Wednesday, February 29, 2012

DNA Clues On Neanderthal Disappearance

Conclusions based on thirteen samples are at best suspect and this lot is no different.  The underlying assumption is that the Neanderthals were somehow inferior and thus died out.   Yet they had one extra gene than we do.

The evidence, by the by, conforms nicely to my conjecture that the Neanderthals migrated to the continental shelf and participated in the first rise of human modernity.  We have even tightened up the time frame to 48,000 years ago.  That a select population reentered the original homelands is not unreasonable at all in this scenario.

My point is to rid ourselves of a very dangerous assumption that has dogged research on Neanderthals for a century. They are not deficient humanity at all and may well have been far better adapted to harsh temperate climes than we ever were.  The proposition that they helped in the first human emergence is quite reasonable.

What the evidence does do is sharply underline the importance of the transitional date of 48,000 year ago when the Neanderthals effectively vacated the continental climate zone.  Plausibly they discovered lowland agriculture and made a far easier living, just like today when no one relies on hunting whatsoever anymore even if they could.

DNA reveals Neanderthal extinction clues

By Paul RinconScience editor, BBC News website

Neanderthals were close evolutionary cousins of our own species - Homo sapiens

27 February 2012 Last updated at 13:14 ET

Neanderthals were already on the verge of extinction in Europe by the time modern humans arrived on the scene, a study suggests.

DNA analysis suggests most Neanderthals in western Europe died out as early as 50,000 years ago - thousands of years before our own species appeared.

A small group of Neanderthals then recolonised parts of Europe, surviving for 10,000 years before vanishing.

An international team of researchers studied the variation, or diversity, in mitochondrial DNA extracted from the bones of 13 Neanderthals.

This type of genetic information is passed down on the maternal line; because cells contain multiple copies of the mitochondrial genome, this DNA is easier to extract from ancient remains than the DNA found in the nuclei of cells.

The fossil specimens came from Europe and Asia and span a time period ranging from 100,000 years ago to about 35,000 years ago.

The scientists found that west European fossils with ages older than 48,000 years, along with Neanderthal specimens from Asia, showed considerable genetic variation.

But specimens from western Europe younger than 48,000 years showed much less genetic diversity (variation in the older remains and the Asian Neanderthals was six-fold greater than in the western examples).

Neanderthals may have been more sensitive to the dramatic climate changes... than was previously thought”

Love DalenSwedish Museum of Natural History

In their scientific paper, the scientists propose that some event - possibly changes in the climate - caused Neanderthal populations in the West to crash around 50,000 years ago.
But populations may have survived in warmer southern refuges, allowing the later re-expansion.

Low genetic variation can make a species less resilient to changes in its environment, and place it at increased risk of extinction.

"The fact that Neanderthals in Europe were nearly extinct, but then recovered, and that all this took place long before they came into contact with modern humans, came as a complete surprise," said lead author Love Dalen, from the Swedish Museum of Natural History in Stockholm.

"This indicates that the Neanderthals may have been more sensitive to the dramatic climate changes that took place in the last Ice Age than was previously thought."

Neanderthals were close evolutionary cousins of modern humans, and once inhabited Europe, the Middle East and Central Asia. The reasons behind their demise remain the subject of debate.

The appearance of modern humans in Europe around the time of the Neanderthal extinction offers circumstantial evidence that Homo sapiens played a role. But changes in the climate and other factors may have been important contributors.

"The amount of genetic variation in geologically older Neanderthals as well as in Asian Neandertals was just as great as in modern humans as a species," said co-author Anders Gotherstrom, from Uppsala University.

"The variation among later European Neanderthals was not even as high as that of modern humans in Iceland."

The researchers note that the loss of genetic diversity in west European Neanderthals coincided with a climatic episode known as Marine Isotope Stage Three, which was characterised by several brief periods of freezing temperatures.

These cold periods are thought to have been caused by a disturbance of oceanic currents in the North Atlantic, and it is possible that they had a particularly strong impact on the environment in western Europe, note the researchers.

Over the last few decades, research has shown that Neanderthals were undeserving of their brutish reputation.

Researchers recently announced that paintings of seals found in caves at Nerja, southern Spain, might date to 42,000 years - potentially making them the only known art created by Neanderthals. However, this interpretation remains controversial.

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