Human Neanderthal Interbreeding (11/8/2006)

Researchers with the Howard Hughes Medical Institute and the University of Chicago have published a paper in the Proceedings of the National Academy of Sciences, that provides circumstantial evidence that humans and Neanderthals interbred at some point in history.

Neanderthals and humans lived side by side in Europe for tens of thousands of years. Physiologically Neanderthals were very similar to humans (see picture). Recent archaeological evidence at Gorham's Cave suggests that Humans and Neanderthals may have even lived in the same caves together.

Neanderthals died out about 35,000 years ago for some unknown reason. Some scientists have suggested that they interbred with humans, and "bred" themselves out of existence. Others have suggested that there high protein diet forced them to hunt animals like the wholly mammoth and wholly rhino into extinction thus eliminating there primary source of food.

Bruce Lahn, a Howard Hughes Medical Institute researcher at the University of Chicago who led the study said "Finding evidence of mixing is not all that surprising. But our study demonstrates the possibility that interbreeding contributed advantageous variants into the human gene pool that subsequently spread."

Mr. Lahn's team found a gene that regulates brain size to have entered the human genome about 1.1 million years ago, and that it's modern form, or allele, appeared about 37,000 years ago, right before the Neanderthals went missing. The gene microcephalin (MCPH1) it thought to control brain size while in the womb.

The gene also shows signs that it has experienced positive selection. Positive selection happens when a gene passed on some advantage, to that the people who had it were more likely to reproduce than people who didn't have the gene. Mr. Lahn's team estimated that 70 percent of all people living today have this gene.

Mr. Lahn also said "By no means do these findings constitute definitive proof that a Neanderthal was the source of the original copy of the D allele. However, our evidence shows that it is one of the best candidates,"

The researchers came to their conclusions by performing statistical analysis of the DNA sequence that contains microcephalin, which is known to regulate brain size in humans. Mutations in the human gene cause the brain to develop much smaller than normal, in a condition called microcephaly. By tracking these mutations the researchers could determine the date of the original genetic variant to 37,000 years ago.

They also noted that this D allele is very common in Europe, where the Neanderthals lived, and is more rare in Africa, where they did not. Though the evidence is circumstantial at best, research on the Neanderthal genome should be able to clear things up.

Comments:

Leave a Reply: