El origen del hombre
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, but left a gnomic trailer: "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).