Williams, in what is now considered a classic by evolutionary biologists,[1] outlines a gene-centered view of evolution,[2] disputes notions of evolutionary progress, and criticizes contemporary models of group selection, including the theories of Alfred Emerson, A. H. Sturtevant, and to a smaller extent, the work of V. C. Wynne-Edwards.

"[3] Though more technical than a popular science book, its target audience is not specialists but biologists in general and the more advanced students of the topic.

If something is considered (after critical appraisal) to be an adaptation, then we should assume the unit of selection in the process was as simple as possible, provided it is compatible with the evidence.

Elaborating on the nature of selection, he writes that it only works on the basis of whether alleles are better or worse than others in the population, in terms of their immediate fitness effects.

The author concludes that his view on the topic is similar to that of most of his colleagues, but worries that it is misrepresented to the public "when biologists become self-consciously philosophical".