12. Reconceiving Animals and Their Evolution: On Some Consequences of New Research on the Modularity of Development and Evolution 1 Richard M. Burian The last fifteen years have seen an ongoing synthesis among developmental biology, evolutionary biology, and molecular genetics. 2 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 multi-leveled modular parts, many also ancient, yielding organisms whose relationships, because of modular construction, are far more complex and interesting than had been suspected until very 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, non-vitalist form of holism. 1 This is the submission version of the last chapter of my Epistemological Essays on Development, Genetics, and Evolution (New York: Cambridge University Press, 2004). Earlier versions of this chapter were presented at the International Society for History, Philosophy, and Social Studies of Biology and at Ohio University in 2001 and at a Colloquium sponsored by the Virginia Tech Department of Philosophy and Center for Science and Technology Studies in 2002. I am grateful to all three audiences and to numerous colleagues for comments on this and a companion presentation. Colleagues deserving particular thanks are Bill FitzPatrick, Scott Gilbert, Marjorie Grene, Paul Siegel, Günter Wagner, and Lee Zwanziger. Scott Gilbert generously supplied electronic copies of seven of the figures in this chapter. Thanks, Scott! 2 The best single resource for the biology that goes into the new discipline is the last chapter of either of the last two editions of Scott Gilbert’s Developmental Biology (Gilbert 2000, 2003). Gilbert’s book does an extraordinary job of covering the substantial content of present-day developmental biology. This chapter was built using the sixth edition since the seventh arrived too recently for me to take revisions into account. Some other important books written in the last 15 years include (Arthur 1988, 1997, Carroll, Grenier and Weatherbee 2001, Gerhart and Kirschner 1997, Hall 1992, Hall, 1994, Hall 1999, Hall and Olson 2003, Jablonka and Lamb 1995, Keller 2003, Müller and Newman 2003, Pigliucci 2001, Raff 1996, Schlichting and Pigliucci 1998, Wagner 2001, Wilkins 2002).