Human artifacts recently discovered in the United Arab Emirates date back at least 100,000 years, which means our ancestors might have left Africa up to 125,000 years ago…twice as long ago as previously thought. What’s going on here?
The tools discovered during an excavation in the U.A.E., located in the southeastern part of the Arabian peninsula, have been reliably dated to 100,000 years ago. Genetic evidence has suggested modern humans did not leave Africa until about 60,000 years ago, but these tools appear to be the work of our ancestors and not other hominids like Neanderthals.
If they are the work of our ancestors, then they’ve been found outside Africa at least 40,000 years ahead of schedule. But, as the paleontologists behind this discovery are quick to point out, the 60,000 year figure is one based on only one strand of evidence, and that’s genetic data. It’s a useful tool, to be sure, but using genetics to reconstruct a species’s history can be tricky - genetic data once said domestic dogs were 120,000 years old, but more recent evidence has shown they’re actually much closer to 20,000 instead.
This find is one of the first major archaeological discoveries that seems to place anatomically modern humans out of Africa - but, helpfully, still close to Africa, so it’s a bit easier to reconstruct their path and timing of migration. That automatically makes this an intriguing find, although we can’t instantly dismiss the old 60,000 years figure. This is an extraordinary claim and, as one of the best scientific maxims points out, it requires extraordinary evidence.
Well, I can’t guarantee their evidence is sufficiently extraordinary, but at a press conference yesterday the researchers involved did lay out some compelling reasons to believe the basics of the find - that modern humans lived in Arabia 100,000 years ago - even if they were reluctant to discuss the wider implications.
They answered a number of questions one might have about this discovery, so let’s dive in:
How do we know anatomically modern humans made these tools?
Paleontologist Tony Marks explains how they identified the likely makers of these tools, which were classified assemblage C:
“There were two possibilities for assemblage C. First, that it was made by local people who’d been there for a long time and who would have left similar artifacts around the landscape. Or second, it was made by people moving into the area. Since assemblage C was 120,000 years old, we looked at what was in southeastern Arabia at that time, there was literally nothing. Long before 120,000 in western Arabia there was what we call the Acheulean, but it had disappeared about a half million years ago, leaving a 400,000 year gap between it and assemblage C. Thus it seemed that assemblage C was made by people coming from somewhere outside southern Arabia, either from the north or from the west.
“A comparison of contemporaneous Paleolithic assemblages from the north showed they totally lacked the bifacial tool production found at assemblage C. Their technique was quite different. Thus, they were unrelated. In east Africa, however, there were contemporaneous Paleolithic assemblages that not only used bifacial techniques to make some of their tools, but also used the other two techniques, blade production and radial (levaloir). An origin in east Africa for assemblage C people therefore was most plausible based on the stone tools and how they were made.”
But couldn’t it have been another hominid species that had already left Africa, such as the Neanderthals?
Marks offers some logical reason why Neanderthals are very unlikely candidates to be behind these tools, even leaving aside the fact that the tools fit the more human style:
We can look at it from a broad point of view. If these tools were not made by modern man, who might have made them? Well, could Neanderthals have made them? Well, at 120,000 years ago, beginning of the inter glacial, Neanderthals had pretty well developed their facial characteristics and body characteristics to be recognizable as Neanderthals and not the yet classic Neanderthals. But they’re mainly in Europe at about the beginning of the last interglacial there’s a movement, a spread of Neanderthals along the temperate zone to the east. That is the Crimea, southern Russian plain out to central Asia. There is no evidence for any Neanderthals south of that temperate zone to the east. It is only in OSI4, that is when it starts getting cold that you have movements of Neanderthals out of the highlands of the temperate zones down into the (levant). Into lower elevations where the environment is better. Here is a group of Neanderthals who instead of going into this temperate zone, which was getting better, they took a turn south, went several thousand kilometers into what at the time was desert, really dry areas, until they reached southern Arabia, which happened to be very good because of monsoons that were coming up from the south. It seems to me a very difficult explanation and one that is – doesn’t follow any reasonable logic.
If these tools date back to 100,000 years, why then do they think humans left Africa 125,000 years ago?
Adrian Parker explains how ancient climate limited the times when humans could leave Africa, and that about 125,000 years ago was an ideal time to move into Arabia:
We need to go back to where modern humans emerged in east Africa. This occurred approximately 200,000 years ago. The period between 200,000 years ago until 130,000 years ago corresponds to time when there was a global ice age. During ice ages global sea levels fall as water becomes locked up in the vast ice sheets in the northern and southern hemispheres. When ice ages occur, the world’s major desert belts also expand and thus modern humans would have been restricted to east Africa as the deserts of the Sahara and Arabia posed major geographical barriers that prevented movement out of the region.
Read more at io9.com
By 130,000 years ago global climatic conditions changed and we moved into an interglacial, a period of warmer, global temperatures. At this time, the Indian Ocean monsoon system was forced northwards, bringing rainfall into Arabia. The previously arid interior of Arabia would have been transformed into a landscape covered largely in savannah grasses with extensive lakes and river systems. At the onset of the inter glacial, sea levels in the southern Red Sea were over 100 meters lower than today. this led to a brief window of time when sea levels were still low and Arabia experienced a wetter climate, thus humans would have been able to cross a much narrower Red Sea, perhaps as little as four kilometers wide before sea levels rose sufficiently to make the crossing more difficult.”
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