Unique skull sheds new light on human evolution

Washington – A new skull, found in Dmanisi, suggests that nearly half a dozen species of our early human ancestor may have been all Homo erectus.

The skull found by anthropologists from the University of Zurich as part of a collaboration with colleagues in Georgia funded by the Swiss National Science Foundation, has the largest face, the most massively built jaw and teeth and the smallest brain within the Dmanisi group.

Previously, four equally well-preserved hominid skulls as well as some skeletal parts had been found there.

Marcia Ponce de Leon, who is also an anthropologist at the University of Zurich, points out another reason: paleoanthropologists often tacitly assumed that the fossil they had just found was representative for the species, i.e. that it aptly demonstrated the characteristics of the species.

Statistically this is not very likely, she says, but nevertheless there were researchers who proposed up to five contemporary species of early Homo in Africa, including Homo habilis, Homo rudolfensis, Homo ergaster and Homo erectus.

Ponce de Leon said that it is also decisive that we have five well-preserved individuals in Dmanisi whom we know to have lived in the same place and at the same time.

These unique circumstances of the find make it possible to compare variation in Dmanisi with variation in modern human and chimpanzee populations. Christoph Zollikofer, anthropologist at the University of Zurich, summarizes the result of the statistical analyses as follows: Firstly, the Dmanisi individuals all belong to a population of a single early Homo species. Secondly, the five Dmanisi individuals are conspicuously different from each other, but not more different than any five modern human individuals, or five chimpanzee individuals from a given population.

This shows the need for a change in perspective: the African fossils from around 1.8 million years ago likely represent representatives from one and the same species, best described as Homo erectus.

This would suggest that Homo erectus evolved about 2 million years ago in Africa, and soon expanded through Eurasia – via places such as Dmanisi – as far as China and Java.