Habiline variation: a new approach using STET

The problem of whether the hominid fossil sample of habiline specimens is comprised of more than one species has received much attention in paleoanthropology. The core of this debate has critical implications about when and how variation can be explained by taxonomy. In this paper, we examine the problem of whether the observed variation in habiline samples reflects species differences. We test the null hypothesis of no difference by examining the degree of variability in habiline sample in comparison with other single-species early hominid fossil samples from Sterkfontein and Swartkrans (Sterkfontein is earlier than the habiline sample, Swartkrans may be within the habiline time span). We developed a new method for this examination, which we call STandard Error Test of the null hypothesis of no difference (STET). Our sampling statistic is based on the standard error of the slope of regressions between pairs of specimens, relating all of the homologous measurements that each pair shares. We show that the null hypothesis for the habiline sample cannot be rejected. The similarities of specimen pairs within the habiline sample are not more than those observed between the specimens in the australopithecine samples we analyzed.