Thursday, 8 June 2017

Morocco Mystery Man

A composite reconstruction of what its discovers believe is the the earliest known Homo sapien fossil (from Jebel Irhoud), based on scans of multiple specimens. The virtual imprint of the braincase (blue) indicates that brain shape, and possibly brain function, evolved within the Homo sapien lineage, the scientists say.

Credit: Philipp Gunz, MPI EVA Leipzig
The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age : Nature : Nature Research

The press are having one of those, "The textbooks are going to have to be rewritten" days.

Apparently, the textbooks are not just updated with the most recent findings and understanding when a new edition is published; they have to be rewritten because everything we thought we knew was wrong. You sometimes wonder if the science news is written by creationists - except of course that the news media don't then make the absurdly childish leap of concluding that because one little bit of science has been revised this proves the entire body of science is wrong - about everything, so God did it!

But, in this case, the entire evolutionary story of humans now needs to be rewritten, so we are told. You might now be wondering what is this amazing discovery? Humans are not apes? Not African apes, maybe? We've evolved from guinea pigs or spontaneously generated? The truth is slightly more prosaic of course, in fact it barely rates as startling at all - interesting and thought-provoking, naturally, but startling? The 'startling' fact is some archaic human fossil remains including skulls, flint tools and animal remains found in Morocco have been dated to about 300,000 years old and may be the oldest fossil Homo sapiens so far discovered.

The timing and location of the emergence of our species and of associated behavioural changes are crucial for our understanding of human evolution. The earliest fossil attributed to a modern form of Homo sapiens comes from eastern Africa and is approximately 195 thousand years old1, 2, therefore the emergence of modern human biology is commonly placed at around 200 thousand years ago3, 4. The earliest Middle Stone Age assemblages come from eastern and southern Africa but date much earlier5, 6, 7. Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of H. sapiens8. A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible. These ages are also consistent with the faunal and microfaunal9 assemblages and almost double the previous age estimates for the lower part of the deposits10, 11. The north African site of Jebel Irhoud contains one of the earliest directly dated Middle Stone Age assemblages, and its associated human remains are the oldest reported for H. sapiens. The emergence of our species and of the Middle Stone Age appear to be close in time, and these data suggest a larger scale, potentially pan-African, origin for both.

So what exactly is new here?

Well, we previously thought that modern humans, H. sapiens, emerged as a distinct species around 200,000 years ago in East Africa (with South Africa flagged as a possibility), so this puts the date back by about 100,000 years. It also shows that H. sapiens may have been widespread in Africa and was present at least in the far North West, north of the Sahara.

The animal remains found with them show they had a diet of big game such as gazelle and zebra - which also begs the question, what were sub-Saharan species doing in Morocco? The answer to that is also the answer to the question of how humans from East and maybe South Africa came to be north of the Sahara. The answer could well be the so-called Sahara Pump. I mentioned this in my recent book, What Makes You So Special? The idea is based on the archaeological evidence that North Africa experienced a slow cycle of very wet weather alternating with very dry weather. During the wet period the Sahara became savanna with lakes and rivers and contiguous with the sub-Saharan savanna enabling sub-Saharan species to migrate north along, in this case, maybe with humans. In the dry periods the Sahara dried up isolating populations in the north.

But we know that H. erectus had made it out of Africa well before this period and would almost certainly have been in North Africa. It had made it into South East Asia before this time, so migrating along the southern Mediterranean coast from the Nile Delta would have been the more remarkable it it hadn't happened, even assuming the Nile was the route taken out of Africa.

Looking at the published images of the composite skull, made from several fragments from different individuals, there are some obvious archaic features. Not only is the cranial capacity smaller than that of modern humans but there is a pronounced brow-ridge, a receding chin and a prognathic maxilla reminiscent of H. erectus and H. neanderthalensis. Additionally, the H. erectus skulls found at Dmanisi in Georgia show such a range of features that it has prompted some authorities to suggest that H. erectus was a very variable species. It was also very widespread species so local variants would be very likely.

It seems very likely therefore that the Moroccan fossils are from an archaic pre-modern Homo. Where exactly it comes between H. erectus and H. sapiens, if in fact it does and isn't an evolutionary dead-end like H. neanderthalensis, is the question. As always with an evolving species, exactly where to draw the line between one species and an immediate predecessor s always going to be arbitrary because there never was such a line in reality. This becomes especially difficult if the species is widespread and evolving differently in different parts of its range.

What is emerging is a picture of a widespread archaic Homo gradually evolving over a wide range which could have included Eurasia, diverging into local populations and sometimes coming into contact with other populations, sharing genes and technology. One of these populations eventually emerged as H. sapiens to spread worldwide to become the predominant form, still carrying archaic genes, more so in some populations than others.

The joke on those creationists who will undoubtedly be jumping for joy at the thought that 'science has got it all wrong and is having to rewrite the text books yet again", is that finds of intermediate forms such as this entirely refute their claims that there are no such thing and nothing preceded modern humans because we never evolved. Not only are there now dozens of these transitional forms but there are so many they are confusing the picture rather than clarifying it. They leave no doubt at all though that the human story is an evolutionary one and that modern humans emerged from African apes via archaic hominids.

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