As the next installment of our Reviewing Darwin’s Doubt series, we present part two of Robert Bishop’s four-part review of the book.
In the previous post, I discussed the exciting, emerging synthesis that is developing among neo-Darwinian evolution, developmental biology and epigenetics. The development of evolutionary theory in recent decades is fascinating and offers new ways to think about God’s action in the world that I’ll touch on toward the end of this series. In this post, I want to discuss the main rhetorical strategies in Darwin’s Doubt.
Last time, we saw examples of how Intelligent Design (ID) advocate Stephen Meyer paints a picture in Darwin’s Doubt of the evolutionary literature as offering competing explanations for how evolution operates. One feature of his narrative is the claim that evolutionary development (evo-devo) raises profound difficulties for neo-Darwinian evolution. This way of framing the literature serves Meyer well rhetorically for his case advocating ID, and neo-Darwinian evolution alone does look inadequate to explain macroevolutionary change. However, his framing doesn’t make good sense of either the evolutionary or developmental biology literatures, or the paradigm shift that has been taking place within evolutionary biology the last three decades.
For example, the evo-devo authors Meyer cites view genetic variation and natural selection as being incorporated within evo-devo, not as outside and opposed to it. A popular audience reading Darwin’s Doubt will not be able to distinguish rhetorically createdproblems for evolution from the actual discussions in the biology literature.
The divide-and-conquer strategy works like this: First, Meyer rightly points out that there has been a long history of trying to understand the details of macroevolutionary change in neo-Darwinian evolution. Gilbert et al. (1996) gives a brief, but helpful account of this in the 20th century. Second, Meyer successively reviews a variety of attempts, such as evo-devo, to rectify this shortcoming in macroevolution (chs. 8-16). Each attempt surveyed is presented to the reader as being in competition with and a replacement for neo-Darwinian evolution (i.e., population genetics and natural selection). Third, Meyer assesses the “alternative” to the neo-Darwinian account and finds it lacking as a viable alternative for explaining the diversification of Cambrian body plans. Intelligent Design is left standing as the best possible explanation of the Cambrian explosion.
The divide-and-conquer strategy in Darwin’s Doubt, however, offers a misleading picture for the reader. As I pointed out last time, researchers working in evo-devo typically don’t see themselves as replacing population genetics and natural selection. More generally, biologists, as illustrated by Gilbert et al., seek synthesis as the more fruitful approach to understanding descent with modification, where genetic variation and natural selection work along with other processes. Genetic variation and natural selection are seen as inadequate for descent with modification in the absence of these other processes. As Gilbert et al. put it, “macroevolutionary processes could not be explained solely by microevolutionary events” (p. 362, emphasis added). Microevolutionary processes are seen as contributing some of the necessary conditions for macroevolution, but, as has been widely recognized at least since the 1970s, are not sufficient conditions for macroevolution.
For detailed examples of how Meyer assesses evo-devo and the development of gene regulatory networks (GRNs) as independently inadequate to account for the macroevolution of new body plans in the Cambrian,see these supplementary materials. Neither the division nor the conquest parts of Meyer’s strategy work with respect to evo-devo or GRNs. These examples are representative of how the divide-and-conquer strategy functions for the other “alternatives” to classic neo-Darwinian evolution Meyer considers (e.g., epigenetics).
The Question-Shift Strategy
The second strategy playing a crucial role in Meyer’s case for ID is what I call the question-shift strategy. This strategy involves equivocating on the notion of origin. In the biology and palenotology literature, when scientists discuss the origin of Cambrian body plans, they mean the modification and diversification of body plans from preexisting body plans. This is the customary usage in the literature since Darwin’s publication of On the Origin of Species, 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 though descent with modification. Meyer’s question-shift strategy is to shift from diversification of existing body plans to the origin of the first body plan. Yet, the question of how the first body plan arose isn’t what the biology and paleontology literature on the Cambrian is addressing.
A representative example of this question-shift strategy appears in Meyer’s discussion of whether changes in genes and genetic information might lead to new body plans. He critiques these accounts because they assume “the existence of significant amounts of preexisting genetic information...and then suggest various mechanisms that might have slightly altered or fused these genes together into larger composites. At best, these scenarios ‘trace’ the history of preexisting genes, rather than explain the origin of the original genes themselves” (p. 212, emphasis in the original).
Meyer and I would agree that the literature he surveys doesn’t answer origins of life questions. But note that he shifts the question from accounts of how existing genes may evolve to accounts of the origin of the first gene. He then faults this literature for not addressing the origins of the first genes. This equivocation on “origin” allows Meyer to critique studies of how genes diversify as inadequate to explain the advent of the first genes. Indeed, in a subsection titled “Begging Questions” Meyer accuses researchers in the literature of begging the question of the advent of the first genes by only considering mechanisms that could lead to modifications of preexisting genes (pp. 215-219). But it is Meyer who shifted the question from the one the literature addresses–the evolution of genes–to the advent of genes.
As a second example, consider Meyer’s claim that Erwin and Davidson (2009),
rule out both observed microevolutionary processes and postulated macroevolutionary mechanisms (such as punctuated equilibrium and species selection) as explanations for the origin of the key features of the Cambrian explosion. They insist that the requirements for constructing animal body plans de novo ‘cannot be accommodated by microevolutionary [or] macroevolutionary theory.’ (Meyer, pp. 355-356)
While Erwin and Davidson’s paper focuses on how preexisting gene regulatory networks might be diversified over time, Meyer’s use of “de novo,” here, in the absence of further qualification, shifts the average reader’s frame of reference from diversification of GRNs to the advent of the first GRN. Now, Erwin and Davidson do make reference to de novo generation of GRN sub-circuits, but what they mean is the redeployment of existingGRN circuits as a means of diversification (e.g., 2009, p. 145) rather than Meyer’s sense of de novo (first advent of a GRN; see supplementary materials).
These examples merely scratch the surface of the question-shift strategy in Darwin’s Doubt (three more examples are given in the supplementary material). Unfortunately, in each instance of the question-shift strategy, Meyer leaves his readers with the impression that the biology literature commits the fallacy of begging the question: of assuming an explanation for the advent of the first genes, GRNs, and body plans while only discussing the diversification of preexisting genes, GRNs, and body plans. Meyer is correct that the diversification mechanisms he surveys are inadequate for explaining advent of the first gene, GRN, or body plan.
Nevertheless, there is no question-begging going on in the literature, itself, because it’s addressing diversification questions. These are the Cambrian questions! The logical fallacy, here, is Meyer’s falling into equivocation on two different senses of “origin” and shifting all diversification questions to origin of life questions. Perhaps Meyer falls into the equivocation because of his fixation on the enormously challenging problem of origin of life. Nevertheless, it’s no fault of the biology and paleontology literature for failing to address Meyer’s first advent question. That’s the task of origin of life research and the subject of his book Signature in the Cell (reviewed on this blog here by Darrel Falk, Meyer’s response here, and Falk’s rejoinder here).
In the next post, I’ll examine Meyer’s inference to ID as the best explanation of Cambrian body plans and how what I’m calling the “divide-and-conquer” and “question-shift” strategies shape that inference. As the series continues, we’ll see that one doesn’t have to choose between God and evolutionary theory as explanations for the incredible variety of life on Earth.
- Some such as Jerry Coyne and Richard Dawkins may dismiss the relevance of evo-devo, but they are being left behind in the wake of the developing synthesis. [return to body text]
- Scott F. Gilbert, John M. Opitz, and Rudolf A. Raff, “Resynthesizing Evolutionary and Developmental Biology,”Developmental Biology 173 (1996): 357-372. [return to body text]
- Eric H. Davidson, The Regulatory Genome: Gene Regulatory Networks in Development and Evolution. New York: Academic Press (2006). [return to body text]
- Douglas Erwin and Eric Davidson, “The Evolution of Hierarchical Gene Regulatory Networks,” Nature Reviews Genomics 10(2009):141-148. [return to body text]
- Erwin and Davidson do argue that “Neither microevolution nor macroevolution takes into consideration the impact of past changes in developmental GRNs on the future course of evolution” (2009, p. 146). Yet, they also argue that GRN circuits are subject to selection. So while population genetics and selection are insufficient to explain the diversification of GRNs, contrary to the impression left by Meyer’s divide-and-conquer strategy, Erwin and Davidson are not repudiating neo-Darwinian theory simpliciter. Instead, consistent with what we saw previously for Gilbert et al. (1996), they are pursuing a synthesis of developmental and evolutionary biology.[return to body text]
- Meyer often puts his arguments in terms of information, but this makes no difference to the question-shift strategy. The issue of how pre-existing information grows and diversifies is distinct from how information originates. [return to body text]