Mystery of a West African skull from 13,000 years ago

16 September 2011

Humans with primitive skull features were still living in West Africa 13,000 years ago, much more recently than expected, according to scientists reporting in the PLoS One journal today

An international team of scientists studied human skeletal remains from Iwo Eleru in Nigeria, West Africa, which was unearthed in 1965.

The team was led by Prof Katerina Harvati of the University of Tubingen, Germany and Professor Chris Stringer, human origins expert at the Natural History Museum, and author of the new book The Origin of Our Species.

The skeleton was confirmed as dating to about 13,000 years ago. However, the skull did not look like one from a recent human, particularly those living in West Africa today. Instead, it shared many similarities with African fossil skulls that date to more than 100,000 years ago.

Stringer says that this suggests that fully modern humans in Africa overlapped with more archaic forms during the last 200,000 years (modern humans, Homo sapiens, evolved in Africa around 200,000 years ago). 

'The mixed features of Iwo Eleru may reflect interbreeding between primitive and modern forms of Homo sapiens in that continent.'

Stringer, who first studied the skull 40 years ago, adds, ‘The latest study essentially confirms the research that I carried out on the fossil in 1972, but uses much more sophisticated techniques of study.

‘It shows that the evolution of modern humans in Africa was a more complex process than many of us believed, and that populations of archaic hominins or their genes survived in Africa much later than previously thought.’

Other late surviving humans

Modern humans shared the planet up until recently with other ancient human species. Research in the last few years has shown evidence for the Denisovans in central Asia about 40,000 years ago, and the Flores people in Indonesia as recently as 17,000 years ago.

And the Neanderthals survived up until about 30,000 years ago.

Stringer also mentions a study published last week suggesting that some African populations have genes from an unknown extinct human group, perhaps descendants of the earlier human species Homo heidelbergensis

‘Our research on Iwo Eleru concurs with recent genetic reports of admixture between archaic humans and anatomically modern humans in Africa as recently as 35,000 years before present.’

Who could it belong to?

So how should the Iwo Eleru skull be classified? Stringer says that it is similar to recent humans in having a smaller browridge, and longer frontal and parietal bones. Yet the skull is also long, low and broad across the base. 

‘Its nearest neighbour in the analyses is the Ngaloba (Laetoli 18) skull from Tanzania, thought to be about 140,000 years old, and Iwo Eleru did not resemble any recent African skulls in the analyses we performed. 

'However, I still regard it as a Homo sapiens, albeit one with more ancient features. 

'Remarkably, the Iwo Eleru skeleton is the oldest known so far from the entire West African region, so we hope that new field work can recover other, and older, human fossils from this area. 

'Meanwhile, we intend to study the associated lower jaw and fragmentary skeleton, and make comparisons with similarly-dated fossils from other parts of Africa.'

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