I fully subscribe to the judgment of those writers who maintain that of all the differences between man and the lower animals, the moral sense or conscience is by far the most important … . It is the most noble of all the attributes of man, leading him without a moment’s hesitation to risk his life for that of a fellow-creature; or after due deliberation, impelled simply by the deep feeling of right or duty, to sacrifice it in some great cause … . The following proposition seems to me in a high degree probable—namely, that any animal whatever, endowed with wellmarked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense or conscience.

—Charles Darwin, The Descent of Man, 1871