Charles Darwin closed his On the Origin of Species (1859) with a provocative promise that ‘light will be thrown on the origin of man and his history’. In his later books The Descent of Man (1871) and The Expression of Emotions in Man and Animals (1872), Darwin shed some of that promised light, especially on the evolved emotional and cognitive capacities that humans shared with other mammals.
In one scandalous passage, he demonstrated that four ‘defining’ characteristics of Homo sapiens—tool use, language, aesthetic sensitivity and religion—are all present, if rudimentary, in nonhuman animals. Even morality, he argued, arose through natural selection. Altruistic self-sacrifice might not give the individual a survival advantage, but, he wrote:
“There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection.”
Yet Darwin’s revolutionary understanding of the evolved nature of human emotions has been neglected since. When scientists turned again to the mind a century later, the computer was the model that both sparked the cognitive sciences revolution and served as its exclusive investigative tool. The computational model of the mind has been very powerful, but it has no way (and no need) to capture the biological ingredient of motivational feeling-states, and has been unconcerned with the evolved substrate to such processes. Even when evolutionary psychology rose to prominence in the 1990s, it did so by ignoring the actual evolved physiology and behavior of brain and body. Rather, it set out on a search for computational modules that had placed human behavior in some largely mythical Pleistocene. Indeed, contemporary moral psychology and its philosophical counterpart often continue this modular approach, assuming the existence of innate normative switches in the human mind and discounting the emotional nature of ethical actions.