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
Gene-centered view of evolution organisms containing the same allele (kin altruism and green-beard effects), or even its own propagation relative to the other genes within the same organism (selfish genes and intragenomic conflict). The gene-centered perspective can be traced to the philosopher Henri Bergson who wrote, in his book, ‘Creative Evolution’ (1907): ‘Life is like a current passing from germ to germ through the medium of a developed organism. It is as if the organism itself were only an excrescence, a bud caused to sprout by the former endeavouring to continue itself in a new germ’. The gene-centered view of evolution is a model