Patterns of Neoteny in the relative skull growth in Homo and Pan

    Succesive stages of skull development from infancy to maturity in chimpanzees (top three) and humans (bottom pair). Infants of both species have a large craniums and small faces. Relatively more rapid growth of the jaw in juvenile chimps (above, middle) gives them skull proportions resembling those of adult humans, in which the relative proportions are less altered (right). Continued rapid expansion of the jaw in adult apes (top right & below right) gives them proportionately larger jaws and smaller crania.

    The two photographs of a juvenile and adult male chimpanzee are from a 1926 study by the German anthropologist Adolf Naef. Of the former, he says,"[It] is the the most human-like picture of an animal, of any that is known to me."