24 September 2010

Volcanos And Early Human Migration

Into Asia

Stone age tools found in India and the Arabian Peninsula starting about 70,000 to 80,000 years ago suggest that migration to Asia (commonly called the "Southern Route") happened earlier than the 60,000 years ago date sometimes suggested (largely based on genetic mutation rate evidence), and the placement of these tools suggest that the migration was inland rather than coastal. The tools were found both above and below ash from the major volcanic Toba eruption around 74,000 years ago.

The older remains are more notable, as they argue against the hypothesis that the Toba eruptions wiped out the pre-modern humans creating an ecological vacuum into which modern humans migrated.

The investigators think that an Out of Africa migration could be as old as 120,000 years ago, but it isn't perfectly clear that the migrants were modern humans as opposed, for example, to Neanderthals.

Into Europe

Modern human penetration into Europe beyond the Middle East is widely believed to have come later, and there is no doubt that it was preceded by hundreds of thousands of years of Neanderthal occupation.

There is likewise no doubt that there are no modern humans with large Neanderthal genetic roots. Patrilineal and matrilineal comparisons of Neanderthal DNA to modern human DNA provided no evidence of any genetic relationship between the two populations. Newer studies comparing the entire Neanderthal genome to the entire modern human genome show a 1% to 4% genetic contribution to modern humans outside of Africa from Neanderthals that shows no geographic trend among non-Africans.

So the questions that are open are: When did modern humans arrive? What kind of interactions did they have with Neanderthals? Why did Neanderthals go extinct?

The predominant view is that modern humans who were hunters and gatherers arrived in Europe around 38,000 to 50,000 years ago. Conventional wisdom is that modern humans who arrived had social and genetic traits that gave them a selective advantage over Neanderthals which caused Neanderthal extinction by some combination of getting a larger share of available hunting and gathering resources, adapting better to changing climate, and killing off the Neanderthals. And conventional wisdom is that Neanderthals spent time co-existing but not producing many hybrid children for extended periods at the fringe of a modern human advance and a Neanderthal retreat whose boundary moved over time.

But, the fact that there appeared to be a 1% to 4% Neanderthal component to the non-African modern human genome which does not increase in areas where one would have expected that there would have been more sustained periods of Neanderthal and modern human cohabitation of the same regions seems to undermine this hypothesis the suggestion that there was a moving fringe of interaction between Neanderthals and modern humans over a long period of time. There is also dispute over how much of the difference in material culture between Neanderthals and modern humans was due to genetically determined brain capacity and how much was learned.

Some new studies point to climate change due to volcanic eruptions as a factor that greatly reduced Neanderthal populations, possibly even leading to their extinction in much of their range, creating a largely uninhabited wilderness for modern humans to move into in Europe, and helping to explain why modern humans arrived in Europe so much later than the did in Asia.

These studies suggest that at least "three volcanic eruptions about 40,000 years ago devastated Neanderthals’ western Asian and European homelands" clearly the way for modern humans to move in after a period of interaction between the populations in the Middle East.

A study of layers of material of a cave in the Russian Caucuses suggest that there were two "separate volcanic eruptions in western Asia between 45,000 and 40,000 years ago" that produced cold and dry conditions. This coincides with changing material culture in the cave:

Signs of Neandertal activity at Mezmaiskaya Cave declined sharply after the first western Asian volcanic eruption and disappeared after the second blast, the researchers say. By 40,000 years ago, cave sediment contains no bones of hunted animals or Neandertal-made stone tools.

Thin, double-edged stones, perforated shells for stringing on necklaces, bone points and other items characteristic of Stone Age H. sapiens turn up between 38,000 and 37,000 years ago in Mezmaiskaya Cave.

Another study in Italy "reported evidence of an unusually large volcanic eruption in Italy around 40,000 years ago. That event created a 'volcanic winter' that devastated the ecology of southern and eastern Europe."

But, "[e]xcavations in four southern Mediterranean caves have unearthed modern human tools that, contrary to the new proposal, are slightly older than ash layers from the 40,000-year-old volcanic eruption in Italy."

Ancient Neanderthal DNA evidence suggests that the entire Neanderthal population of Europe may have been in the mid-thousands to low tens of thousands of individuals, spread over a huge area in several somewhat distinct populations and relied heavily on killing large game, while modern humans who followed appear to have had a more diverse diet, higher population density and more sophisticated material culture.

While Neanderthals previous strong track record of surviving ice ages casts some doubt on the ability of a cold trend to bring them down, if volcanoes made this happen in a matter of months or years, rather than centuries or millenia, they might not have been able to adapt to the changes quickly enough to lose their fragile foothold on survival and had their numbers dramatically reduced, making it much harder for them to hold territory vis-a-vis new modern human arrivals.

Recent Pre-History

Rounding out these new finds are some new reports on the early pre-agricultural life of modern humans.

A site at an Israeli cave shows signs of feasting by a group of about "35 members of the Natufian culture gathered" on tortise meat and wild cattle at funerals about 12,000 years ago, before agriculture was invented. Earlier studies had only found post-agricultural feasts dating to 9,500 years ago.

They were probably proto-agriculturalists, relying on wild versions of plants and animals that would later be domesticated for food and staying in the same area to exploit this bounty year round.

Natufian population growth stoked a need for community-building rituals, such as feasting, the researchers propose. These social changes occurred at the same time as this ancient society intensified its use of wild plants and game that people living in the region later domesticated. . . . Natufian people lived from around 15,000 to 11,500 years ago in the Middle East. Theirs was the first known society to inhabit year-round settlements.

New evidence of the area where the body of an "iceman" found in the Alps who died around 5,000 years ago also shows that rather than dying there, he was probably given a funeral there and that his body rolled downhill from his grave site.

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