A lineage is expected to evolve to maximise its inclusive fitness—the number of copies of its genes passed on globally (rather than by a particular individual). As a result, populations will tend towards an evolutionarily stable strategy. The book also coins the term meme for a unit of human cultural evolution analogous to the gene, suggesting that such "selfish" replication may also model human culture, in a different sense. Memetics has become the subject of many studies since the publication of the book. In raising awareness of Hamilton's ideas, as well as making its own valuable contributions to the field, the book has also stimulated research on human inclusive fitness.
In the foreword to the book's 30th-anniversary edition, Dawkins said he "can readily see that might give an inadequate impression of its contents" and in retrospect thinks he should have taken Tom Maschler's advice and called the book The Immortal Gene.
In July 2017, The Selfish Gene was listed as the most influential science book of all time in a poll to celebrate the 30th anniversary of the Royal Society science book prize.
Dawkins builds upon George C. Williams's book Adaptation and Natural Selection (1966), which argued that altruism is not based upon group benefit per se, but is a result of selection that occurs "at the level of the gene mediated by the phenotype" and any selection at the group level occurred only under rare circumstances. This approach was developed further during the 1960s by W. D. Hamilton and others who opposed group selection and selection aimed directly at benefit to the individual organism:
Despite the principle of 'survival of the fittest' the ultimate criterion which determines whether G will spread is not whether the behavior is to the benefit of the behaver, but whether it is to the benefit of the gene G ...With altruism this will happen only if the affected individual is a relative of the altruist, therefore having an increased chance of carrying the gene.