SCIENCE MATTER - It's difficult to know why Neanderthals disappeared

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Who might you meet if you could visit Europe 35,000 years ago?

If you ran across people who looked pretty ordinary, you'd have met Cro-Magnon people, or "European Early Modern Humans." However, you might run across folks who are somewhat shorter and stockier, with heftier bone structures and somewhat protruding foreheads. Such was the appearance of Neanderthals.

Bones of over 400 individual Neanderthals have been unearthed across the vast expanse of Europe, the Middle East, and much of western and central Asia. They existed in one part or another of this region for roughly 200,000 years.

Modern humans started migrating to Europe from Africa only about 40,000 to 50,000 years ago. Though most Neanderthals were gone about 28,000 years ago, a few survived another 4000 years. The last evidence for them is found in Southern Spain on the coast of Gibraltar.

It has been hard to learn about the first 100,000 years of Neanderthal's existence. This was the period of the Last Glacial Age. Glaciers have the nasty habit of wiping out evidence of human-like habitation.

How are Neanderthals related to other humans? Family trees illustrate the lines of descent of individuals, or groups of people, from their ancestors. As with all living things, the family tree for humans is very bush-like.

The broad picture of that tree is not in dispute. However, for closely related ancestors, disagreements occur about the exact nature of the branching. There are a lot of fossils and biomolecular and DNA data that must all fit together to tell a coherent story.

It is still a matter of debate whether Neanderthals are a subspecies of our species or a unique species of their own. Fossil and DNA evidence show the two diverged somewhere between 400,000 and just over 500,000 years ago.

Both are members of the genus Homo. Their last common ancestor was a variety of Homo erectus. There is fossil evidence that, once they diverged, there were a number of intermediaries. The most recent ancestor of Neanderthals is, Homo Heidelbergensis. Their oldest fossils in Europe date to about 600,000 years ago.

It wasn't until 2009 that the Neanderthal genome was completely decoded. Comparison with genomes of modern people from around the globe has shed light on interbreeding between Neanderthals and Cro-Magnons.

A study published in May of this year shows 1 to 4 percent of the genetic material of non-Africans to have Neanderthal origins. The evidence further indicates that whatever interbreeding occurred, it happened shortly after the migration of modern humans out of Africa.

Though the newcomers from Africa coexisted with Neanderthals for well over 10,000 years, there is no evidence of direct conflict. They surely competed for some of the same resources. However, the newcomers had some significantly advantageous skills.

The total population of Neanderthals was never more than a few hundred thousand. They lived in widely separated, small groups. For a long time before moderns appeared, the climate had been one of relatively mild cyclical changes.

Soon after modern humans arrived, those cycles sped up. These circumstances created extreme challenges. In the end, they were simply overwhelmed and, it now seems, to some extent, absorbed by modern humans.

It is becoming increasingly evident they were unlikely to have been the brutish, plodding creatures they are often depicted to be. In fact, their brain sizes were comparable to our own. Recent finds show we have been mistaken about how advanced at least some of them were in tool making.

The northern and southern populations of Neanderthals became separated at some point. Each seems to have adapted to climate change and encroachment of moderns differently. Archeological sites in Southern Italy and the Southern Caucasus Mountains have yielded artifacts that include blade-like stone tools, bone weapons and tools, ochre for coloring, and implements for fishing.

In some of these discoveries, evidence indicates that, though their tools were less sophisticated, they were created and developed independent of influence from modern humans. It would also seem that, in some regions, their hunting skills were not substantially inferior to contemporary Cro-Magnon humans. Neanderthals were probably more intelligent than we once thought.

It is fascinating to see how evidence continues to come together creating an ever sharper picture of human ancestry. New species were spun off branches of the family tree at various times. Sometimes the old line persisted, only to later find itself co-habiting some space with their descendants.

Those descendants would have changed after adapting to the unique environment they occupied during their separation. The extent to which they competed upon finding themselves in overlapping territory depended on the nature of those changes and the demands of their current environment.

Neanderthals were displaced and to a small extent absorbed by Cro-magnon humans. Whether they would have met their demise without the competitive pressure imposed by immigrants from Africa, we probably can never learn. History runs in just one direction, we can't rewind and see if things would be different if circumstances were slightly different.

Steve Luckstead is a medical physicist in the radiation oncology department at Providence St. Mary Medical Center. He can be reached at steveluckstead@charter.net.

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