Human Evolution

In On the Origin of Species, Darwin said very little about humans, but later, in The Descent of Man (1871, revised in 1874/1998a), he made his case that humans are also the product of evolution. Both humans and the great apes, he said, descended from a common, distant primate ancestor.

Of Darwin’s books, the one most directly related to psychology is The Expression of the Emotions in Man and Animals (1872/1998b), in which he argued that human emotions are remnants of animal emotions that had once been necessary for survival. In the distant past, only those organisms capable of such things as biting and clawing survived and reproduced. Somewhat later, perhaps, simply baring of teeth or snarling were enough to discourage an aggressor and, therefore, facilitated survival.

fittest (a term Darwin borrowed from Spencer). For example, if there is a shortage of insects in the environment of finches, only those birds with beaks stout enough to also open nuts will survive and reproduce. In this way, as long as other food remains scarce, finches with thinner beaks will tend to become extinct. Thus, a natural selection occurs among the offspring of a species. This natural selection of adaptive characteristics from the individual differences occurring among offspring accounts for the slow transmutation of a species over the eons. Evolution, then, results from the natural selection of those accidental variations among members of a species that prove to have survival value.