MULTIPHASIC GROWTH-MODELS AND THE EVOLUTION OF PROLONGED GROWTH EXEMPLIFIED BY HUMAN BRAIN EVOLUTION

New models for multiphasic growth are presented. They are illustrated by analysis of brain growth in humans and chimpanzees, and the results are used to test the hypothesis of evolution by proportional growth p rolongation: that all descendant growth phases are extended by the sam e factor while each remains at the ancestral growth rate. The results are consistent with the hypothesis and imply that gross brain weight i ncrease towards humans required change in only one growth parameter: p rolongation of the nonlinear ancestral growth phases. The restricted a nd orderly nature of the developmental change hints at a basis in few genetic changes. Proportional growth prolongation is of general evolut ionary importance because it can reorganize body proportions. (C) 1998 Academic Press Limited.