Belgian scientist Jos Verhulst presents the most thorough research to date elaborating an evolutionary theory first set forth by Dutch anatomist Louis Bolk in the early twentieth century. This theory is based on the proposition that dynamic principles inherent in the development of individual organisms are also at work in animal evolution as a whole. A chimpanzee fetus, for example, is strikingly similar to its human counterpart: its cranium is rounded, its face flat, and its hair is restricted to its head. As it develops, however, the chimp diverges from its original, humanlike form, assuming specialized apelike features.
In this detailed comparative study of numerous organs, Verhulst shows that, unlike the other primates, humans retain their original juvenile form. Standing Darwin on his head, he concludes that humans did not descend from apes; rather, apes evolved by diverging from a humanlike prototype. He also shows that our human tendency to retain our fetal form (fetalization, or retardation) is complemented by further development (hypermorphosis) of such organs as the legs, heels, forebrain, and larynx through which we attain our eminently human capacities of upright posture, thinking, and speech.