The book came five years after Charles Darwin and Alfred Russel Wallace announced their theory of evolution by means of natural selection, and four years after the publication of Darwin's "Origin of Species". In the "Origin" Darwin had deliberately avoided tackling human evolution, except for a sentence: "Light will be thrown on the origin of man and his history". Darwin's sequel came eight years later, with "The Descent of Man, and Selection in relation to Sex" (1871).