Williams's 1957 paper
Pleiotropy, Natural Selection, and the Evolution of Senescence is one of the most influential in 20th-century evolutionary biology, and contains at least three foundational ideas. The central hypothesis of
antagonistic pleiotropy remains the prevailing evolutionary explanation of senescence. In this paper, Williams was also the first to propose that
senescence should be generally synchronized by
natural selection. According to this original formulation ... if the adverse genic effects appeared earlier in one system than any other, they would be removed by selection from that system more readily than from any other. In other words, natural selection will always be in greatest opposition to the decline of the most senescence-prone system. This important concept of synchrony of senescence was taken up a short time later by
John Maynard Smith, and the origin of the idea is often misattributed to him, including in his obituary in the journal
Nature. Finally, Williams's 1957 paper was the first to outline the "
grandmother hypothesis". Williams's formulation stated that natural selection might select for menopause and post-reproductive life in females (though not explicitly mentioning grandchildren or the
inclusive fitness contribution of grand-parenting). In his first book,
Adaptation and Natural Selection (1966), Williams advocated a "ground rule - or perhaps
doctrine would be a better term - ... that
adaptation is a special and onerous concept that should only be used where it is really necessary", and that, when it is necessary,
selection among
genes or individuals would in general be the preferable explanation for it. He elaborated this view in later books and papers, which contributed to the development of a gene-centered view of evolution.
Richard Dawkins built upon Williams's ideas around selection and genes in his book
The Selfish Gene (1976). Williams was also well known for his work on the
evolution of sex, and was an advocate of
evolutionary medicine. In
Sex and Evolution (1975), he attempted to explain why many species use exclusive sexual reproduction despite its “twofold cost". He proposed several explanatory models ( “aphid-rotifer model,” the “strawberry-coral model,” and “elm-oyster model"), though found all of them insufficient. He even considered the possibility that sex is a maladaption for some species:When major taxonomic groups all share a certain feature, it is unlikely that the feature has the same adaptive significance throughout the group. It may even be maladaptive for the majority... The fact that parthenogenesis or its equivalent, if found in a vertebrate population, has always replaced sexual reproduction entirely, is decisive evidence of the maladaptive nature of sexuality in these organisms. (Chapter 9)In later books, including
Natural Selection: Domains, Levels and Challenges, Williams softened his views on group selection, recognizing that
clade selection,
trait group selection and
multilevel selection did sometimes occur in nature, something he had earlier thought to be so unlikely it could be safely ignored. Williams became convinced that the genic neo-Darwinism of his earlier years, while essentially correct as a theory of microevolutionary change, could not account for evolutionary phenomena over longer time scales, and was thus an "utterly inadequate account of the evolution of the Earth's biota" (1992, p. 31). In particular, he became a staunch advocate of clade selection – a generalisation of species selection to monophyletic clades of any rank – which could potentially explain phenomena such as adaptive radiations, long-term phylogenetic trends, and biases in rates of speciation/extinction. In Natural Selection (1992), Williams argued that these phenomena cannot be explained by selectively-driven allele substitutions within populations, the evolutionary mechanism he had originally championed over all others. This book thus represents a substantial departure from the position of Adaptation and Natural Selection. ==Academic career==