Didn't catch that cold going around? You just may be part Neanderthal, study sug

[Shonnon]

Didn't catch that cold going around? You just may be part Neanderthal, study suggests.

By Dan McLerran   Thu, Aug 25, 2011




Cross-breeding between modern humans and our archaic cousins some 30,000 or more years ago left a convenient little legacy for some of us today.
Didn't catch that cold going around? You just may be part Neanderthal, study suggests.

If you've noticed that you're visiting the doctor a lot less than most of your friends and neighbors, it could be that you have a distant, ancient archaic human ancestor to thank for that. A recent study by a Stanford University-led research team found that an admixture of certain genes between early modern humans and other species of archaic humans, the Neanderthals and the Denisovans, led to strengthened immune systems among at least some modern humans today.

The researchers performed population genetic studies through gene sequencing to trace the path of various combinations of new variants of immune system genes called the HLA class I genes (which are critical for our body's ability to recognize and destroy pathogens) over the course of early human history. "The HLA gene system, with its diversity of variants, is like a magnifying glass," said key team researcher Laurent Abi-Rached, PhD.  He explained that they provide much more detail and information about the history of populations than typical gene families. The DNA was extracted from ancient bones of Neanderthals and Denisovans, and then used to compare to that extracted from modern humans. Neanderthals are a well-known separate species or sub-species of human who lived from 130,000 to 50,000/30,000 years ago in Eurasia. Their remains have been discovered in relative abundance and have been subject to many years of intense study. Less well known are the Denisovans, evidence of whom was discovered in 2008 by Russian archaeologists working at the site of Denisova Cave in the Altai Mountains of Siberia. They uncovered a small finger bone fragment and tooth, the DNA analysis of which indicated that they belonged to a species of human distinct from both Neanderthal and modern human.  Modern humans, Neanderthals and Denisovans are thought to have coexisted for a time during the late Pleistocene epoch (2,588,000 to 11,700 years BP).

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This 38,000 year-old femur was preserved well enough to allow researchers to extract and sequence Neanderthal DNA. [Image © Science]

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The analysis showed that these diverse species interbred, as new variants of the ancient gene type were found in modern human samples. Moreover, as the gene variants are considered among the building blocks of immune systems, they bestowed a very beneficial legacy.  "The cross breeding wasn't just a random event that happened," says Dr. Peter Parham, leader of the study, "it gave something useful to the gene pool of the modern human."  And that was a stronger immune system, the system responsible for combating unfriendly pathogens in the human body. 

In one class of the HLA gene, researchers estimated that Europeans accounted for about half of their HLA variants to ancient interbreeding with Neanderthals and Denisovans, Asians owed as much as 80 percent, and Papua New Guineans, the most specific of all, as much as 95 percent.

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The archaic HLA genes most likely provided resistance to pathogens that modern humans had not encountered in Africa. Because individuals who possessed the newly-acquired haplotypes then had an advantage over those who did not, they flourished as the new continents became populated. Shown is the worldwide distribution in modern humans for one of the two possible Neanderthal HLA-A-C haplotype sets –the haplotypes are common in Eurasia and not present in Africa. For more information, please see figure 3 in the manuscript. [Image courtesy of Science/AAAS]

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Although the three separate species shared a common ancestor in Africa, they split into separate populations around 400,000 years ago. While Neanderthals migrated into Europe and West Asia, the Denisovans went northeast toward East Asia. Ancestors of modern man, on the other hand, were home bodies. They remained in Africa until about 65,000 years ago, when groups of them began to migrate into Eurasia, encountering their Neanderthal and Denisovan cousins who were by then natives of their habitats and fortified by their acquired new pathogen-fighting genes. Some of those encounters were, shall we say, amorous in nature, and that is where the succeeding modern human populations picked up the new pathogen-fighting genes.

Researchers hope that similar studies can be made by sequencing other gene systems. Says Abi-Rached:  "This is not the pattern seen genome-wide. The HLA system is unique in its diversity and the strength of natural selection acting on it, but it's possible that other gene systems, particularly the ones under similar pressure for variation, could show a similar pattern."

Details of the study will be published in an article appearing online on August 25th at Science Express, the online version of the journal Science.

The study was funded by the National Institutes of Health, the Yerkes Center, the National Science Foundation and the National Cancer Institute.

Cover Photo, Top Left: Reconstruction of a Neanderthal child. Based on research conducted by the Anthropological Institute, University of Zurich.  Christoph P.E. Zollikofer, Public Domain

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