PARADOX OF PERAMORPHIC PEDOMORPHOSIS - HETEROCHRONY AND HUMAN-EVOLUTION

This paper reviews Gould's clock model for heterochronic processes and uses that model to develop simple matrix representations of growth an d shape change. Matrix representations of growth and development provi de a common formulation for all heterochronic processes. In particular , we show how neoteny can be diagnosed using such a matrix approach. T he literature is rife with contradictory representations of how neoten y affects growth allometries and the timing of developmental events, a nd therefore of the role of neoteny in human evolution. Through the us e of multivariate models, we explore these relationships and the inter nal consistency of opposing views. Gould's neoteny hypothesis for huma n evolution has been criticized for a number of reasons. Humans do not grow slowly. The slopes of our growth allometries show no common patt ern of change vis-a-vis those of our closest relatives. Humans prolong rather than reduce rates of growth and development of body parts; the brain, for example, ceases growing later in humans than in apes, but during this prolonged period of early ontogeny, it grows at a rapid pa ce. This paper evaluates Gould's hypothesis and its critiques by focus ing on particular questions. Does neoteny imply slow growth? Does it i mply a unidirectional change in the rates of growth of traits? Under n eoteny, should the brain cease growing in ancestor and descendant at t he same age? Does prolongation of phases of growth and development con fute neoteny? On the other hand, is paedomorphosis an inevitable conse quence of prolonged growth and development? We show that, for all of t hese questions, the answer is no. (C) 1996 Wiley-Liss, Inc.