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1 May 2008 From Embryology to Evo-Devo: A History of Developmental Evolution
Jessica A. Bolker
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From Embryology to Evo-Devo originated in a 2001 Dibner Institute workshop organized by the book's editors. Manfred D. Laubichler is an assistant professor of biology and an affiliated assistant professor of philosophy at Arizona State University; Jane Maienschein is Regents' Professor and Parents Association Professor at the same university, where she also directs the Center for Biology and Society. Both are long-time observers of, as well as participants in, the modern emergence of evolutionary developmental biology, or “evo-devo.” As they note in the introduction, we continue to confront “a rather old cluster of scientific problems of embryos, development and evolution,” and struggle with how to think about them and what to do about them in the lab. The quest to articulate how ontogeny and phylogeny fit together, and to achieve some kind of conceptual continuity that unifies their disparate timescales and explanatory modes, is a long-standing one. This volume, an anthology of essays, combines a history of these efforts with attempts to move the project forward.

The book presents workshop participants' attempts to record the history of evo-devo—or a series of interrelated histories—and also tries to make the case that this history is important to the field's present and future. The first objective is certainly achieved: the collection offers a multifaceted construction of the history of evo-devo. The second task meets with less success, however: by the end of the book, it is not clear exactly how or why evo-devo's history matters to its current practice or practitioners. The volume will certainly be of interest to historians, both for its immediate content and for the variety of historiographic approaches it comprises. Although it will not engage all evo-devo biologists, it will appeal to those interested in the origins of their discipline.

There are many different ways to construct history, whether of evo-devo or anything else: one can focus on individuals, institutions, or central questions. Each of these approaches is represented in this anthology. The first step, of course, is to decide what one is constructing a history of—in this case, the biological discipline (or subdiscipline, or interdiscipline) of evolutionary developmental biology. Evo-devo is variously construed as an overlap between two otherwise independent fields, a set of questions, or an attempt to fill “explanatory gaps” in or between evolutionary and developmental biology. Although Brian K. Hall cautions that “the title [of the book] is, obviously, not meant to be taken literally,” some contributors do in fact view evo-devo as the lineal successor of comparative (evolutionary) embryology. One topic of discussion is whether, or to what extent, “modern” evo-devo is finally getting somewhere with the classical questions of comparative embryology—as well as precisely which of those questions were the central ones in the first place. (Amundson [2007] focuses on this issue in his review of the book, contrasting it with the 1980 volume The Evolutionary Synthesis, edited by Mayr and Provine.)

Evo-devo has achieved substantial mainstream success and recognition, including all the essential paraphernalia of an established discipline (dedicated journals, National Science Foundation funding, etc.). Now that the discipline is mature, we have to guard against stodginess; one way to do that may be to resist defining the field too carefully or insisting on a single version of its history.

Two things about this historical project are particularly interesting. The first is the timescale: this is very recent history (the 2001 workshop focused on the interval between the 1920s and the 1970s), and writing the history of a field at so short a temporal remove raises some important questions—for instance, how well can we judge in the present the likely future significance of particular questions, institutions, or individuals? As is clear by the end of the volume, we do not even necessarily agree on their past significance.

Second, scientists were engaged in the historiographic project alongside historians of science. One unusual aspect of modern evo-devo is that a number of the key scientific players are also seriously interested in, and knowledgeable about, the history of their field (although it is not clear that this interest materially affects the direction of their biological research programs). Günter P. Wagner reports that a colleague compared his attending a workshop about the history of his own field with being a “bird…at a meeting of ornithologists” (p. 525). Nevertheless, the participation of scientists in addition to that of historians clearly brought much to the project.

But what do the birds get out of it? That is, what can this volume offer to other scientists in or entering evo-devo—especially those who might not be historians on the side? One answer is an appreciation of history within a field. For example, history may be particularly useful in explaining why certain people and ideas become very influential while others remain on the sidelines, as well as why some individuals are honored as intellectual progenitors of the modern discipline while others are deemed irrelevant (or worse). Marsha L. Richmond, Stuart A. Newman, William C. Wimsatt, Alan C. Love, and others discuss the roles played by the likes of Richard B. Goldschmidt, Patrick Bateson, Rupert Riedl, and D. Dwight Davis. In the most detailed example, James Griesemer describes how geneticists have retrospectively claimed the contributions of Gregor Mendel—though read another way, those contributions could equally well be considered “developmental,” and Mendel himself did not make the distinction at all.

A second important message for scientists is that the complexity of constructing the history of evo-devo, let alone projecting its future, is increased by the field's fluid boundaries and shifting focus. Yet these very characteristics are largely responsible for its dynamism, excitement, and promise. It is clearly impossible to erect a rigid retrospective definition of evo-devo, or unambiguously identify its intellectual parentage (although there are multiple, and not mutually consistent, attempts to do so in this volume). It would certainly be a mistake to make such an attempt prospectively—that is, to develop a strict description of what “counts” as evo-devo, or a limited list of questions considered its proper concern. Evo-devo has achieved substantial mainstream success and recognition, including all the essential paraphernalia of an established discipline (dedicated journals, National Science Foundation funding, etc.). Now that the discipline is mature, we have to guard against stodginess; one way to do that may be to resist defining the field too carefully or insisting on a single version of its history.

Griesemer maintains that “the representational openness of 19th-century unifiers…facilitated the diversification of subsequent lines of research” (pp. 400–401). Such openness is equally essential to modern evo-devo if it is to fulfill its ambitious promise of building conceptual continuity from ontogeny through phylogeny: this can occur only through a uniquely broad synthesis of data, ideas, and methodological and epistemological approaches. No one set of tools—not even molecular genetics —will suffice.

Müller contrasts the “explanatory force” of evo-devo with that of traditional evolutionary approaches to some key issues. Moving beyond such direct comparisons, it is clear that the most radically synthetic piece of evo-devo is its attempt to combine two explanatory modes (with very different timescales and notions of causality) in order to address a series of questions that have been important to both evolutionary and developmental biology but addressed adequately by neither (Müller offers a list on pp. 509–510). Modern evolutionary biology, even after the synthesis with genetics, still lacks the “generative component” and “projectability” needed to explain phenomena such as morphological novelty; but without an evolutionary context, no amount of Entwicklungsmechanik, or developmental genetics, can even discern novelty, let alone explain how it occurs or why it matters.

The ultimate ambition or “promise” of evo-devo is to achieve full conceptual continuity between evolutionary and developmental mechanisms and explanations—that is, to generate “a conceptually continuous narrative that connects the molecular processes which create genetic variation, the developmental processes which lead to phenotypes, their function, and the population genetic processes which ultimately effect evolutionary change” (Wagner, p. 539). But close examination of the canonical examples, such as Hox genes or vertebrate limbs, reveals critical gaps. We know a lot about limb development and a lot about the pattern of the fin-limb transition, but we still do not know exactly what embryological changes were directly responsible for evolutionary changes in morphology, and we lack direct “proof of the mechanistic efficacy of the identified molecular changes” (p. 532). More fundamentally, we are not in agreement on what would count as evidence for specific developmental changes serving as direct causes of particular evolutionary variations.

Especially challenging—Wagner suggests it may even be impossible—is combining the radically different timescales and conceptions of causality from evolutionary and developmental biology. The handful of beautiful examples we now have offers some hope that this synthesis is possible, and some models of how to go about it (I'd add finch beaks [Abzhanov et al. 2006] to Wagner's list on pp. 530–531, which includes Drosophila microevolution, quantitative trait locus analysis of stickleback skeletal evolution, and angiosperm phytochromes). But we need more, and that is going to require a combination of groundbreaking ideas and extraordinary technical expertise.

It is also going to require people who are both trained and inclined to make connections well beyond the borders of their own traditionally defined field. Griesemer suggests that the reunification of evolution and development into a coherent whole depends most critically on “instigating [a] realignment of perspectives” (p. 414). This will require both individual polymaths and interdisciplinary collaborations. Even as we struggle to assimilate an overwhelming flood of new information from an ever-broader range of fields, any or all of which might turn out to be important for the evo-devo project, we need to maintain some space for serendipity—like Wallace Arthur's pulling the wrong volume off the shelf and getting Garcia-Bellido and colleagues' work (1979) instead of Kimura's (1979) (an incident described by Wimsatt on p. 333). And having the birds put in a word or two at the ornithology conference may be another way to open up the conversation.

References cited

1.

A. Abzhanov, W. P. Kuo, C. Hartmann, B. R. Grant, P. R. Grant, and C. J. Tabin . 2006. The calmodulin pathway and evolution of integrated beak morphology in Darwin's finches. Nature 442:563–567. Google Scholar

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R. Amundson 2007. An alternative synthesis. Science 318:571–572. Google Scholar

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A. Garcia-Bellido, P. A. Lawrence, and G. Morata . 1979. Compartments in animal development. Scientific American 241:90–98. Google Scholar

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M. Kimura 1979. The neutral theory of molecular evolution. Scientific American 241:98–127. Google Scholar
Jessica A. Bolker "From Embryology to Evo-Devo: A History of Developmental Evolution," BioScience 58(5), 461-463, (1 May 2008). https://doi.org/10.1641/B580515
Published: 1 May 2008
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