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 Genius evolutionary theory that portrays natural selection as acting at the level of the individual gene to the exclusion of group selection models which state that it could also act at the level of organisms or species. The book also claims Dawkins embraces an outdated and prescriptive conception of evolution that actually restricts debate rather than promoting it. The book has provoked controversy with some online commentary claiming it is another 'flea', a term used by Dawkins to describe people who have published books about him or his ideas. An article by Fern Elsdon-Baker in "New Scientist" of 19 July 2009