Introduction

I've known Dick Lewontin since the early 1960s. Hardly a month has passed in that time in which I've not made use of one or another of his contributions to evolutionary biology. That does not mean, as “the literature” bears witness, that he and I have always been in agreement! But we have been deeply interested in many of the same questions. So, it is a pleasant challenge for me to recount here some work on evolutionary processes that I and my associates have done. The mechanistic study of evolution, as we understand it, entails a central focus on adaptation, i.e., on organism–environment interactions, as a basis for predicting demographically based fitness outcomes (or their absence). Thus I begin by stating our views of the place of adaptation in the evolutionary process. I next turn to illustrative empirical examples from our work, and then to discussion of some general evolutionary questions of common interest, whose answers these examples illuminate.

The adaptation concept and its role in the study of evolution

Adaptation, correctly understood, refers to the suitedness of heritably varying phenotypes to the range of environments they occupy, and hence to these phenotypes differential performance of biological function in those environments (Watt 1994, 2000, 2001).