By Chris Stringer, The Natural History Museum London.
Many scientists accept that the human fossils from Omo Kibish and Herto in Ethiopia, dated between about 150-200,000 years ago represent the earliest known members of our species Homo sapiens. However, I now accept that evidence is building from both fossils and DNA that the modern human and Neanderthal lineages separated at least 500,000 years ago. In my view, the date of this divergence should mark the origin of these two groups, with the implication that there should fossils in Africa and Eurasia older than 200,000 years that lie on the respective lineages of modern humans and Neanderthals.
There is good evidence that this is true for the Neanderthals in Europe, since the Sima de los Huesos (‘Pit of the Bones’) fossils from Atapuerca can now be firmly placed on the Neanderthal lineage from both their anatomy and their DNA at around 430,000 years. Although we don’t yet have good ancient DNA evidence from Africa, I have suggested that fossils such as Florisbad (South Africa), Eliye Springs (Kenya) and Jebel Irhoud (Morocco) might well represent early or “archaic” Homo sapiens that existed before the full suite of modern human characteristics had evolved. Moreover, it is possible that earlier and neglected fossils from sites such as Salé and Thomas Quarries (Morocco), and Ndutu (Tanzania) could be even more ancient members of our species, Homo sapiens.
I used to argue that “anatomically modern humans” (including fossils that essentially look like us today) are the only group that should be called Homo sapiens. Now, I think that anatomically modern humans are only a sub-group within the species Homo sapiens, and that we should recognise the diversity of forms within early Homo sapiens, some of which probably went extinct.
When I set out on my PhD trip in 1971 to study and measure as many as possible of the early modern and Neanderthal skulls curated in European museums, there was one fossil that particularly intrigued me. This was the enigmatic cranium from Jebel Irhoud in Morocco, found a decade earlier, and described as an ‘African Neanderthal’, dated at about 40,000 years old. Imagine my disappointment when I arrived in a Paris museum and was told by an anthropologist that the specimen had just been returned to Morocco. Seeing my crestfallen face over coffee, another worker told me that the fossil was, in fact, locked in a cupboard in the first anthropologist’s room, but he would give me clandestine access to it for a short time the next morning. It was well worth the chicanery and the wait, for as soon as I saw the large but modern-looking face of Jebel Irhoud 1, I knew it was no Neanderthal – it completely lacked their puffed-out cheek bones, midfacial prominence, and enormous nose. But I couldn’t make much sense of Jebel Irhoud in my PhD conclusions as it was apparently too recent and therefore too close in age to actual early modern fossils from Israel and Europe to represent a potential ancestor for modern humans.
Now, Jean-Jacques Hublin and colleagues have published two papers in the journal Nature describing further fossil and archaeological discoveries from Jebel Irhoud, dating both the old and the new material to about 300,000 years old, much more ancient than anyone had previously believed. These finds currently represent the oldest association of probable early members of the H. sapiens lineage and Middle Stone Age tools, and they shift Morocco from a supposed backwater in the evolution of our species to a prominent position. The Irhoud fossils display some primitive features such as a longer, lower braincase, strong browridges, and a large face and teeth, as one might expect at around 300,000 years old. Yet the delicate cheekbones and retracted face look more modern, as do details of the skulls and teeth, and the shape of the jawbones. Associated evidence of the controlled use of fire and the sophistication of the stone tools from Jebel Irhoud also suggest complex behaviour in these early members of our lineage.
How the Irhoud material fits into the bigger picture is not yet clear, as it is likely that different early sapiens populations already existed in different parts of Africa about 300,000 years ago, as well as surviving examples of the more ancient lineages of H. heidelbergensis/rhodesiensis in Central Africa and H. naledi in the South. The Sahara Desert was not always the forbidding barrier it is today, so there may have been human contacts across it at times, and similarities between the Irhoud material and the enigmatic Zuttiyeh and Tabun 2 fossils from Israel may even hint at connections with western Asia too.
Comparing the Irhoud and Sima fossils, we can see that they share comparable primitive features in their bigger faces and smaller brain sizes. But in their differences, they also show that by 300,000 years ago the lineages of H. sapiens and H. neanderthalensis were already diverging strongly from their common ancestor of at least 500,000 years ago. Such a deep division between these lineages may seem surprising, given the fact that they have evidently hybridised successfully in the last 60,000 years, but we now know that it may take 1 to 2 million years for full reproductive isolation to develop between sibling species in birds and mammals, so a separation time of 500,000 years or so would be well within those limits. And such a deep separation time also increases the likelihood that the modern and Neanderthal lineages independently evolved features such as larger brains and smaller teeth, in parallel, in Africa and Eurasia. Whether they could also have independently evolved behavioural traits in tool-making and symbolism remains to be seen.
Also see Stringer C. & Galway-Witham, J. 2017 On the origin of our species. Nature 546: 212-214 [link]
– A Moroccan cradle for Homo sapiens? By Chris Stringer, The Natural History Museum London. This article is reproduced here with the kind permission of the author –