12 - Reconceiving Animals and Their Evolution: On Some Consequences of New Research on the Modularity of Development and Evolution

Summary

The last fifteen years have seen an ongoing synthesis among developmental biology, evolutionary biology, and molecular genetics. A new discipline, “evolutionary developmental biology,” is forcing biologists to reconceive evolutionary history, evolutionary processes, and the ways in which animals are constructed. In this chapter, I examine some work bearing on how animals (including humans) are put together. A key claim is that evolution deploys ancient modular processes and tinkers with multileveled modular parts, many also ancient, yielding organisms whose relationships – because of modular construction – are far more complex and interesting than had been suspected until recently. For example, all segmented animals share regulatory machinery that demarcates and specifies identities of body segments and switches on the formation of some organs (e.g., eyes). Some processes, bits of machinery, and parts are recycled and reused repeatedly, both in evolution and in development of a single animal. Such claims require major rethinking of how animals are put together and raise issues about how – and the extent to which – animals are harmoniously integrated. Our understanding of how synchronic and sequential developmental processes are controlled to yield an organism is still far from complete. We do not yet understand the philosophical implications of this new work, but I suggest that they include a limited, nonvitalist form of holism.