The Descent of Man, and Selection in Relation to Sex

The Descent of Man, and Selection in Relation to Sex was a book on evolutionary theory by British naturalist Charles Darwin, first published in 1871. It was Darwin's second large book on evolutionary theory, following his 1859 work, The Origin of Species, and is concerned with outlining explicitly the application of Darwin's theory to human evolution, and outlining in detail the theory of sexual selection.

Darwin's background issues and concerns

Charles Darwin's Origin of Species had been met with a firestorm of controversy in reaction to Darwin's theory, largely because it was clear that it implied that human beings were evolved from animals, contradicting the story of Genesis and implying an animal nature. Darwin had not made the link explicit in Origin, though; a single line hinted at such a conclusion: "light will be thrown on the origin of man and his history". But the conclusion was fairly obvious to his contemporaries, and became the subtext if not the center of many debates over his theory (such as those between T.H. Huxley and Richard Owen over the brains of apes). When writing The Variation of Animals and Plants Under Domestication in 1866, Darwin intended to include a chapter including man in his theory, but the book became too big and he decided to write a separate "short essay" on ape ancestry, sexual selection and human expression which became The Descent of Man.

Related Topics:
Reaction to Darwin's theory - Genesis - T.H. Huxley - Richard Owen - 1866 - Sexual selection

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Darwin's writing on the subject in The Descent of Man came twelve years after his work on Origin, and was by no means the first work on human evolution. As such, the book is a response to various debates of Darwin's time far more wide-ranging than the questions he raised in Origin. It is often erroneously assumed that the book was controversial because it was the first to outline the idea of human evolution and common descent. Coming out so late into that particular debate, while it was clearly Darwin's intent to weigh in on this question, his goal was to approach it through a specific theoretical lens (sexual selection) which had previously been undiscussed by the other commentators at the period, as well as considering evolution of morality and religion. The theory of sexual selection was also needed to counter the argument that beauty with no obvious utility such as exotic birds' plumage proved divine design, which had been put strongly by the Duke of Argyll in his book The Reign of Law.

Related Topics:
Common descent - Duke of Argyll

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See Darwin from Descent of Man to Emotions for the context and Darwin's sources when writing this book.

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Human faculties

The major sticking point for many in the question of human evolution was whether or not human mental faculties could have possibly been evolved. The gap between humans and even the smartest ape seemed too large even for those who were sympathetic to Darwin's larger theory. Alfred Russel Wallace, the "co-discoverer" of evolution by natural selection, believed that the human mind was too complex to have evolved gradually, and began over time to subscribe to a theory of evolution which took more from spiritualism than it did the natural world. Darwin was deeply distressed by Wallace's change of heart and much of the Descent of Man is in response to opinions put forth by Wallace. Darwin focuses less on the question of whether humans evolved as it does on displaying that each of the human faculties considered to be so far beyond those of animals—such as moral reasoning, sympathy for others, beauty, and music—can be seen in kind (if not degree) in other animal species (usually apes and dogs).

Related Topics:
Alfred Russel Wallace - Natural selection - Spiritualism

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Human races

The questions of what "race" was, how many human races there were, and whether they could be "mixed", were key debates in the nascent field of anthropology in Darwin's time. After the American Civil War (1861-1865), the question of race and slavery were brought to the forefront in anthropology in the United States and Europe. Many scientists from the Southern U.S. were publishing long monographs on why the "Negro" was inferior and would soon be driven to extinction by newfound freedom, with an implication that slavery had been not only "beneficial" but "natural". Darwin was a long-time abolitionist who had been horrified by slavery when he first came into contact with it in Brazil while touring the world on the Beagle voyage many years before, and considered the "race question" one of the most important of his day. Darwin took a radical view for his time—that all human beings were of the same species, and that races, if they were useful markers at all, were simple "sub-species" or "variants." This view (known as "monogenism") was in stark contrast with the majority view in anthropology at the time, that the different human races were distinct species or sub-species ("polygenism"). Polygeny was supported by thinkers of many backgrounds, such as the Creationist Louis Agassiz, and by later thinkers who would interpret Darwin's theory to imply that races had been evolved at different times or stages. Darwin's own views of this were that the differences between human races were superficial (he discusses them only in terms of skin color and hair style), and much of Descent is devoted to the question of the human races. Aside from the aforementioned encounter with slavery on the Beagle, Darwin also was perplexed by the "savage races" he saw in South America at Tierra del Fuego, which he saw as evidence of a man's more primitive state of civilization. During his years in London, his private notebooks were riddled with speculations and thoughts on the nature of the human races, many decades before he would publish Origin.

Related Topics:
Race - Anthropology - American Civil War - 1861 - 1865 - Negro - Slavery - Brazil - Beagle voyage - Species - Polygenism - Creationist - Louis Agassiz - Tierra del Fuego

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Social implications of Darwinism

Since the publication of Origin, a wide variety of opinions had been put forward on whether or not the theory had implications towards human society. One of these which would later be known as Social Darwinism, had been put forward by Herbert Spencer before publication of Origin, and argued that society would naturally sort itself out, and that the more "fit" individuals would rise to positions of higher prominence, while the less "fit" would succumb to poverty and disease. He alleged that government run social programmes and charity would merely hinder the "natural" stratification of the populace, and first introduced the phrase "survival of the fittest".

Related Topics:
Social Darwinism - Herbert Spencer - Survival of the fittest

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Another of these interpretations, later known as eugenics, was put forth by Darwin's cousin, Francis Galton, in 1865 and 1869. Galton argued that just as physical traits were clearly inherited among generations of people, so could be said for mental qualities (genius and talent). Galton argued that social mores needed to change so that heredity was a conscious decision, in order to avoid over-breeding by "less fit" members of society and the under-breeding of the "more fit" ones. In Galton's view, social institutions such as welfare and insane asylums were allowing "inferior" humans to survive and reproduce at levels faster than the more "superior" humans in respectable society, and if corrections were not soon taken, society would be awash with "inferiors." Darwin read his cousin's work with interest, and devoted sections of Descent of Man to discussion of Galton's theories. Neither Galton nor Darwin, though, advocated any eugenic policies such as those which would be undertaken in the early 20th century, as government coercion of any form was very much against their political opinions.

Related Topics:
Eugenics - Francis Galton - 1865 - 1869 - Welfare - Insane asylums

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Apparently non-adaptive features

In Darwin's view, anything that could be expected to have some adaptive feature could be explained easily with his theory of natural selection. In Origin, Darwin had admitted that to use natural selection to explain something as complicated as a human eye, "with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration" might at first appear "absurd in the highest possible degree," but nevertheless, if "numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist", then it seemed quite possible to account for within his theory.

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More difficult for Darwin were highly evolved and complicated features which conveyed apparently no adaptive advantage to the organism in question. He once wrote to a colleague that "The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!" Why should a bird like the peacock develop such an elaborate tail, which seemed to at best be a hinderance in its "struggle for existence"? To answer the question, Darwin developed the theory of sexual selection, which outlined how different characters could be selected for if they conveyed a reproductive advantage to the individual. In Darwin's version of the theory, male animals in particular received the benefits of sexual selection, either by acquiring "weapons" with which to fight over females with other males, or by acquiring beautiful plumage with which to woo the female animals. Much of Descent is devoted to providing evidence for sexual selection in nature, which he also ties in to the development of aesthetic instincts in human beings, as well as the differences in coloration between the human races.

Related Topics:
Peacock - Sexual selection

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Darwin had developed his ideas about sexual selection for this reason since at least the 1850s, and had originally intended to include a long section on the theory in his large, unpublished book on species. When it came to writing Origin, though (his "abstract" of the larger book), he did not feel he had sufficient space to engage in sexual selection to any strong degree, and included only three paragraphs devoted to the subject. Darwin considered sexual selection to be as much of a theoretical contribution of his as was his natural selection, and the vast majority of Descent is devoted exclusively to this topic.

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