Homo Erectus - Classification and Special Distinction

Classification and Special Distinction

Many paleoanthropologists still debate the definition of H. erectus and H. ergaster as separate species. Several scholars suggested dropping the taxon Homo erectus and instead equating H. erectus with the archaic H. sapiens. Some call H. ergaster the direct African ancestor of H. erectus, proposing that it emigrated out of Africa and immigrated to Asia, branching into a distinct species. Most dispense with the species name ergaster, making no distinction between such fossils as the Turkana Boy and Peking Man. Although "Homo ergaster" has gained some acceptance as a valid taxon, these two are still usually defined as distinct African and Asian populations of the larger species H. erectus.

While some have argued (and insisted) that Ernst Mayr's biological species definition cannot be used here to test the above hypotheses, one can, however, examine the amount of morphological cranial variation within known H. erectus / H. ergaster specimens, and compare it to what one sees in disparate extant groups of primates with similar geographical distribution or close evolutionary relationship. Thus, if the amount of variation between H. erectus and H. ergaster is greater than what one sees within a species of, say, macaques, then H. erectus and H. ergaster may be considered two different species.

The extant model of comparison is very important, and selecting appropriate species can be difficult. (For example, the morphological variation among the global population of H. sapiens is small, and our own special diversity may not be a trustworthy comparison). As an example, fossils found in Dmanisi in the Republic of Georgia were originally described as belonging to another closely related species, Homo georgicus, but subsequent examples showed their variation to be within the range of Homo erectus, and they are now classified as Homo erectus georgicus.

H. erectus had a cranial capacity greater than that of Homo habilis (although the Dmanisi specimens have distinctively small crania): the earliest remains show a cranial capacity of 850 cm³, while the latest Javan specimens measure up to 1100 cm³, overlapping that of H. sapiens.; the frontal bone is less sloped and the dental arcade smaller than the australopithecines'; the face is more orthognatic (less protrusive) than either the australopithecines' or H. habilis's, with large brow-ridges and less prominent zygomata (cheekbones). These early hominins stood about 1.79 m (5 ft 10 in), (Only 17 percent of modern male humans are taller) and were extraordinarily slender, with long arms and legs.

The sexual dimorphism between males and females was slightly greater than seen in H. sapiens, with males being about 25% larger than females. However, their dimorphism is drastically lesser than that of the earlier Australopithecus genus. The discovery of the skeleton KNM-WT 15000, "Turkana boy" (Homo ergaster), made near Lake Turkana, Kenya by Richard Leakey and Kamoya Kimeu in 1984, is one of the most complete hominid-skeletons discovered, and has contributed greatly to the interpretation of human physiological evolution.

For the remainder of this article, the name Homo erectus will be used to describe a distinct species for the convenience of continuity.