George C. Williams (biologist) 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 on Williams' ideas in this area in the book "The Selfish Gene". Williams was also well known for his work on the evolution of sex, and was an advocate of evolutionary medicine. In later books, including "Natural Selection: Domains, Levels and Challenges", Williams softened his views on group
The Selfish Gene unit of heredity." However, he continues in a later chapter: Dawkins' later formulation is in his book "The Extended Phenotype" (1982), where the process of selection is taken to involve every possible phenotypical effect of a gene. Stephen Jay Gould finds Dawkins' position tries to have it both ways: The view of "The Selfish Gene" is that selection based upon groups and populations is rare compared to selection on individuals. Although supported by Dawkins and by many others, this claim continues to be disputed. While naïve versions of group selectionism have been disproved, more sophisticated formulations make accurate predictions in