Humans
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All present-day non-African populations are descended from a single wave of humans who left the ancestral continent between 70,000 and 50,000 years ago before spreading across the world. However, archaeological evidence suggests that some human groups may have expanded out of Africa much earlier than this, yet somehow failed to become established or leave any lasting genetic legacy. Now, we may finally know why.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.By analyzing four prehistoric sites in Dhofar, Oman, the authors of a new study - which has yet to be peer-reviewed - found this part of the Arabian peninsula was home to Homo sapiens between 109,000 and 95,000 years ago. These ancient humans left behind tools associated with the Nubian Levallois technology, which first emerged in the Nile Valley of northeast Africa around 150,000 years ago.
Given that the Bab al Mandab strait - which connects Africa to Arabia - reduced in width from 30 kilometers to just 5 kilometers around 115,000 years ago when sea levels dropped, the researchers suspect that this pioneering community may have taken advantage of this opportunity to hop across the water. Upon arrival, they would have discovered a humid, grass-covered landscape that could have provided them with everything they needed.
For example, the study authors found evidence of vast lakes around 100,000 years ago, while the active growth of stalagmites and stalactites during this period indicates that significant dripwater systems were flowing through local caves.
However, around 93,000 years ago, the Nubian Levallois tools suddenly stopped appearing in the archaeological record. Later artefacts, representing the Mudayyan industry, show no continuity with this earlier technology, indicating that the makers of the Nubian tools probably disappeared completely.
Palaeoclimate data suggests that their exit coincided with a period of drastic aridification and environmental collapse as the landscape rapidly dried out. “Groundwater-fed springs once sustained by aquifer recharge were reduced to desiccated basins,” explain the researchers.
“These results demonstrate that early human expansions beyond Africa were climate-dependent and demographically fragile, and that the global establishment of our species was preceded by repeated failures,” they write.
Interestingly, however, Nubian Levallois artifacts in the eastern Mediterranean region are roughly the same age as those in Oman, suggesting two related groups of humans may have left Africa at around the same time. One of these populations followed a southern route into Arabia, where they ultimately perished without crossing paths with Neanderthals or any of the other hominins that occupied Eurasia during this period.
The other, however, headed slightly further north into the Middle East, where they may well have encountered - and potentially mated with - Neanderthals. Exactly what became of this group is unclear, although we do know that they didn’t make it either, as none of their genes were passed on to more recent humans.
“These findings add to a growing body of genomic evidence that the successful colonisation of Eurasia occurred after 80 [thousand years ago],” write the researchers. “Earlier dispersals were demographically fragile and did not establish an enduring foothold outside Africa.”
A preprint of the study is currently available on Research Square.
