In his first book, "Adaptation and Natural Selection", 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. This 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".