The influence of development on evolutionary dynamics: A theoretical investigation.

Abstract

Development is the process by which genes build organisms. It thus determines how genetic variation is translated into phenotypic variation. The dynamics of evolution are therefore determined not only by the action of selection and drift, but also by the processes by which organisms are built. I present a general model with which to study how selection acts on a developmental program. This model explains, and clarifies, the trend towards conservatism in early development. Furthermore, it predicts that this conservatism will be reduced under certain environmental conditions, namely when fitness functions are fluctuating. This leads to the prediction of the pattern of nearshore innovation seen in the fossil record. A more careful test of the theory requires a system in which we have some understanding of the details of development. I provide this in the form of a model of shell growth in mollusks. This model predicts shell form as a function of the interactions between shell producing tissues during growth. Using this system, I test the prediction of the general model that characters that are not correlated with, but not independent of, many other characters should evolve slowly. This prediction is upheld by data gathered from 8 genera of marine gastropods.