Unit of selection and Confirmation of Evolutionary Theory" provides a basic "philosophical" introduction to the debate. Below, cases of selection at the genic, cellular, individual and group level from within the multi-level selection perspective are presented and discussed. George C. Williams in his influential book "Adaptation and Natural Selection" was one of the first to present a gene-centered view of evolution with the gene as the unit of selection, arguing that a unit of selection should exhibit a high degree of permanence. Richard Dawkins has written several books popularizing and expanding the idea. According to Dawkins, genes cause phenotypes and a gene is
Gene-centered view of evolution views selection as working on many levels, and has called attention to a hierarchical perspective of selection. Gould also called the claims of "Selfish Gene" "strict adaptationism", "ultra-Darwinism", and "Darwinian fundamentalism", describing them as excessively "reductionist". He saw the theory as leading to a simplistic "algorithmic" theory of evolution, or even to the re-introduction of a teleological principle. Mayr went so far as to say "Dawkins' basic theory of the gene being the object of evolution is totally non-Darwinian." Gould also addressed the issue of selfish genes in his essay "Caring groups and selfish genes". Gould acknowledged that Dawkins was