In to Asia – Wisdom Hidden in Silence

Modern humans arose only once, in Africa, about 200,000 years ago. They then spread across Eurasia some time after 60,000 years ago, replacing whatever indigenous populations they met with no interbreeding. This is the ‘Out of Africa’ model, as it’s commonly known. In the 1990s, the hypothesis found widespread acceptance by palaeoanthropologists, especially when the first analyses of Neanderthal DNA seemed to indicate that Neanderthals and modern humans did not interbreed. But this popular idea is in need of revision, particularly given the number of important findings across Asia over the past few decades.

For instance, with the discovery of the ‘Hobbit’ (Homo floresiensis), a species that seems to have stood about four feet high, it became clear that several different hominin taxa were present across the landscape during the Late Pleistocene (12,000-127,000 years ago). Many new hominin fossils found over the past decade, particularly in China, are now tentatively dated as older than 60,000 years, calling into question the idea that modern humans migrated out of Africa only 60,000 years ago. Take the recent discoveryof two modern human teeth found in the Luna cave in China’s Guangxi Zhuang Autonomous Region. When my research team and I dated the flowstones – rock that forms from precipitation inside a cave – directly above and below the location of the two human teeth using an absolute dating method called uranium-series, we found that the human teeth dated to between 70,000 and 126,000 years ago; a situation clearly impossible if modern humans moved out of Africa only 60,000 years ago.

So with findings such as these, what happened exactly? Where does the most current data suggest we came from? This is how the story is shaping up today.

The first question we should ask is why did modern humans – now thought to have emerged around 315,000 years ago – leave Africa to begin with? If a population is perfectly acclimated to a particular environment and has access to an abundance of resources, then there really is no reason to move or change. For instance, tarsiers – those cute nonhuman primates the size of your hand with huge, buggy eyes – have a set of teeth that has hardly changed over the course of millions of years, indicating that they found a niche that has worked for them – and happily stayed put.

However, tarsiers did move from Europe to their present home of Southeast Asia due to a changing environment. So what happened with humans? Some researchers have suggested that population density increased to the point where smaller human foraging groups were forced to explore new lands. Others have suggested that due to major environmental events in East Africa (eg, a major desiccation event around 60,000 years ago) humans were prompted to find greener pastures. Yet another explanation could simply be that early modern humans were following the large game that they relied on, and these food packages moved out of Africa across land bridges without realising that they were actually moving from one continent to another.

This brings us to another question: by which route did modern humans move out of Africa? No clear routes across the Mediterranean from North Africa appear to be present, so the earlier dispersals out of Africa and into Eurasia might have been across the Arabian Peninsula. One possibility is that they crossed the Bab-el-Mandeb Strait to Yemen (which would have required a water-crossing even during major glacial stages), but more likely they travelled from northern Egypt to the Sinai Peninsula. Dispersals into the Levant began sometime after 200,000 years ago, as recent evidencefrom the Misliya cave in Israel indicates. Early modern humans reached as far north as Israel, as represented by sites such as Misliya, Qafzeh and Skhul. But most of the earlier dispersals appear to have followed a more southerly route, skirting the intimidating Himalayan mountain range and the Qinghai-Tibetan Plateau to eventually reach central China, mainland Southeast Asia and Australia. These earlier dispersals of Homo sapienswere much smaller in scale than later migrations. But as genetic technology to sequence much older DNA improves, we are beginning to discern traces of these earlier dispersals in the record. Indeed, a recent genetic studypublished in Naturefound that about 2 per cent of the DNA of the modern Papua New Guinea peoples was represented by these earlier dispersals.

There is still a tremendous amount of research to do in Asian palaeoanthropology. The increasing number of contributions coming out of Asia is forcing scholars to rethink how they view various modern human origin models. Indeed, just this January, a studyin Scienceindicated that the earliest modern humans in Asia date to between 177,000 and 194,000 years ago from the Misliya cave in Israel. It seems as if, every few weeks now, a new hominin fossil, genetic study, archaeological site, or re-dating of old sites is reported from the vast Asian continent, a continent that still has large swathes of areas yet to be intensively explored. If nothing else, the picture as it appears thus far is much more complicated than the old Out-of-Africa models: there were multiple earlier dispersals from Africa, and much more interbreeding between species than we once thought. The story of ourselves, it turns out, becomes richer the more we know about it.