The Evolution of Cooperation insects, where the workers – which are sterile, and therefore incapable of passing on their genes – benefit the queen, who is essentially passing on copies of "their" genes. This is further elaborated in the "selfish gene" theory of Richard Dawkins, that the unit of evolution is not the individual organism, but the gene. (As stated by Wilson: "the organism is only DNA's way of making more DNA.") However, kinship selection works only where the individuals involved are closely related; it fails to explain the presence of altruism and cooperation between unrelated individuals, particularly across species. In a 1971 paper
Vestiges of the Natural History of Creation a very wide circulation. Darwin even suggested that Chambers' book helped pave the way for the publication of his theory of evolution by natural selection. "In my opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views." The harsh reception that "Vestiges" received, and the mockery which was made of its evolutionary ideas, has been cited by some historians as a factor leading to Darwin's caution in publishing his own theory of evolution. In a letter to Thomas Henry Huxley