Let’s finish up with some excerpts from Adam Wikins’s paper, “Between ‘‘design’’ and ‘‘bricolage’’: Genetic networks, levels of selection, and adaptive evolution” (PNAS 2007 vol. 104, pp. 8591-8596). We have seen two levels of constraint on the “choice” of evolutionary trajectories: 1) the set of preexisting properties of the recruited molecule and 2) the recruited gene must be expressed in the appropriate context. Wilkins next points out that such cooption often rises above the level of the gene and involves modules:
Hence, the tinkering/borrowing process at the molecular level is somewhat more channeled, hence restricted, than the metaphor of bricolage might suggest. In addition, however, it has become equally clear over the past decade that the recruitment process is often not a gene at a time but a functional grouping of genes, a network ‘‘module’’ (reviewed in ref. 31). This is most obviously relevant in the cases where a preexisting signal transduction pathway becomes recruited, via an enabling mutation, to a new use.
Wilkins then spends a good bit of time exploring network modules and their significance, leading up to this rather striking claim:
A network perspective, however, has further value for evolutionary biology. A detailed knowledge of genetic networks, which necessarily includes an understanding of their component modules, can provide even more: such knowledge provides a platform from which to assess the relative a priori probabilities of certain evolutionary trajectories. Such assessment would necessarily be approximate, but even that degree of understanding would be sufficient to allow the beginnings of a predictive approach to evolutionary trajectories, extending the potential range of hypothesis testing in evolutionary biology. It will be remembered that it was the apparent dearth of falsifiable hypotheses in evolution that led K. Popper initially to question whether evolutionary biology was truly science or simply a ‘‘metaphysical’’ framework of thought (48), although he later modified his stance (49).
Yes, a telic perspective, especially one that includes front-loading, might indeed give evolutionary biology a level of predictive precision that it currently lacks. After all, recall that Michael Lynch noted “Because it deals with observations on historical outcomes, frequently in the face of incomplete information, the field of evolution attracts significantly more speculation than the average area of science.”
This possibility, of predicting phenotypic outcomes from mutations in well characterized pathways, is, of course, only a potential for future work. At present, there is insufficient knowledge of any network, and of few network modules, to allow this kind of analysis. Furthermore, knowing the probability of a developmental outcome is only the beginning of estimating the chances of a particular evolutionary trajectory, which will be influenced at many steps by selective opportunities, genetic drift, the occurrence of rare external disasters (e.g., mass extinctions), or other chance events.
This speaks to a criticism/suggestion I recently received. But notice what Wilkins says next:
Yet, knowing which phenotypic outcomes are more likely than others would provide a first step toward assessing the likelihood of certain trajectories vs. others. That there are certain propensities toward certain evolutionary trajectories is shown by the numerous instances of parallel evolution in related lineages that evolutionists have found. Although the traditional emphasis to explain this phenomenon is similarity of selective pressures, there must also be some inherent biases built into the genetics and development of the branching lineages that display it (52). (emphasis added)
So as you can see, my focus on convergent and parallel evolution have been precisely the type of analysis that Wilkins uses to support the idea that evolution is more predictable that we would assume using the bricolage metaphor. On target, bunny boy.
Question to ponder – If Wilkins’s view of evolution is validated by science, wouldn’t this mean that my front-loading hypothesis would then be strongly supported?