From the first moments when Charles Darwin began to consider that species might transform over time, he applied his analysis to humans. ‘If all men were dead’, he wrote in his now-famous ‘Transmutation Notebooks’ in 1837, ‘then monkeys make men’.Footnote ¹ And yet, fearing the public backlash with which such claims might be greeted, he did not publish these views immediately. A single line in the conclusion of On the Origin of Species, his most famous work, teased that, via his insights into natural and sexual selection, ‘light will be thrown on the origin of man and his history’, but he said little more in public until a dozen years later.Footnote ² Then, in The Descent of Man and Selection in Relation to Sex, Darwin would be shockingly direct. ‘We thus learn’, he wrote, ‘that man is descended from a hairy quadruped, furnished with a tail and pointed ears, probably arboreal in its habits, and an inhabitant of the Old World’.Footnote ³

While a few complimentary copies, including Darwin's own, were printed in 1870, the two volumes of the Descent were published for purchase on 24 February 1871. The publisher was the prestigious John Murray of London, the third of that name to own the house since its founding in 1768. As an advertisement just before the contents page noted, Murray had previously published Darwin's On the Origin of Species (the fifth edition of which had appeared in 1869), The Variation of Animals and Plants under Domestication (1868), On the Various Contrivances by which British and Foreign Orchids Are Fertilised by Insects (1862), and the second edition of the Journal of Researches into the Natural History and Geology of the Countries Visited during the Voyage of H.M.S. Beagle around the World (1845). An initial issue of 2,500 copies was quickly supplemented by a second, in March, of two thousand, each at a cost of £1 4s. It would be the first of Darwin's books to make a ‘handsome publishing profit’: at the end of September, Murray sent the pleased author a cheque for £1,470.Footnote ⁴

Volume 1, running to over 420 pages, covered the entirety of ‘Part 1: on the descent of man’ and four chapters of ‘Part 2: sexual selection’, while Volume 2, longer by some fifty pages, included the remaining ten chapters and the index. The texts were illustrated by seventy-six woodcuts, marking an obvious visual contrast to the Origin, which had famously contained only a single, branching tree diagram. A second, much altered edition appeared in 1874, now bound as a single volume in three parts. It continued to sell well, with the 35,000th issue of the Murray text appearing in 1899. The year of its first English publication also saw translations into Dutch, German, Russian and Italian, with later translations into French, Danish, Polish and Swedish in Darwin's lifetime and more than a dozen other languages since. As R.B. Freeman noted in 1977, this included two distinct translations into Yiddish – one American, one Polish – at the time at least ‘the only Darwins in this language’.Footnote ⁵

Darwin awaited reviews and responses to the work with trepidation, anticipating, he claimed, ‘universal disapprobation’.Footnote ⁶ The problem was not, as even he admitted in the introduction to the text, the mechanism behind the main theory he had described in Origin. ‘The greater number’ of naturalists, he claimed (and the large majority of the younger generation in particular), ‘accept the agency of natural selection’.Footnote ⁷ The sticking point would be the application of his logics to the descent of man, in particular. Yet, as Moore and Desmond have pithily observed, ‘few howls were heard, merely muffled growls’.Footnote ⁸ Darwin himself suggested in March 1871 that the fact Descent had ‘sold wonderfully’ was ‘proof of the increasing liberality of England’. He had, as yet, faced ‘no abuse’, although, as he added parenthetically, ‘some, no doubt, will come, strong enough’. He found, it is true, few sympathetic reviewers for his claims concerning humanity's descent from a lower life form. That other animals were related to one another might be granted, but man was a special case. Reviewers in The Times, Harper's Weekly, the Edinburgh Review, The Spectator and multiple other journals seemed in accord with a writer in The Guardian, who simply asserted that ‘Holy Scripture plainly regards man's creation as a totally distinct class of operations from that of lower beings.’Footnote ⁹

Overall, however, the dozen years of public battles over evolution that had followed the publication of Origin meant that the response to Descent was more muted than it might once have been. ‘Apes and angels had been dealt with ten or twelve years before’, Janet Browne notes. ‘Faced with a new book about descent in 1871, journalists seemed to find little more to say. They and their readers had become accustomed to the idea of evolution, although not necessarily comfortable with it.’Footnote ¹⁰ That discomfort would persist, for Darwin's Descent did much more than simply apply the logics of Origin to humanity. In one of the most insistently – and at times perversely – naturalistic books of the nineteenth century, he sought to establish that all aspects of humanity have some parallel in lower species. Where many of Darwin's contemporaries could grant that ‘man’ shared his physical form with members of the animal kingdom, they also insisted that humans differed in their intellects and souls. Darwin resisted even this separation. Beasts could think, he posited, could appreciate the rudiments of aesthetics, and could engage in altruistic acts. Animals even exhibited some form of religious understanding. There was no space in Darwin's work for a creator to make a distinction of kind, rather than degree, amongst the myriad of his creations.Footnote ¹¹

In Descent, too, Darwin explicitly drew upon the social mores of his age, naturalizing Victorian assumptions concerning class, race and sex.Footnote ¹² The dismal vision of the British political economist Thomas Malthus had provided an engine driving natural selection: in a population under severe pressure for resources, the ‘fittest’ – in Herbert Spencer's later formulation – would survive in disproportionate numbers. In Descent, Darwin made clear that he shared at least parts of Malthus's moralizing social vision as well. ‘The advancement of the welfare of mankind’, he wrote, ‘is a most intricate problem: all ought to refrain from marriage who cannot avoid abject poverty for their children; for poverty is not only a great evil, but tends to its own increase by leading to recklessness in marriage’.Footnote ¹³

Race was a hinge connecting the two parts of Darwin's book: one on human descent, one on sexual selection. For Darwin, differences between the races were not originary. Against those who argued that humans developed (or were created) in different kinds (and hence that Africans, for example, were not to be regarded as ‘brethren’ to Europeans), Darwin concluded that we were all one, even if he demurred on the claim that humans found their beginnings in a single, Edenic pair. This monogenetic insistence, however, raised new questions. Whence the physical differences between human races? Why were some peoples dark-skinned with black, curly hair, while others were fair and blonde? Darwin rejected the kinds of answers we accept today, arguing that natural selection was insufficient for explaining why some groups of humans at similar latitudes did not exhibit the same skin colour, while those at geographically dispersed latitudes looked remarkably similar. Nor could he establish an adaptive advantage for other racial traits. What kind of ‘fitness’ could be associated with the European male's bushy beard, among the most oft-remarked-upon differences among so-called Caucasians and Negro or Malayan races? Instead – as Evelleen Richards has so elegantly elucidated in Darwin and the Making of Sexual Selection – Darwin argued that selection on the idiosyncratic aesthetic predilections of men and women of all races had produced such differences.Footnote ¹⁴ Women in some isolated European populations over vast spans of time had preferred men with hirsute visages, while aesthetic preferences had gone the other way on the African and Asian continents. Natural selection might explain how we, as a species, came to be distinguished from apes, but it was differential conceptions of beauty that explained how we differed from each other. The association of Darwin with evolutionary theories of human unity and difference spread like wildfire.Footnote ¹⁵

The production, reception and legacy of Charles Darwin's Descent of Man and Selection in Relation to Sex (1871) are marked by scientists’ direct engagement with questions of race, sex, class and sexuality – in essence, those familiar characteristics which were taken to mark humanity.Footnote ¹⁶ Whether in spite or because of Darwin's own clear and fascinating borrowings from the social realm, Descent has received much less scholarly attention than Origin; the materials that make up the extensive Darwin literature are concerned primarily with the production and reception of Darwin's theory of natural, rather than sexual, selection.Footnote ¹⁷ In the last decade, sexual selection has piqued scientific and historical interest, drawing on long-standing scholarship exploring the naturalization of sex and race.Footnote ¹⁸ Much of this literature has tackled questions of either sex and gender or race and human descent, yet, as Richards's Darwin and the Making of Sexual Selection so clearly shows, for Darwin these questions were mutually constitutive.Footnote ¹⁹ In her analysis, Darwin's experience on board the HMS Beagle launched him on a quest to understand the naturalistic process governing the development of aesthetic preferences in humans and animals – at issue were the relative standards of beauty held by racialized groups.Footnote ²⁰ He first used the term ‘sexual selection’ in his notes as he grappled with Robert Knox's Races of Men.Footnote ²¹ Although he had planned to include substantial material on sexual selection in his ‘big species book’, when he rushed Origin into print he whittled his discussion of mate choice and competition down to a single chapter, which enabled him to postpone until later – what would become Descent – his discussion of human evolution.Footnote ²² By bringing together historians invested in the history of evolution, race, sex and human nature, this volume explores the forest of interpretations that have grown from these Darwinian seeds in the last century and a half.

In the years since 1871, scientists and scholars around the globe have debated and deployed Darwin's Descent in myriad contexts. From the woman question of the late nineteenth century to the concerns of evolutionary psychology in the late twentieth, scientists have continued to utilize Darwin's writings as an intellectual resource in seeking answers to questions of humanity's essential nature. Over the course of the intervening century, Darwin's theories served to explain and naturalize differences across the political spectrum. Eugenicists and others pointed to women and people racialized as non-white as less evolved or evolved differently. Progressive Era feminists invoked female choice to argue that they should be given more social responsibility than men, not less.

The idea that humans had evolved from ape-like ancestors, too, remained intimately associated with Darwin's name, even though he was neither the first nor the most recent naturalist to discuss the ‘descent’ or (more frequently) ‘ascent’ of man.Footnote ²³ Other scientists, however, quickly abandoned his notion that sexual selection had created human ‘races’ and instead associated human evolution with the theory of descent, or organic evolution, broadly conceived. Sexual and natural selection as applied to human nature did stick in two ways: in interpreting differences between the sexes and in the possibility of controlling humanity's future, both of which depended on mate choice.Footnote ²⁴ That Darwin had engaged explicitly with questions of race, sex and class in human evolution indelibly linked these ideas with his name but not necessarily with Descent, and provided leverage for differentiating between the modern and the uncivilized.Footnote ²⁵ By tracing the appropriation of Darwin's ideas, the essays in this volume make evident the crucial role played by Descent even when authors cited Origin as the key reference to Darwin's understanding of race, animality, sex and human nature.

Three essays explore the creation and reification of racial categories as a function of Darwinian theory. In the careful attention paid to the reproduction of enslaved people and contemporary theories of hybridization, issues of sex and race were bound intimately to each other long before Darwin published Descent. Myrna Perez Sheldon argues that Darwin transformed this connection into causality, seeing sexual reproduction as a mechanism explaining the origins of races. Thus sex became as integral to evolutionary theories as it was to the governing principles of modern nation states. Suman Seth picks up this thread, exploring how Darwin's theory of racial construction came only after he eliminated other possibilities, especially the idea that dark skin could be correlated with certain kinds of disease immunity. In the nineteenth century, Seth contends, medicine was a crucial site for forging ideas about race. Among the questions Darwin considered most deeply was that of the single or multiple origins of the human species.Footnote ²⁶ Marianne Sommer shows that the high stakes of this debate informed Descent's visual language as well as its prose. As noted earlier, Descent was generously illustrated, reflecting the rich nineteenth-century visual culture depicting sexualized and racialized subjects for public consumption. Darwin had intended that one of these figures would depict the evolutionary relationships between primates. In the end, Darwin decided against including it, and Sommer posits in her paper that his reluctance stemmed from the image's concrete representation of an abstract set of relationships. Once printed, he feared, it would imply racial hierarchies and an inherent teleology he was keen to avoid. Race suffused Darwin's understanding of sex and history, as Sheldon, Seth and Sommer amply demonstrate.

Sexual selection, for Darwin, explained as much about animals as it did about humans, by illustrating their deeply entwined fates. In his paper, Projit Bihari Mukharji explores Darwin's fascination with the diversity of South Asian birds and the ways that sexual selection emerged from the colonial realities of ornithology. Information about birds flowed along the routes of imperial travel, taken from Victorian India and transformed into data. Gregory Radick and Mark Steadman attend to voyages of a different sort, starting with the men and lice on board the HMS Beagle. For Darwin, the apparent association of different species of lice with different races provided a platform for working through the relationship between varieties and species identity. In light of these slippages between humanity and animality, the capacity for true language remained a key dividing line. Judith Kaplan explores how linguists sought to understand the origins of language in human history, rendering this distinction equally porous in the evolutionary linguistics of the Cold War.

Returning to the turn of the century, Kimberly Hamlin argues that Darwin's ideas in Descent – about sex, race and human evolution – found fertile intellectual ground among radical freethinkers, socialists and feminists. Their fascination with and appropriation of Darwin's ideas, Hamlin suggests, served to make them appear even more scurrilous to the scientific establishment and help account for the lack of citations of Descent, even as biologists themselves continued to wrestle with the same ideas and concepts. In attending to questions of sexuality, Erika Lorraine Milam then explores how evolutionary biologists of the late twentieth century applied evolutionary theories to the origin of homosexuality as a biological phenomenon. For most of the century, she argues, these theories relied on comparisons between humans and a finite number of animal species; however, more recently arguments for marriage equality have emphasized the diversity of sexualities across the animal kingdom. Together, Hamlin's and Milam's papers illustrate the power that Darwin's theories in Descent held for scientists and activists seeking to make sense of their contemporary society.

The final set of papers turns to human nature, with Piers Hale tackling the question of Darwin's politics, and especially how sexual selection underpinned Darwin's writings on the origins of other-regarding ethics in humans. Although Darwinism has often been associated with theories of racism and sexism, Hale argues, there is a tradition, too, in finding in Darwin's theories the promise of moral worth in all sentient beings, human and non-human alike. Nasser Zakariya unearths the ways in which the evolutionary process – for authors in the 1870s and beyond – represented a compromise of antagonistic forces: natural and sexual selection, ethics and survival, morality and intelligence. Resolving these forces required reconciling conflicting notions of progress that shifted with political and historical context. Such negotiations also characterized the reception of ideas about reproduction, eugenics and human evolution in China, as charted by Lijing Jiang. She shows how a prominent eugenicist and an embryologist keen to improve the Chinese race and nation argued for the application of evolutionary theory to humanity but downplayed Descent in their publications.

In sum, the social and intellectual influence of Descent of Man and Selection in Relation to Sex far exceeded direct citations of and references to Darwin's work by the scientific community. Indeed, sexual selection remains a powerful logic through which scientists today seek to make new sense of the raced, sexed and classed world in which they live.Footnote ²⁷ Darwin's obsessions are ours too. To fully grasp the long-term perceived relevance of these ideas to our modern understandings of what makes us human, we must wrestle with the polymorphous political flexibility of evolutionary theories of humanity. Yes, evolutionary theory has been used to separate people and reify difference in biological language – we know this story well – but scientists and social activists alike have also mobilized evolution in the service of progressive, even radical, political stances. Together the essays of this volume powerfully illustrate this diversity, allowing us to see, with the benefit of historical hindsight, the impossibility of reducing any biological insight to a single social interpretation. Power, hope and danger all lurk in the naturalizing promise of evolutionary understandings of human behavior.