The Descent of Man, and Selection in Relation to Sex

Darwin's central argument is that humans are not a separate creation but descended from some pre-existing, lower form, and that the mental and moral differences between humans and other animals are of degree, not kind. He rejects the assumption that human origins can never be known scientifically, arguing that ignorance more often begets confidence than knowledge. The book's second major claim is that sexual selection—competition for mates and mate choice—has played a powerful role in shaping human racial differences and secondary sexual characteristics, a mechanism Darwin felt had been neglected in the Origin. The work thus extends his general evolutionary framework to the species he had previously left aside, treating humans as continuous with the rest of nature.

Darwin's assertions about race and sex are not incidental asides but embedded in his evolutionary argument. He portrayed Indigenous peoples of the Americas and Australia as less than Europeans, and Africans as cognitively depauperate and lower in rank. He described women as less capable than white men, often akin to the 'lower races,' invoking natural and sexual selection as justification despite lacking concrete data. Agustín Fuentes argues that these claims are 'dismally, and dangerously, wrong' and that the book offers a racist and sexist view of humanity. Modern readers should approach the text as one from which to learn, not to venerate—acknowledging its innovative insights while refusing to uncritically accept its harmful assertions.

Sexual selection is Darwin's theory that certain traits evolve not because they aid survival but because they improve access to mates—either through same-sex competition or through mate choice. In The Descent of Man, Darwin argued that sexual selection explains many striking features in the animal kingdom that appear detrimental to survival, such as the peacock's tail. He then applied this mechanism to humans, proposing that differences between races—skin color, hair texture, facial features—originated from sexual selection, with different groups developing different standards of beauty and preferences for particular physical characteristics. He admitted being 'baffled' by attempts to explain racial differences through natural selection alone, and saw sexual selection as the remaining important agency.

The 1874 second edition was substantially revised and augmented. Darwin reorganized the book into three parts—'The Descent or Origin of Man,' 'Sexual Selection,' and 'Sexual Selection in Relation to Man and Apes'—added forty pages of new material, a preface, and a table listing additions and corrections. He also appended Thomas Henry Huxley's 'Note on the Resemblances and Differences in the Structure and Development of the Brain in Man and Apes' as the conclusion of part one. The second edition was published as a single volume at a reduced price, making it more accessible. This pattern—expanding evidence, reorganizing structure, and incorporating allies' contributions—reflects Darwin's method of responding to criticism through accumulated data and careful argumentation rather than concession.

The claims that have held up are foundational: humans share common ancestry with other primates, differences between humans and animals are of degree rather than kind, and cooperation and social learning are central to human evolution. Darwin's recognition of these points was trailblazing and remains core to human evolutionary studies. The claims that have not held up are his assertions about racial hierarchy and female intellectual inferiority. Modern science has demonstrated unequivocally that race is not a valid description of human biological variation, that there is no biological coherence to 'male' and 'female' brains, and that 'survival of the fittest' does not accurately represent evolutionary dynamics. The book thus presents a mixed legacy: innovative and insightful in its broad framework, deeply flawed in its specific application to human difference.

Later research has confirmed Darwin's insight that mate choice makes a primary contribution to sexual selection, but has fundamentally revised his account of who does the choosing and why. Darwin's misogyny precluded serious analysis of female 'taste,' and he emphasized male competition and female passivity. Modern research shows that both males and females exercise mate choice, often through mechanisms that occur after mating as well as before, and that preferences evolve for reasons that may have little to do with sexual selection on chosen traits. Mate choice may be more about choosing compatible partners than picking the 'best' mate in absolute terms, and compatibility-based choice can drive genetic divergence. This represents both a confirmation of Darwin's core insight and a rejection of his gendered framing of it.