Introduction

Evolution modifies the developmental pattern and thus understanding the evolution of development is critical to identifying how and when the presumed descendant morphological patterns, such as our own, originated. Likewise, understanding how and when these patterns changed ultimately assists in answering why they changed; that is, what evolutionary problems and solutions they reflect. Here we address two aspects of ontogeny in Homo erectus in order to define developmental shifts that have characterized later human evolution. First, we undertake a preliminary heterochronic comparative analysis of cranial ontogeny in H. erectus and H. sapiens. This investigation focuses on alterations in the relations between size, shape, and age at maturation between ancestral and descendant species. Heterochronic transformations can thus be taken to refer, rather narrowly, to shifts in allometric or relative growth trajectories between an ancestor and a descendant species. Using this approach requires both juvenile and adult fossils, although it does not require knowledge of the specific developmental age of each juvenile fossil (Shea, 2000). Second we explore differences in how these taxa grew to reach adult size, with special emphasis on whether or not a growth spurt characterized H. erectus. This component of the research investigates the possibility that growth in H. erectus, like that in H. sapiens, was subdivided into relatively discrete time periods, including a period prior to an adolescent growth spurt and a period after the initiation of the growth spurt.