Modern man's true origin?
2008-01-01 21:54
Chicago - For more than 150 years, a debate has raged over the origins of modern man.
The main body of scientific thought says modern humans migrated from Africa and then overwhelmed their more primitive European counterparts, the heavy-browed Neanderthals, or inter-bred with them.
But growing credence is being given to the theory that homo sapiens evolved from the Neanderthals, who mysteriously died out some 28 000 years ago.
A new study to be published on Wednesday in Proceedings of the National Academy of Sciences says evidence of huge climate change supports that theory.
Harsh weather
Eugene Morin, an anthropology professor at Laval University in Quebec, argues that an extended period of harsh weather would have made Western Europe unwelcoming to new migrants at the time when the tools and cave drawings of modern man began to appear.
He says it is much more likely that Neanderthals evolved as a result of these climate changes which drastically reduced the diversity and availability of animals to hunt.
"If the Neanderthals were already having trouble how would it have been possible for another population to survive?" he argued.
"Even if they had a selective advantage they would still be facing the climatic conditions ... and would be competing with Neanderthals which would have been locally adapted."
Morin examined the animal bones discovered at a rich archaeological site in Saint-Cesaire, France and determined that the consumption of reindeer increased from 30% to 87% of the cave-dwellers' diet from about 40nbsp;000 to about 35 000 years ago.
And since a similar pattern was found in the bones of smaller mammals such as mice and voles, Morin was able to conclude that a "relatively rapid" climatic change resulted in a drop-off in the region's bison and horse herds.
This climate change was as dramatic as the difference between the temperate forests near Montreal and the sparse Arctic region to the north, he explained.
With their survival tied to unstable reindeer herds subject to frequent crashes, the population density of Neanderthals in the region dropped dramatically, Morin surmised.
Population bottleneck
This created a "population bottleneck" in which the genetic diversity of Neanderthals was dramatically reduced, allowing rare mutations to become fixed, Morin concluded.
It's also possible that the harsh conditions forced the hunter-gathering Neanderthals to roam farther afield in search of food and to expand their social networks in order to protect themselves from hard times.
This may also have helped spread the genetic traits found in Cro-Magnons and the use of more complex tools and cave paintings.
Morin said: "It remains a mystery why all these changes occurred together, but I don't think they occurred as a result of a modern-human migration.
"A lot of people have argued for a population increase (as modern man expanded both numerically and spatially) and this study has shown that is not possible."