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
Evolution of the brain evolution once the divergence between chimpanzees and humans had already occurred. Each of the gene sequences went through specific changes that led to the evolution of humans from ancestral relatives. In order to determine these alterations, Lahn and his colleagues used DNA sequences from multiple primates then compared and contrasted the sequences with those of humans. Following this step, the researchers statistically analyzed the key differences between the primate and human DNA to come to the conclusion, that the differences were due to natural selection. The changes in DNA sequences of these genes accumulated to bring about a competitive advantage