Guided by modern evolutionary theory, scientists have been able to explicate the origin of the morphology of the human body. However, the evolution of the human mind has yet to be so satisfactorily accounted for. Comparative psychology has already succeeded in providing evidence to help clarify the biobehavioral origins of human language and symbolic competence through studies of our nearest living relatives—the Pongidae (chimpanzee, Pan ; orangutan, Pongo ; and gorilla, Gorilla). These great apes are substantially more like humans than are the lesser apes, monkeys, or any other mammals. The similarities between human and chimpanzee DNA exceed 98 percent. Genetic relatedness enhances the probability that life forms will have similar psychology as well as appearance. Consequently, we might reasonably expect to find linguistic and cognitive competencies in the ape that are similar to those observed in humans.

Early Studies

Speculation that apes might...