CORONADO, CALIFORNIA – Most people do not think of Charles Darwin as a psychologist. In fact, his work revolutionized the field. Before Darwin, philosophical speculation shaped our psychological understanding. But even great philosophers – Plato, Aristotle, Hobbes, Hume, Locke, Kant, Schopenhauer, Nietzsche, and others – could only describe current mental events and behaviors; they could not explain their causes.
Darwin provided the profound understanding that evolution has influenced the shape of our minds as strongly as it has the shape of our bodies. Since humans evolved from the same primate ancestor as modern chimpanzees or gorillas, he suggested one could learn more by comparing human instincts, emotions, and behaviors to those of animals than one can surmise from subjective speculation. As he put it, “he who understands baboon would do more towards metaphysics than Locke.”
Philosophy is inadequate to understand the roots of human psychology, because self-reflection does not make us aware of the forces that drive most of our reactions to the environment. Rather, we are subject to inborn tendencies, which develop through the reciprocally influential forces of natural and sexual selection.
Natural selection is the process by which the variants within a species that are best adapted to survive in their environment win the reproductive contest – at least until an even better-adapted variant comes along. The traits that enable people to feed and protect themselves increase the likelihood that they will live long enough to produce offspring, whom they will be able to feed and protect until maturity.
In a sense, sexual selection is the psychological extension of natural selection. But, instead of gaining an advantage from traits that enhance one’s ability to survive, one gains an advantage from qualities that potential mates have evolved to find appealing.
Given that humans’ sexual choices determine who reproduces most and, in turn, which physical and psychological features are favored over time, a trait that may not help a person to survive can still provide a reproductive advantage that is passed along to offspring. In other words, in choosing a mate, one shapes the course of evolution.
Moreover, the principle of sexual selection implies that, in addition to regulating bodily functions, the nervous system indirectly influences the progressive development of bodily and mental structures such as ornamental appendages; cognitive skills like musical ability; and characteristics such as courage and perseverance. Peacocks have evolved to have long, colorful feathers simply because peahens have evolved to find them attractive.
Darwin explained that such qualities are propagated and enhanced over generations, through “the exertion of choice, the influence of love and jealousy, and the appreciation of the beautiful in sound, color, or form.” Indeed, while natural selection is blind, sexual selection has an eye for beauty – although the nature of beauty is always in the eye of the beholder.
Given that human psychology has developed through a sometimes-uneasy balance of natural and sexual selection, evolution and psychology influence and interact with each other. Darwin’s contributions to understanding human psychology involved careful study of child development, which he reported in 1877 in “Biographical Sketch of an Infant.” For the first three years of his first-born son William’s life, Darwin observed him with the practiced eye of a naturalist, recording developments as diverse as his ability to follow a candle with his eyes to the first manifestations of conscience. Darwin also pioneered the experimental tools of scientific psychology, such as the use of photographs of facial expressions and surveys to determine the universality of human emotions.
Darwin had already made most of his major psychological discoveries even before he identified natural selection as the mechanism of evolution – but he waited 35 years before publishing his findings. This decision can be partly attributed to his meticulous approach to research, which entailed carefully collecting and studying evidence before presenting theories.
But Darwin also knew that, if he needed time to accept his own conclusions, the rest of the world was not ready to face such a materialist view of humanity. He shied away from the inevitable confrontation with critics – among whom were friends and colleagues.
By the time Darwin died, his ideas had gained significant influence among psychologists and neuroscientists – even if they did not always fully realize it. Sigmund Freud never met Darwin, but most of his mentors were enthusiastic Darwinists. Just as Isaac Newton revolutionized astronomy and physics by “standing on the shoulders” of his predecessors, Freud built on Darwin’s evolutionary insights in order to understand psychological symptoms, dreams, myths, art, anthropology, and much more. Freud’s biographer, Ernest Jones, was mistaken in calling Freud “the Darwin of the mind.” Darwin himself was the Darwin of the mind; Freud was his great popularizer.
Since Darwin, academic psychology has expanded significantly, enriched by the sophisticated tools of cognitive science, cybernetics, and brain imaging. But most of these developments have been derivative elaborations of Darwin’s grand evolutionary model. The fundamentals of our conception of human nature can all be found in Darwin’s notebooks, written 175 years ago and before his thirtieth birthday.