It's generally accepted that humans originated in Africa and gradually spread out across the globe from there, but a pair of new studies may paint a different picture. By examining fossils of early hominins, researchers have found that humans and chimpanzees may have split from their last common ancestor earlier than previously thought, and this important event may have happened in the ancient savannahs of Europe, not Africa.

The split between humans and our closest living relatives, chimpanzees, is a murky area in our history. While the point of original divergence is thought to have been between 5 and 7 million years ago, it wasn't a clean break, and cross breeding and hybridization may have continued until as recently as 4 million years ago.

Where the divergence took place is contentious as well, but Eastern Africa is the accepted birthplace of the earliest pre-humans. One of the best candidates for the last common ancestor is Sahelanthropus, known from a skull found in Central Africa dating back to around 7 million years ago. But according to the new studies, bones found in Greece and Bulgaria appear to belong to a hominin that's a few hundred thousand years older.

"Our discovery outlines a new scenario for the beginning of human history – the findings allow us to move the human-chimpanzee split into the Mediterranean area," says David Begun, co-author of one of the studies. "These research findings call into question one of the most dogmatic assertions in paleoanthropology since Charles Darwin, which is that the human lineage originated in Africa. It is critical to know where the human lineage arose so that we can reconstruct the circumstances leading to our divergence from the common ancestor we share with chimpanzees."

The Mediterranean bones are from a species called Graecopithecus freybergi, and it's one of the least understood European apes. The researchers scanned a jawbone found in Greece and an upper premolar from Bulgaria, and found the roots of the teeth to be largely fused together, indicating that the species might have been an early hominin.

"While great apes typically have two or three separate and diverging roots, the roots of Graecopithecus converge and are partially fused – a feature that is characteristic of modern humans, early humans and several pre-humans including Ardipithecus and Australopithecus," says Madelaine Böhme, co-lead investigator on the project.

To get a clearer picture, the researchers studied the sediment that the fossils were found in, and discovered that the two sites were very similar. Not only were they almost exactly the same age – 7.24 and 7.175 million years – but both areas were dry, grassy savannahs at the time, making them prime conditions for hominins.

The researchers found grains of dust that appeared to have blown up from the Sahara desert, which was forming around the same time. This might have contributed to the savannah-like conditions in Europe, and these environmental changes may have driven the two species to evolve differently.

"The incipient formation of a desert in North Africa more than seven million years ago and the spread of savannahs in Southern Europe may have played a central role in the splitting of the human and chimpanzee lineages," says Böhme.

But inferring information from fossils always leaves room for error, and as New Scientist reports, there are researchers who aren't convinced such big claims can be projected from such small features of the fossils. Still, it's an interesting theory, and one that will warrant more study.

The research was published in two separate studies in PLOS ONE.

Source: University of Toronto

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