Introduction

The two most striking facts about the living world that Darwin attempted to explain were that organisms are so often superbly fitted for survival and reproduction, and that living things display a staggering diversity of different forms. In principle, the two facts could be explained independently of one another (as Lamarck believed they should), but if a significant part of the explanation of the latter fact is that species have diversified in the course of adapting to different environmental challenges, then adaptation becomes the central Darwinian concept for explaining both good design and diversity. Familiarity with the career of adaptationist explanations, therefore, becomes critical to understanding the evolution of Darwinism.

As we saw in the previous chapter, Darwin's view of adaptation underwent a significant shift from his earlier view (influenced by theological considerations) that organisms were perfectly designed, to his later view (developed in light of his understanding of the operation of natural selection) that organisms are at best only relatively well adapted to their circumstances. As Darwin was moving from a notion of absolute to a notion of relative adaptation, his ally and intellectual sparring partner Alfred Russel Wallace was becoming a strict selectionist-adaptationist for whom every feature of every organism (with one notable exception, to be discussed in Chapter 10) has resulted from present or past utility.