An honest appraisal of evo devo

In a review of a new book edited by Alan Love, The evolution of “evo-devo”, Adam Wilkins makes a few telling criticisms of the sub-field I enjoy.

Evo-devo has come a long way since 1981 though the Dahlem Conference laid some of the important groundwork for what followed and was, indeed, widely appreciated as having done so. Yet, troublingly, the field remains, for many evolutionary biologists, something of a side-show, a “boutique” subject within evolutionary biology as a whole. Several of us, in the 1990s, warned that this might happen. This is in contrast to some of the early expectations, which involved positing a coming central role for this discipline within evolutionary biology as a whole. A few of the contributors evidently feel that it has achieved such a position but I think that a broad survey within biology would reveal that not to be the case. If it failed to develop its full potential, why? Opinions will vary but my own hunch is that one factor is that the field has largely avoided incorporating much of the rich material that developmental genetics offers for understanding developmental and morphological change. The one general concession to such genetics, noted in passing in one of the chapters, is the insistence that most developmental change in evolution involves alterations in cis-regulatory elements for regulatory genes. There is, of course, good evidence for this but it is not the whole story and ignores both other mechanisms and the possible dynamics of the incorporation of such change in populations. That last thought, however, introduces what is, in my view, the second weakness of the field: evo-devo remains largely a zone devoid of population thinking. The great strength of classical evolutionary biology was that it focused on the nature of transformation of populations over time – both genetically and phenotypically – and provided a crude general mechanism for understanding such transformations. Its corresponding failing was that it largely ignored the details of the source materials for such change. Evo-devo's main strength and weakness are just the reverse. These reciprocal differences in emphasis amount to perceptual and intellectual differences about what is important in considering evolutionary change. Such differences in attitude continue to create a divide between evo-devo and classical evolutionary biology. This volume does not address this issue at all and I think that is a regrettable omission.

I've highlighted the two key points, although I think they're both rooted in the same problem. 1) I think there is a superficial focus on developmental genetics, but what we're missing is the experimental perspective. 2) True enough that there is a lack of population studies (I can think of the stickleback work on recent evolution of small populations as a counter-example), but there the problem is that if you're focusing on the great grand questions of evolution, like where the notochord came from, you're simply not going to find much variation within extant groups. All fish have notochords. All zebrafish populations have notochords. You're just not going to have any material to work with if you try to study how the expression of notochords vary in a population that is over half a billion years removed from an ancestral population that did have interesting differences in a nascent structure.

The key problem is that the field has long been interested in morphological and molecular differences at the phylum and class level. What we need to do is ask better questions that are appropriate on a smaller scale, and are more amenable to experiment and genetic analysis. Narrow the scope, more work on differences in fruit fly wings and in the circuitry of tissue specification in closely related species of echinoderms, for instance.

Of course, the appeal of evo-devo is often in those gigantic huge intractable questions that involve comparing fruit flies and echinoderms. Evo-devo without the grandiosity is harder to market.

Wilkins AS (2015) The evolution of “evo-devo”. BioEssays 37(12):1258–1260.