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21 October 2013
Skull find rebuts multiple human species idea

Paleoanthropologists from the University of Zurich have uncovered the intact skull of an early Homo individual in Dmanisi, Georgia. This find is forcing a change in perspective in the field of paleoanthropology: human species diversity two million years ago was much smaller than presumed thus far. However, diversity within the 'Homo erectus,' the first global species of human, was as great as in humans today.
     The skull has the largest face, the most massively built jaw and teeth and the smallest brain within the Dmanisi group. It is the fifth skull to be discovered at the site. Previously, four equally well-preserved hominid skulls as well as some skeletal parts had been found there. Taken as a whole, the finds show that the first representatives of the genus Homo began to expand from Africa through Eurasia as far back as 1.85 million years ago.
     Because the skull is completely intact, it can provide answers to various questions which up until now had offered broad scope for speculation. According to Christoph Zollikofer, anthropologist at the University of Zurich,, the reason why Skull 5 is so important is that it unites features that have been used previously as an argument for defining different African "species." In other words: "Had the braincase and the face of the Dmanisi sample been found as separate fossils, they very probably would have been attributed to two different species."
     Marcia Ponce de León, who is also an anthropologist at the University of Zurich, adds: "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. Zollikofer 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."
     The present findings are supported by an additional study recently published in the PNAS journal. In that study, Ponce de León, Zollikofer and further colleagues show that differences in jaw morphology between the Dmanisi individuals are mostly due to differences in dental wear. 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, where it is first documented from about 1.2 million years ago.
     Other palaeoanthropologists, however, believe that at least three distinct species of humans co-existed in Africa. They include Fred Spoor from University College London. He said that the methods of analysis that the team used were not sufficient to infer that these fossils were the same species. Comparing diversity patterns in Africa, Eurasia and East Asia provides clues on the population biology of this first global human species.

Edited from ScienceDaily, BBC News (17 October 2013)

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