In this book, Jos Verhulst expands on the evolutionary theory first proposed by Louis Bolk. The theory is based on the premise that aspects of the individual creatures' development -- from juveniles to adults -- are also at work in animal evolution as a whole.

Verhulst shows that, unlike other primates -- who start out with a rather humanlike form but become, say, apes -- humans retain their original fetal form. Standing Darwinism on its head, he argues that humans have not descended from apes, but rather that apes have evolved by diverging from a humanlike prototype.

He also proposes that the gradually emerging human prototype is the driving force, and central trunk, of the evolutionary tree -- the wellspring from which the animal world has sprung.