Abstract

Evolutionary Biology has two principal explananda, fit and diversity (Lewontin 1978). Natural selection theory stakes its claim to being the central unifying concept in biology on the grounds that it demonstrates both phenomena to be the consequence of a single process. By now the standard story hardly needs reiterating: Natural selection is a force that operates over a population, preserving the better fit, culling the less fit, and along the way promoting novel solutions to adaptive problems. Amundson’s historical survey of the concept of adaptation captures the idea succinctly: The phenomenon of adaptation is at the core of modern evolutionary biology. Natural selection, the mechanism universally regarded as the primary causal influence on phenotypic evolutionary change, is first and foremost an explanation of adaptation. (1996: 11) At the same time, it appears that the capacity of natural selection to cause adaptations cannot account for every feature of the nature and distribution of biological form. Reason to believe this devolves from the simple fact that the bearers of biological form are organisms and a salient fact about organisms is that each faces the tribunal of the environment as a corporate entity, not as a loose aggregate of independent traits. One consequence of this fact is that at each stage of its development from egg to adult an organism must be an integrated, functioning whole. Another is that for any form to arise in an organism at a time, it must develop from the materials and processes at the organism’s disposal. The requirement of integration and the processes of development that produce it leave their distinctive marks on form. It seems reasonable, then, to suppose that one might appeal to the processes of development and the principles by which they operate in explaining the nature and distribution of biological form. (See here Gould 1977; Rose and Lauder 1996).