change goes not have to precede phenotypic change, including behavioral change. This phenomenon, which was postulated over a century ago and has since the 1950s been called the “Baldwin effect,” has been confirmed in the case of the differing abilities of human populations to digest milk as adults (West-Eberhard 2003; see Weber and Depew 2003). A similar idea is “niche constructionism,” which, inspired by Darwin’s little treatise showing how earthworms create their own (and incidentally our) species-specific environment, generalizes the Baldwin effect well beyond animals whose social way of life exhibits learned behavior and hence social inheritance (Lewontin 1983; Odling-Smee et al. 2003, Odling-Smee 2010; Pigliucci 2010).7
So much for Darwinism as reductionist genetics.
The Return of the Organism and Its Evolutionary Consequences
The way to integrate this range of emerging knowledge into evolutionary theory is to put the developmental dynamics of the organism back into evolutionary dynamics. Why “back”? Because they had been separated with the sea change that divided nineteenth from twentieth century Darwinism. To see why development and evolution were separated at that time requires us briefly to revisit a crucial episode in Darwinism’s history to which we only alluded in our earlier telling, and then only in a footnote. We are referring to August Weismann’s proof in the 1880s that characteristics acquired in the lifetime of an organism cannot be inherited. Weismann gave theoretical backing to empirical observation about this, thereby making the point all the more persuasively, by arguing that germ cells—egg and sperm—are “sequestered” (like a jury locked in a hotel room) from somatic cells too early in the ontogenetic or developmental process for them to be affected by the latter. It is only in the germ cells—what Dawkins later called “immortal replicators”—that variation, selection, and evolution occurs. Popular representations of Darwinism, which as we have said are still living more or less in the nineteenth century, may presume that individual organisms evolve, if only a little. Genetic Darwinism, as it mutated through the stages we have traced, became progressively more aware that from the perspective of population genetics this is a category mistake. Organisms develop. Only populations of organisms evolve, either by adaptation or, when gene flow between sub-populations ceases entirely, speciation (Hull 1978).
A great deal of knowledge was generated when the dynamics of gene- and trait-frequency change in populations were screened off from the process of development. Similarly, a great deal of knowledge was generated when geneticists conformed themselves to Crick’s transformation of “Weismann’s barrier” into the “Central Dogma of Molecular Biology,” namely, that information flows from DNA to RNA to protein and never the other way around (Crick 1970). It was by strict observance of this injunction that the genetic code showing how DNA is transcribed into RNA and then translated into protein, as well as how elementary mechanisms of gene regulation such as the lac operon mechanism work, were discovered. As Keller (2000a, b) predicted, however, the difficulty is that the knowledge gained in this way has falsified the anticipations by which it was acquired. To understand facts (1)–(9) and presumably many more to come, it is now widely acknowledged by evolutionary theorists, Darwinian and non-Darwinian—advocates of the evolutionary significance of stress-induced mutation and epigenetic inheritance are sometimes prone to dub themselves “Lamarckian,” for example, especially when reductionist versions of the theory of natural selection seem to monopolize the name “Darwinian” (Jablonka and Lamb 1995)—that Weismann’s barrier is quite permeable and that the process of evolution directly depends on that permeability. Weismann’s barrier is not a law of nature. It is a product of evolutionary history that applies more or less well to complex, multi-cellular forms of life whose development depends on nuanced coordination, but not to many kinds of single-celled or even simple multi-celled organisms. It is by stress-induced mutations that the latter find a way to adapt and, as lineages, to acquire an evolutionary future. It is by changes in gene regulation, often in response to environmental change, that metazoans do this (Colosimo et al. 2004; Gilbert and Epel 2009; Müller 2010). It is by the evolution of culture, and so by processes of trans-generational transmission of the sort that Lamarckism too generously ascribed to all of living nature, that human beings and their proximate ancestors and extinct cousins do it.
A natural way for evolutionary theorists to acknowledge these and other discoveries has been proposed by advocates of Developmental Systems Theory. They claim that genes are only one of many developmental resources that interact in the ontogenetic process (Oyama et al. 2001). In this light, genes themselves seem to have evolved to help stabilize the developmental process, DNA being more stable than its precursor and messenger, RNA. For this reason, it is misleading to say that genes “contain” coded, programed information. The “genetic program” conception of “gene action” has a variety of defects. It equivocates between genes as developmental resources and genes as units of inheritance in populations (Moss 2002). It assigns too much causality to genes in contexts of both development and population dynamics. Genes can’t do a thing without all other developmental resources. In this respect, Dawkins’s notion that genes are “self-replicators” approaches incoherence. He might say that he means only that genes are self-replicators when all other things are equal. But when all other things are actually made equal by spelling out in detail the developmental process by which genes express traits, any self-replicative privilege assigned to genes disappears completely (Moss 2002).
These insights have posed difficulties not only for selfish gene theorists, however, but for population-genetical Darwinians generally. In order to rebut the claim that mutation alone is the “creative factor” in evolution, population genetics as it was articulated in various ways between 1930 and 1970 set aside developmental considerations in order to exploit an analogy between gene frequencies in populations and energy distributions in statistical physics. In both cases, an equilibrium array of point-like entities is pictured as disturbed by impinging forces. It is sometimes said that population genetics treats organisms only as adults, since it focuses on the instant (comparable to a collision of atoms) at which a genetic contribution to the next generation is or is not made. But it doesn’t even do that. Organisms as developmental processes do not enter at all into the conceptual framework of population genetics as theoretical entities.
To be sure, this conclusion receives various interpretations depending on whether one’s version of the Modern Synthesis is organism- or gene-centered. Organocentric evolutionary theorists like Dobzhansky, Mayr, Stebbins, Simpson, Lewontin, and Ayala knew full well that the entities represented in and by population genetical models are and must be developmental systems.8 In spite of their differences, Gould, Pigliucci, and other advocates of “hierarchically expanded” or, alternatively, “developmentally extended” versions of the Modern Synthesis argue explicitly that it is only because the processes whose adventures are followed by Modern Synthesis have a developmental genesis that selection can occur at various levels of biological structuration (Gould 2002; Pigliucci and Kaplan 2007; Pigliucci and Müller 2010). The point of “expansions” and “extensions” of the Modern Synthesis is not to deny that population genetics depends on the fact that organisms develop. It is only to say that the subtle evolutionary processes that go on in and through the developmental process are not visible at the individual, but only at the population level. Doubtless this poses difficulties for how developmental genetics is to be integrated with the causal claims made by the Modern Synthesis (Walsh et al. 2002). But in taking these difficulties seriously, organocentric and multi-level genetic Darwinians show that they know that organisms are developmental and regard it as important.
For genocentric Darwinians, by contrast, the developmental nature of organisms is and forever will be completely irrelevant to evolutionary dynamics. Not only are Weismann’s barrier and the Central Dogma of Molecular Biology sacrosanct in this way of interpreting genetic Darwinism—apparent exceptions are treated as mere oddities—but the empirical adaptationism that is so marked a characteristic of genocentric theories depends on treating organisms not as developmental processes but as assemblies of independently adapted parts and traits. Accordingly, it makes considerable use of the analogy between organisms and artifacts, which have similar principles of assembly, and of “engineering” models of the ground of fitness. Hence arises the intense debate that has been repeatedly generated in this interpretive tradition about whether Paley’s God or Darwin’s natural selection is the designer of living beings (Dennett 1995; Dawkins 2006; for a history of the design inference and evolutionary theory, see Weber 2011).9 It is an issue that doesn’t even arise when the artifact analogy is denied or sidestepped, as it was by Dobzhansky, and is by evolutionary developmentalists (Dobzhansky et al. 1977, p. 4). Because development and design are not very congruent concepts, moreover, genocentric adaptationism also shows a marked tendency to reduce development itself to machine-like assembly—print out, as it were, from genetic blueprints—and to assert that the theory of natural selection in its most general, law-like formulation does not apply any more properly to organisms than to any other entities that exhibit variation, heritability, and selection—computer programs, for example (Dennett 1995, who calls the theory of natural selection “substrate neutral”). In this theoretical orientation, development is not merely ignored. It is deconstructed.
One thing is certain. It is difficult to represent developmental processes as population-level phenomena. This difficulty comes sharply into focus when we look at it from the perspective of the individual organisms in which ontogenetic changes that may or may not lead to evolution actually take place in the complex and highly responsive ways charted in the points (1)–(9). From this angle, the notion that the so-called “forces” of mutation, selection, genetic drift, and gene flow push genotypes away from their equilibrium distributions seems devoid of causal significance and even of any real meaning (Walsh et al. 2002). The actual causes of evolutionary change are single-generation developmental modifications whose effects are felt directly on the life cycles and reproductive success of particular organisms. Population thinking may be a good way to keep track of such changes as they spread or fail to spread, but it seems an empty gesture to say that anything causal happens at that level (or even anything explanatory except in a weak, merely explicative sense of “explain”). The notion of “forces” seems a particularly empty, and even deceptive, metaphor. Especially problematic as a “force” is the notion of genetic drift, an effect that is built into statistical representations of small populations but indicates no change at all in individuals—and even if it did could hardly count as a “force” since it happens purely by chance (Walsh et al. 2002).10 No wonder the role of development in producing and retaining variation through changes in the timing, place, and intensity of gene products was marginalized by population genetical Darwinism as a cause of evolutionary change. If it had not been, the basic representational devices on which population-genetic Darwinism of all stripes relies could not have arisen at all as offering explanations of evolution. No wonder, too, that the return of developmental variation as the proper cause of evolutionary change has stimulated consternation among defenders of the continued adequacy of the Modern Synthesis (Hoekstra and Coyne 2007).
Under these conditions, some theorists who support the “return of the organism” but who wish to remain Darwinian have re-accessed a view that, as we saw earlier, was popular in the decades between the rise of saltationist mutationism among early Mendelians and the population genetical revolutionaries. They defend the claim that the proper cause of evolutionary innovation is individual-level variation in genotypes and phenotypes in adaptive response to environments. Natural selection’s role is restricted to eliminating embryos and organisms that do not adapt (Gilbert and Epel 2009; but also see Laland et al. 2008). This idea is inconsistent with the leading claim of the Modern Synthesis that natural selection is a “creative factor” that over trans-generational time shapes very small, initially chance variations into adaptedness. The new position manages to evade the cutthroat Malthusianism that dogged early twentieth century “fly-swatter” selection precisely because it views organisms as flexible developmental agents. The presumptions are in their favor. They are not the vicious survivors of a war of all against all. The new version of eliminative selection can deny this because it recognizes that evolution’s main line has favored lineages that are inherently adaptive. Those that were too wedded to particular resources went extinct when environments changed. Nonetheless, we wonder whether the current revival of a filtering conception of natural selection and a corresponding denial of the creative role that the Modern Synthesis ascribed to it might prove as unstable and transient at the beginning of the twenty-first century as it did at the beginning of the twentieth.
Advocates of the view that evolution’s larger trajectory has put a premium on developmental systems that are adaptive because they are developmental and developmental because they are adaptive hark back to the main idea of the age-old epigenetic theory of organisms. Organisms, according to this theory, are irreducibly and inherently self-formative and self-organizing. At the very outset of our tradition, it seemed to Aristotle, in the course of arguing against Empedocles, that plants and animals are not assemblies of separate traits that arise by pure chance but just happen in some cases to be fit for their environments. Organisms come to be not as assemblies of parts but as integrated substances in which change at any stage of development is efficiently caused by the state of the embryo at the immediately preceding stage, the entire process repeating itself in acts of reproduction seen as the culmination of development itself (Depew 2008). The epigenetic ontology of organisms was revived at various times and in various ways by William Harvey, Caspar Friedrich Wolff, Johann Friedrich Blumenbach, and, through Blumenbach, the philosopher Immanuel Kant. Blumenbach and Kant explicitly appealed to self-organization, viewed not as self-assembly but as progressive self-differentiation, as the cause of self-formation (Grene and Depew 2004). Developmental Systems theorists as well as advocates of evolutionary developmentalism (EvoDevo) have more recently revived full-scale epigenesis by self-organization in reaction to preformationist tendencies that from the start were deeply embedded in molecular biology and genocentric adaptationism and remain there today (Newman and Müller 2000).11
Notions of organisms as autopoietic, self-formative, or self-organizing rely on models of self-organization in complex systems that have been emerging for several decades (Kauffman 1993). The point is not, as we are often misunderstood to be claiming, that self-organization causes adaptive self-development. Just as population genetical Darwinism made use of probabilistic-statistical models to track the dynamics of populations so that their causes (about which, as we have seen, there was considerable dispute) could be found, so we expect any “new synthesis” to capture the dynamics of complex systems so that their epigenetic way of emerging and evolving can be causally understood. Dynamical models tell you, at best, what can be expected and what is odd, what can be taken for granted, and what can be ignored. That populations will change gradually and continuously was an expectation built into the dynamic models that population genetical Darwinians used. Gould and Eldredge’s discovery of “punctuated equilibrium” seemed anomalous, even anti-Darwinian, against this background but not odd at all when mapped onto the “chaotic” dynamics of non-linear systems (Gould 2002, pp. 926–927). Similarly, in times dominated by Galilean–Cartesian–Newtonian physics, it seemed to advocates of epigenesis themselves, and not just to their adversaries, that this process is too teleological in a mystified sense to make for good mechanistic science. How could an as yet non-existent end point of development cause earlier states that somehow converge on this end without some sort of programing? This puzzle prevented Kant from thinking of biology as a genuine natural science; he endorsed epigenetic self-formation and self-organization as leading us to reflect on the fact that in our world there are beings that are signs and symbols of another, non-mechanistic one (Grene and Depew 2004). The great philosopher might have changed his mind on what our world is like, however, if he had known about feedback-driven cybernetic systems. He would be even more surprised by the recent articulation of mathematical models of self-organizing complex systems that assign to this world processes—modular structure, for example—that he could only project onto another.
Among those who think variation induced in the course of epigenetic self-organization is inherently adaptive, and hence is the “creative factor” in evolution, and who correspondingly restrict natural selection to filtering out the non-adapted, there exists a tendency to cite the role of the environment as causally primary both in inducing adapted variants and eliminating those that are not. Gilbert and Epel, for example, argue that many of the points we have summarized in the list of (1)–(9) imply that, in eliciting adapted variants ecological factors give new life to Darwin’s statement late in life that his greatest defect was in “not allowing sufficient weight to the direct action of the environment” (Darwin to Wagner 1879; Gilbert and Epel 2009, p. 370; see Müller 2010). It seems to us, however, that a thoroughly “ecological developmental biology”—the title of Gilbert and Epel’s fine book—will take full advantage of complex systems dynamics to portray organisms as less inner-driven in a quasi-Aristotelian teleological way. They will also paint natural selection in a less Spencerian, i.e., less externally forced and crudely eliminative, way than we sometimes encounter in post-Synthesis strains of thought (on Aristotle’s conception of organisms see Walsh 2006 and Ariew 2007; for niche construction, development, and evolution see Laland et al. 2008).12
This dichotomy can be transcended, we have long argued, only if organisms are conceived as nodes through which energy flows in ecological systems (Depew and Weber 1995). Organisms can be viewed in this light not simply when they are seen as intrinsically tied to the ecological systems of which they are crucial components, but when they are defined as ecological systems themselves—bounded and tightened ecosystems governed by massive feedback, both positive and negative, from and to the species-specific environments to which they are by definition related. This conception of organisms becomes possible when we understand that as developing and modularly structured systems organisms do not, as is commonly thought, defy the Second Law of Thermodynamics. On the contrary, as far-from-equilibrium dissipative structures, they build modular structure in the very act of paying their entropic debts (Prigogine 1962). It is because they are obeying thermodynamic imperatives that organisms self-organize, that is, increase in internal complexity without being guided or pushed by an outside force. Such systems, it should be observed, are inherently developmental. It is by cycling matter, energy, and information that they grow, differentiate, and, having reached the limit of their ability to buffer themselves against contingencies, fall apart.
On this view, organisms are, ontologically, processes rather than things or a fortiori artifactual things. If natural selection is a phenomenon that arises only in informed and bounded autocatalytic dissipative processes and plays a role in their evolutionary dynamics, it would seem that the units on which selection works are variations in feedback-driven cycling (Oyama et al. 2001; Weber and Depew 2001). Cycles at every level do in fact vary. By thinking of natural selection as discriminating among these variants, we are led beyond the current dichotomy between an eliminative view of selection and a causally reified conception of self-organization. The unresolved question is whether selection so conceived should be seen as the way organisms as a distinct sub-class of dissipative structures self-organize, or, perhaps, as working at every moment and every level of cycling—there are cycles within cycles in organisms and ecosystems—with self-organization, or as occurring only subsequent to the self-organizing genesis of organisms, when less efficiently autocatalytic organisms are selected against.13 This question raises another: Is the presumptive adaptedness of organisms that has been so prominent a theme in contemporary evolutionary developmentalism identical with or different from the necessarily trans-generational process that according to genetic Darwinism is required for adaptive natural selection? On the answer to this question depends whether adaptive natural selection is a genuinely creative process or is merely eliminative.
We confess to hoping that it is creative. We think that it can be so because even if evolution has increasingly resulted in processes whose tendency to vary is adaptively entrained to their environments, particular variations at any and all levels of cycling, from cell to ecosystem, are adaptively shaped only by being amplified in subsequent cycles (generations). Whatever the answer, however, we are confident that a new and more general theory of evolution is evolving that will explain the different strategies by which unicellular organisms and complex metazoa have acquired their various forms of “evolvability.” We are not much less certain that when this question has been answered the Modern Synthesis, along with the Weismann barrier and the Central Dogma, will have been shown to apply, suitably re-described, to part of the evolutionary continuum but not to the whole. We are sure, too, that when these facts have been articulated in a genuinely new and general theory, this theory (or family of theories) will have discovered far more about how life on earth originated in the first place than has any evolutionary theory thus far, especially Darwinian, and will have illuminated, too, how major forms of life evolved—something the Modern Synthesis never did—and how, among these forms, the emergence of culture as a plastic response to environmental contingencies took place (Weber and Depew 2001, 2003; Weber 2009, 2010).14
Scholars have searched in vain for thinkers who can be identified as actually asserting “Social Darwinism” as described in Hofstadter (1944) (Bannister 1970). This is the notion that success in an unconstrained free market economy proves an individual's biological fitness to survive in the struggle for existence together with the implication that constraints on free markets and charitable practices will result in the growing inability of a nation, race, or the whole species to preserve the fit. Failure to identify likely suspects who argued for this view does not imply, however, that social Darwinism is a negligible factor in the history of Darwinism. Social Darwinism is a discourse that circulated widely under the auspices of Progressive reformers, socialists of various stripes, and left liberal “fellow travelers,” all of whom followed Marx in thinking of Darwinism as Malthusianism projected onto all of living nature in order to legitimate laissez-faire economics. Marx protested that the supposed inability of working class people to restrain their appetites and to expand population beyond resources was nothing more than a slur. However that may be, Darwin was Malthusian to the core. For him the cause of the pressure that population increase puts on resources means that only some—the fit—can and will differentially survive. How Darwin applies this principle to humans is another question. He was no social Darwinian. But the issue is also moot. Among the advantages of twentieth century Darwinism is that fitness and unfitness are not defined by particular qualities, such as cunning aggression in the case of the supposedly fit or congenital degeneracy in the case of the unfit. (see Gayon 1998 for how the definition of fitness shifted.) Nor in twentieth century Darwinism does natural selection occur only at or near Malthusian limits. Unfortunately, however, these technical reformulations of the science of Darwinism are, after almost a century, still largely unknown in popular culture, which accordingly continues to circulate (and attack) nineteenth century images of a “social Darwinism” that no one ever held. Sometimes the complicity of Darwinians with racism, imperialism, or eugenics replaced “social Darwinism” as Hofstadter defined it in order to impute some sort of “social Darwinism” to actual Darwinians (Young 1985; Hawkins 1997; Crook 2007). But this strategy muddies the waters. It also draws attention away from the fact that Darwinism as it developed after 1937 has done everything it can to dissociate itself from its former ideological sins.
The term “neo-Darwinism” was first used to refer to Weismann’s rejection of the very possibility of the inheritance of acquired characteristics and his concomitant commitment (by presumed exclusion of a third alternative) to the “omnipotence of natural selection.” Darwin himself had been tolerant of both forms of inheritance. All twentieth century versions of Darwinism are neo-Darwinian in Weismann’s sense. But neo-Darwinism so construed includes the view that selection is a matter of eliminating the unfit as well as the quite different view of the Modern Synthesis that natural selection is a positive, even a creative, force that gradually shapes small genetic variations over trans-generational time into adaptive traits. Hence, to call the latter “neo-Darwinism” is to elide an important difference.
The popular science writing of Stephen Jay Gould was a major factor in reengaging the public in evolutionary discourse.
The mathematics of kin selection was worked out by W. Hamilton in the 1960s. The application of this formalism in the l970s to cooperation in ants by Wilson, the world’s greatest authority on these social insects, gave a huge boost to the prestige of kin selection theory and in turn to the selfish gene interpretation of it. Understandably, Wilson’s recent withdrawal of support for the kin selectionist interpretation of ants has been among the most eyebrow-arching events in recent evolutionary biology in view of the support it had earlier lent to selfish gene theory (Nowak et al. 2010.) It is worth noting, however, that Wilson had never been a selfish gene theorist. On the contrary, his training and inclinations were and are more oriented toward the “superorganism” concept.
Gould, no shrinking violet, responded by calling his opponents “Darwinian fundamentalists,” a term charged with negative connotations both religious and political.
See Kevles and Hood (1992), for an early collection of debates about the prospects of the HGP. The book contains absurdly unrealistic prophecies by W. Gilbert and J. Watson himself, who had become Director of the HGP at the National Institutes of Health, as well as an early formulation of Keller’s skepticism.
References in the list of points (1)–(9) (as throughout this paper) are representative, not (by a considerable margin) exhaustive.
This fact can be seen perspicuously by considering the relationship between Dobzhansky and the developmental biologist Waddington. Waddington claimed that no evolutionary synthesis worthy of the name would be complete until it came back to the fundamental problem of development (Gilbert 1994, 1998). Dobzhansky did not disagree. He merely thought, probably wrongly, that the developmental genetics of the future would be subsumed under population genetics. Like Waddington, Dobzhansky also thought highly of another pioneering developmental geneticist, I. Schmalhausen. By using Schmalhausen’s ideas about development to express his and Waddington’s belief that natural selection is not only directional, but has evolved mechanisms for stabilizing normal development, Dobzhansky was in effect saying that natural selection applies uniquely to organisms considered as developmental systems. See Dobzhansky (1970), Gilbert (1994, 1998), and Depew (2010b). Most of the tension between the Modern Synthesis and developmental biology has been based on Mayr’s attack on another pioneering developmental geneticist, Goldschmidt. Gould, in his introduction to a reissue of Goldschmidt (1940), calls this judgment into question.
On the religious background of the adaptationist Oxford School of interpreting Darwinism, whose recent adepts have taken a decidedly atheistic turn, see England (2001).
The philosophers who urge the anti-causalist interpretation of statistics and probability in genetical Darwinism take at face value the claim of Dawkins and others that genocentrism is the most fully articulated version of genetical Darwinism. They are reacting to the overly causalist conception of what genes do in Dawkins interpretation. Still, they do impose a burden of proof on non-genocentric versions of the Modern Synthesis, even if it is a burden that can be met. We interpret Pigliucci and Kaplan (2007) and Pigliucci and Müller (2010) as meeting the burden.
We are distinguishing “full-scale” epigenesis from the more limited meaning of “epigenetic” that took hold after Weismann and is now common: everything that happens to an organism after the sequestration of germ cells. This meaning of “epigenetic” has more recently given rise to a third. The discovery that not only gene sequences but chemical markings of DNA (methylation) are heritable has led to the emergence of “epigenetics” considered as the study of these modifications. The third meaning presumes that Weismann’s sequestered germ cells are Dawkins’s “immortal replicators,” that is, coding sectors of DNA. Since methylation seems to defy the dogma that only DNA is heritable, it has been semantically assimilated to epigenesis in the second sense. Correctly understood, methylation and other strictly heritable, but non-DNA, developmental recourses should lead to restoration of the first, ancient, “full-scale” sense of epigenesis.
We have written on the possible ways in which self-organization can be related to natural selection (Depew and Weber 1995). Our list has been commented on, sometimes critically, by Richardson (2001), Swenson (2010), and Linde Medina (2010). We appreciate these responses. In particular, we appreciate Swenson’s point that claiming that natural selection is just self-organization in certain kinds of systems need not imply elimination or reduction of natural selection to something else (Swenson 2010). We have no dogmatic view to defend on this point. It seems clear enough to us that the issue will be decided by the progress of science itself, which includes discussion of conceptual issues.
This article is an English version of DARWINISMO: Il destino dell’evoluzione dopo la Sintesi Moderna; in Frontiere della biologia: Prospettive filosofiche sulle scienze della vita (Davis J, Michelini F, eds); Milan-Udine: Mimesis, in press. It appears with the permission of the editors.