Biologos has posted the next segment of its comprehensive response to Darwin's Doubt (hereafter, DD). Disappointingly, these entries - comprising parts 1and 2 of philosopher of science Robert Bishop's 4-part critique - do not reply to the scientific arguments or evidence presented in DD. Instead, Bishop focuses on what he calls the "rhetorical strategy" of DD, and its framing of the current status of evolutionary theory. Bishop finds fault both with the rhetoric and the framing of DD, but, as I'll explain below, he does so by mischaracterizing DD's presentation of evolution. Moreover, Bishop's critique contains serious errors in its discussion and understanding of evolutionary theory, which vitiate his case against DD. Thus, the book still awaits a response that meets its central arguments head-on.
Does DD Employ a 'Divide-and-Conquer' Strategy - or Just Tell It Like It Is?
In Darwin's Doubt, Meyer argues that intelligent design best explains the origin of the biological information necessary to build the animals that appeared abruptly in the Cambrian period. In support of this argument, Meyer demonstrates that neither textbook neo-Darwinism, nor more recent versions of evolutionary theory, provide an adequate explanation for the explosion of novel biological form and information (both genetic and epigenetic) that arose in the Cambrian period.
In chapters 8-14, the book makes several separate evidentially-based arguments to demonstrate the inadequacy of the neo-Darwinian natural selection/random mutation mechanism as an explanation for the origin of animal life. But in chapters 15 and 16, he also explores the ideas of a wide range of evolutionary biologists who have expressed dissatisfaction with current neo-Darwinian theory and formulated alternative evolutionary models. Meyer then critiques these alternative proposals as well, showing in each case that they either fail to address the problem of the origin of the necessary biological information or that they simply presuppose earlier unexplained sources of such information.
Bishop finds this approach "misleading," because - he argues - the alternatives that Meyer addresses are not genuinely replacements for current neo-Darwinian theory, but are merely additions orexpansions to a basically sound core. He calls DD's analysis a "divide-and-conquer" strategy:
Meyer rightly points out that there has been a long history of trying to understand the details of macroevolutionary change in neo-Darwinian evolution...Meyer successively reviews a variety of attempts, such as evo-devo [evolutionary developmental biology] to rectify this shortcoming in macroevolution. Each attempt surveyed is presented to the reader as being in competition with and a replacement for neo-Darwinian evolution (population genetics and natural selection)....[but] researchers working in evo-devo typically don't see themselves as replacing population genetics and natural selection.
Well, evo-devo researchers and many others are seeking to replace something that they perceive as wrong with textbook theory. More often than not, that something is one, or indeed more than one, of neo-Darwinism's key pillars (DD, pp. 292-3): (1) small-scale, randomly-arising variations and mutations as the raw materials of evolution, (2) natural selection as the primary creative process, and (3) heritability grounded in the vertical transmission of DNA.
Contrary to Bishop's critique, DD is quite careful to spell out in each case exactly which pillar is under attack by evolutionary theorists seeking alternatives, and why the proposed alternatives themselves are nonetheless unable to explain the Cambrian Explosion. And DD correctly points out (again, contra Bishop) that the proposed alternatives and textbook theory are mutually contradictory. The new proposals cannot be seamlessly grafted onto a core of existing theory, because the investigators in question see existing theory as gravely defective, not basically sound. To interpret the situation otherwise would be at best naïve.
Let's consider some examples. Geneticist Michael Lynch of Indiana University, whose alternative evolutionary proposals are discussed extensively in chapter 16 of DD, has argued that "nothing in biology makes sense except in the light of population genetics" (Lynch 2007b, p. 8597). At first blush, this statement appears to support Bishop's claim that proposed alternatives build on, but do not replace, existing theory. After all, population genetics and natural selection go hand-in-hand, right?
But watch what Lynch does with his dictum about population genetics. He uses it as a battering ram to smash right through the doors of textbook (i.e., received) theory. Starting from the non-negotiable principles of population genetics, Lynch asserts, one must acknowledge that non-adaptive causes such as random genetic drift
dictate what natural selection can and cannot do. Although this basic principle has been known for some time, it is quite remarkable that most biologists continue to interpret nearly every aspect of biodiversity as an outcome of adaptive processes. This blind acceptance of natural selection as the only force relevant to evolution has led to a lot of sloppy thinking, and is probably the main reason why evolution is viewed as a soft science by much of society. (2007a, p. xiii)
All right - so what do the textbooks say? What is the core neo-Darwinian theory, which Bishop claims is basically sound?
We can consult Dobzhansky, Ayala, Stebbins, and Valentine, a standard and widely-used text (1977, p. 504): "According to the theory of evolution...natural selection is the process responsible for the adaptations of organisms, and also the main process by which evolutionary change comes about." Or consider George Williams's classic, influential analysis of natural selection: the process, he argues, provides "the only acceptable theory of the genesis of adaptation" (1966, p. 251). Or Dawkins (1982, p. 19): "Adaptation cannot be produced by random drift, or by any other realistic evolutionary force that we know of save natural selection."
Looks like a fundamental theoretical conflict, doesn't it? In direct opposition to received theory, Lynch wants to dump natural selection from its central explanatory role, and isn't coy (2007a, p. 369) about his reasoning or motivation: "[I]t is a leap to assume that selection accounts for all evolutionary change, particularly at the molecular and cellular levels. The blind worship of natural selection is not evolutionary biology. It is arguably not even science."
"Not even science" is hardly the sort of language one expects from a biologist mildly or moderately discontent with current theory, looking to graft his additional considerations into a more or less healthy core theory. The same is the case with other biologists seeking alternatives, whom Bishop wants to tuck into the neo-Darwinian fold.
Consider for instance Cal Tech developmental biologist Eric Davidson, whom Bishop says (in the online supplement to his review) is "working out a synthesis of evolutionary development and neo-Darwinian evolution." Really?
In the opening of a 2011 paper that Bishop himself cites, Davidson (pp. 35-6) gives his candid assessment of neo-Darwinian theory:
...it gives rise to lethal errors in respect to evolutionary process. Neo-Darwinian evolution is uniformitarian in that it assumes that all process works the same way, so that evolution of enzymes or flower colors can be used as current proxies for study of evolution of the body plan. It erroneously assumes that change in protein coding sequence is the basic cause of change in developmental program; and it erroneously assumes that evolutionary change in body plan morphology occurs by a continuous process. All of these assumptions are basically counterfactual. This cannot be surprising, since the neo-Darwinian synthesis from which these ideas stem was a pre-molecular biology concoction focused on population genetics and adaptation natural history, neither of which have any direct mechanistic import for the genomic regulatory systems that drive embryonic development of the body plan.
The emphases are mine, but they're probably unnecessary - it is difficult to miss Davidson's thrust. As far as the origin of animal body plans is concerned, neo-Darwinism isn't incomplete or insufficient. It is dead wrong. And no biologist in his good senses would seek to synthesize his ideas with a corpse.
We could go on in this vein for pages, but the point is clear. When a scientist says that something is wrong with a current theory, we need to pay attention to the details of his objection. Is he troubled by some minor matter, or speaking about the core of the theory? The alternative evolutionary proposals presented and critiqued in DD reject core propositions of neo-Darwinian theory, not peripheral theoretical commitments. Thus, Stephen Meyer is not dividing and conquering, but simply reporting; it's up to the reader to decide if he wants to stay with neo-Darwinism, or try his luck elsewhere.
Does DD Shift the Questions Arising in Evolutionary Theory?
Bishop's second critique of DD turns on what he calls the book's "question-shift strategy." As he puts it,
This strategy involves equivocating on the notion of origin. In the biology and paleontology literature, when scientists discuss the origin of Cambrian body plans, they mean the modification and diversification of body plans from preexisting body plans.
The statement in italics (Bishop's own emphasis) is simply false. I want to add inexplicably false, because - with a moment's reflection - one realizes that even a "preexisting" body plan must be a body plan for some kind of animal, and must have arisen at some discrete interval in Earth history. Consider: one billion years ago, no animals; 500 million years ago, lots of animals, of many different types.
No matter how one carves up the puzzle, one cannot bracket the problem of primary origins indefinitely. In other words, the problem of the Cambrian Explosion by definition includes the origin of the first animals, meaning the first body plans (whether those plans diversified later or not). Given any evolutionary approach to the data, there is no way around answering the question, "How did the first animals come to be?"
Bishop makes this serious error more inexplicable by conflating the problem of the origin of animal body plans with the problem of the origin of life, and Darwin's treatment of that problem in theOrigin of Species:
[Modification and diversification] is the customary usage in the literature since Darwin's publication...where he makes clear that he is seeking only to explain speciation, not how the first species arose. The latter question is the origin of life issue, a separate question from how an ancestor species may be connected with descendant species through descent with modification.
But the origin of metazoan multicellularity and the diverse macroscopic architectures of the Cambrian Explosion are chapters in the evolutionary narrative hundreds of pages later than the origin of life itself. Indeed, the origin of life and the origin of animals constitute discrete events in the history of life separated by billions of years of Earth history. Along the way, we must pass through such earlier, but absolutely necessary, chapters like the division of the three primary domains (Bacteria, Archaea, Eukarya), the origin of cell organelles, the origin of eukaryotic cytoskeletal complexity, the origin of colonial protists, the origin of sexual reproduction, cellular differentiation, and developmental pathways, and so forth - that is, through a whole lot of complexity-building and evolutionary origins events. Throughout the narrative leading to animal body plans, tens of thousands of novel biological traits must come to be where they did not exist before - namely, they must originate.
That is the "customary usage" since Darwin, unless one tries to offload the hard problems by simply naming them "origins" questions and stipulating that evolutionary theory does not address them. But then what? If the theory of evolution is anything, it is an attempt to explain how x came to be - i.e., originated - where x did not exist before. That includes the first animal (metazoan).
This problem has nothing whatsoever to do with the origin of life, or only the most tenuous connection. Indeed, two different branches of evolutionary theory--chemical and biological evolutionary theory--address these two separate questions. For all that, one might assume (as Darwin seemed to intimate from time to time) that the first cell was divinely created, and the puzzle of animal origins would still remain. Thus, when Bishop writes that "the logical fallacy...is Meyer's falling into equivocation on two different senses of 'origin' and shifting all diversification questions to origin of life questions," he is just flatly mistaken.
Still Awaiting Engagement
Thus, at the end of the day, it really doesn't matter whether the contemporary evolutionary theorists that Meyer discusses in Darwin's Doubt are attempting to supplement neo-Darwinian theory, replace it with something fundamentally new, or replace some, but not all, parts of the theory. What matters is whether any of these theories can explain what needs to be explained: the origin of novel animal body plans and the biological information necessary to produce them. InDarwin's Doubt, Meyer argues that neither neo-Darwinism, nor recently proposed alternative theories of evolution (punctuated equilibrium, self-organization, Lynch's neutral theory, neo-Lamarckian epigenetic inheritance, evolutionary developmental biology and natural genetic engineering) have solved this problem. And certainly Bishop himself offers no solution to it. Indeed, by focusing his analysis on the alleged rhetorical strategy of DD rather than its scientific case, Bishop fails to address the central arguments of the book--a failed rhetorical strategy if ever there was one.
There are an infinite number of roads one can take to avoid a challenge. To date, the Biologosreviewers (first Ralph Stearley, now Robert Bishop) have taken some of those roads, veering away from, or around, the central arguments and lines of evidence laid out in Darwin's Doubt. Thus, the book's fundamental challenge to current evolutionary theory remains unanswered.
References
Davidson, Eric. 2011. Evolutionary bioscience as regulatory systems biology. Developmental Biology357:35-40.
Dawkins, Richard. 1982. The Extended Phenotype. San Francisco: W.H. Freeman.
Dobzhansky, T., F. Ayala, G. Stebbins, and J. Valentine. 1977. Evolution. San Francisco: W.H. Freeman.
Lynch, Michael. 2007a. The Origins of Genome Architecture. Sunderland, MA: Sinauer Associates.
Lynch, Michael. 2007b. The frailty of adaptive hypotheses for the origins of organismal complexity. PNAS 104:8597-8604.
Williams, George. 1966. Adaptation and Natural Selection. Princeton: Princeton University Press.
