Fair-ish and Balanced-ish
Tuesday, January 27, 2004
Out of Africa or Out of Everywhere
Human evolution is one of the most interesting aspects of modern biology, and one current controversy is where modern humans come from. There are two main schools of thought, one teaches that modern humans originated in Africa and spread over the globe, replacing other archaic human populations. The other school of thought, puts forward the case for the archaic human populations evolving into modern humans. In the very amateurish opinion of the author of this blog, the evidence tends to point towards the out of Africa hypothesis being correct.
A recent paper, published in the Proceedings of the National Academy of Sciences by Katerina Harvati, Stephen Frost and Kieran McNulty (February 3, 2004 vol. 101 no. 5 page 1149) has looked into the relationship between Neanderthals and humans.
The authors have examined the shapes of skulls of a number of primates, including modern humans (from a range of different regions), Neanderthals, some archaic humans, Old world Monkeys, and African Apes.
15 different points of the skulls where measured, and from this, a feature known as the Mahalanobis distance was determined. The Mahalanobis distances could then be used to quantitatively compare skulls.
If the out of Africa hypothesis is correct, one wouldn't expect Neanderthals to be similar to any particular human skull. This is because, the Neanderthals were replaced by a group of H. Sapiens who evolved in Africa and then spread North into Europe (and other parts of globe) displacing them.
On the other hand, if the regional continuity model is correct, the Neanderthal skulls should be closer to some human groups (who had larger genetic input from the Neanderthals) than other human groups (who didn't originate in Europe, and thus have smaller genetic input from the Neanderthals).
The results of the study support the first hypothesis. Neanderthal skulls show no statistical significant similarity to one human group over other. As the authors conclude:
The specific status of Neanderthals is important beyond taxonomic considerations due to its implications for modern human origins. Under the regional continuity model, Neanderthals are considered to be a subspecies of H. sapiens that contributed to the ancestry of at least the early modern Europeans. On the other hand, the recognition of Neanderthals as a species distinct from, but sympatric with, early modern humans strongly implies that they were not ancestral to any extant human populations, even if limited interbreeding occurred. The extreme morphological difference between Neanderthals and modern humans relative to subspecific differences among other catarrhines is not consistent with their subspecific designation, as postulated by the regional continuity model. Moreover, Neanderthal ancestry for the sympatric and roughly synchronic early modern Europeans is also refuted: the morphological distance found between these two fossil groups was equivalent to those between Neanderthals and other modern human populations. We interpret the evidence presented here as supporting the view that Neanderthals represent an extinct human species and therefore refute the regional continuity model for Europe.