Charles Darwin: The Descent of Man

Explanation and Analysis of the Document

In chapter XXI, Darwin offers a summary and conclusion of The Descent of Man. His chief conclusion is that “man is descended from some less highly organised form,” a conclusion he reaches by seeing natural phenomena as connected. One thing leads to another, and the direction of development tends to be toward greater organization, which proceeds in small steps by slight variation. The source of variation lies more in the constitution of the organism than in the surrounding conditions in which the organism develops. And the process, in humans as in other organisms, appears to be one in which individuals better fitted to their environment survive in greater numbers than those less well fitted.

When Darwin turns to the development of intellect, he is especially attentive to language: “As soon as the half-art and half-instinct of language came into use,” its action on the brain became one factor in the brain's further development. With regard to moral qualities, their foundation “lies in the social instincts, including under this term the family ties.” According to Darwin, a moral being “is capable of reflecting on his past actions and their motives—of approving of some and disapproving of others.” The fact that humans are the only “moral” beings is the greatest distinction between humans and “lower” animals. Humans cannot avoid “looking both backwards and forwards, and comparing past impressions,” a fact that Darwin connects with the structure of the human brain. He links “the moral faculties” with the mental activity that vividly recalls past impressions. He associates this in turn with imagination and says that “whatever renders the imagination more vivid and strengthens the habit of recalling and comparing past impressions, will make the conscience more sensitive.” Social animals are motivated partly by “a wish to aid the members of their community in a general manner.”

Anticipating criticism of this work as “irreligious,” Darwin challenges critics to show why it is more irreligious to account for the origin of the human species as development from a lower form by way of variation and natural selection than to explain the birth of the human individual as the result of ordinary reproduction. The birth of the individual and that of the species are both parts of a grand sequence of events, not “blind chance.”

Darwin distinguishes sexual selection from natural selection. Sexual selection depends on the success of some individuals over others of the same sex, while natural selection depends on the success of both sexes “in relation to the general conditions of life.” Admitting the principle of sexual selection leads to the conclusion that “the nervous system not only regulates most of the existing functions of the body, but has indirectly influenced the progressive development of various bodily structures and of certain mental qualities.” This leads Darwin to suggest that human beings should give as much attention to their marriages as they do to the breeding of animals. He advocates conscious intervention in the process of natural selection on the basis of moral judgment, a position that led some thinkers to advocate eugenics (the process of improving the human race by controlling breeding). Darwin concludes by saying that he would “as soon be descended from that heroic little monkey, who braved his dreaded enemy in order to save the life of his keeper . . . as from a savage who delights to torture his enemies, offers up bloody sacrifices, practices infanticide without remorse, treats his wives like slaves, knows no decency, and is haunted by the grossest superstitions.”