Modern synthesis (20th century) a gene-centred view of evolution following Hamilton's concepts, disputing the idea of evolutionary progress, and attacking the then widespread theory of group selection. Williams argued that natural selection worked by changing the frequency of alleles, and could not work at the level of groups. Gene-centred evolution was popularised by Richard Dawkins in his 1976 book "The Selfish Gene" and developed in his more technical writings. In 1975, E. O. Wilson published his controversial book "", the subtitle alluding to the modern synthesis as he attempted to bring the study of animal society into the evolutionary fold. This appeared radically new,
Alternatives to evolution by natural selection denied, explanations of evolution such as Lamarckism, catastrophism, orthogenesis, vitalism, structuralism and mutationism (called saltationism before 1900) were entertained. Different factors motivated people to propose non-Darwinian mechanisms of evolution. Natural selection, with its emphasis on death and competition, did not appeal to some naturalists because they felt it immoral, leaving little room for teleology or the concept of progress in the development of life. Some who came to accept evolution, but disliked natural selection, raised religious objections. Others felt that evolution was an inherently progressive process that natural selection alone was insufficient to explain. Still others felt that nature, including