Conceptual and Epistemological Foundations of Developmental Evolution

Our projects in the history of evolutionary, theoretical and developmental biology offers a much richer and more diverse picture than the standard narrative “From Darwin to Evo Devo” suggests. Furthermore, many of these previously neglected episodes shed new light on current developments in evolutionary theory. The possibilities enabled by the emerging causal-mechanistic understanding of phenotypic evolution arguably represent the most dramatic transformation of evolutionary theory in decades. Yet the roots of this conceptual re-orientation of evolutionary biology can only partially be found within the mainstream history of the field as it has been portrayed so far. Rather the antecedents of much of this work fall within the alternative tradition wet are exploring. As a result, the history of evolutionary biology increasingly resembles our current understanding of evolutionary history; we no longer see a linear or simple branching pattern, with one “progressive” trunk and major and minor branches diverging from it. Quite the opposite, we see the same reticulate pattern and horizontal as well as vertical transmission of ideas (genes/memes) that characterizes the majority of evolutionary events (especially in the microbial domain).

Having a more complete understanding of the history of evolutionary theory since Darwin has important practical implications. Early 21st century evolutionary biology emphasizes the need for synthesis, either as a “completion of the Modern Synthesis” or in form of a new synthesis. Both of these calls require the integration of radically different conceptual frameworks, experimental traditions, fundamental assumptions and epistemologies in order to achieve a more inclusive understanding of the evolutionary process. Without successful integration of the different domains of developmental and evolutionary biology the developmental evolution or Evo Devo project will fail. After an initial period of enthusiasm the field has now entered a phase of routine data generation. What is still largely left undone is the hard work of conceptual integration that is required for a true theoretical synthesis.

In this context critical historical perspectives are essential. They will enable us to evaluate the often hidden assumptions of certain models and concepts. The examples discussed here can serve as an illustration. Do we build our new synthesis of 21st century evolutionary biology within the conceptual framework of population-based adaptive dynamics—which implies that developmental mechanisms feature as an explanation of the genotype-phenotype map, or do we represent the evolutionary process within a causal-mechanistic framework that can be captured by the following logical structure: (1) All phenotypes are the product of developmental mechanisms; (2) all phenotypic variation is therefore a consequence of a corresponding variation in the developmental process; (3) understanding these developmental processes provides a causal-mechanistic explanation for the origin of phenotypic variation (Darwin’s first question); (4) the subsequent fate of phenotypic variation can be analyzed within the population-based framework of adaptive dynamics.

To fully appreciate the differences between these two proposed versions of a 21st century synthesis of evolutionary theory we need to understand how each of those viewpoints emerged historically and what epistemological assumptions guide the integration of developmental and evolutionary perspectives. As we have seen, the possibilities of synthetic experimental evolution represent a significant addition to the standard experimental repertoire of evolutionary biology, which is no longer confined to comparative and functional analysis or selection experiments. The ability to reconstruct major phenotypic transitions in evolutionary history through the manipulation of the underlying developmental mechanisms turns evolutionary biology into a mechanistic science. One consequence of this emerging transformation of evolutionary biology is that the standard distinction between proximate and ultimate causes no longer serves as the most obvious way to separate explanatory paradigms within (evolutionary) biology.

Evolutionary biology thus continues to evolve. And insofar as embryological considerations were already central to the earliest formulations of evolutionary theory, the current resurgence of developmental approaches reveals some of the deep conceptual structures at the core of evolutionary thought that we are exploring in the context of this project.