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Neanderthals and Denisovans, two archaic hominid species, have been shown by genetic tests to have interbred with human migrants in Europe and Asia.  (Source: Corbis)

Researchers speculate that such sexual attractions between the species were rare, but that the children were much more genetically fit, so came to dominate the population.  (Source: Google Images)

The highest rates of Denisovan DNA occurrence were found in the DNA of natives of Papua New Guinea.  (Source: Flickr)

The immune proteins our hominid relatives gave to us during interbreeding made us hardier and more resist to potentially deadly infections.  (Source: Paul de Bakker)
Turns out Europeans and Asians may be the least "genetically pure" homo-sapiens

It turns out that European DNA, like that of Asians and Africans, has traces of archaic hominids mixed in with the familiar Homo sapien-specific stretches.

The sequencing of the Neanderthal genome
 has led to some incredible discoveries -- among them, that humans were having sex with Neanderthals.  A pair of new studies has shown that Neanderthal genes aren't evenly distributed throughout the entire human population -- rather some populations have more or less of them.

A new study, whose senior author is 
Peter Parham, a professor of cell biology, microbiology and immunology at the Stanford University School of Medicine, examines how interbreeding with our closely related hominids led to a superior human immune system.

Svante Pääbo, director of the Department of Genetics at the Max Planck Institute for Evolutionary Anthropology and senior author on the paper [abstract] detailing the original Neanderthal genome draft, suggests that one of two possibilities occurred.  Either migrants to Asian and Europe broadly had sex with Neanderthals or just a few did, but whose progeny survived in greater numbers, passing on the early hominids' genetic material.  Researchers believe the latter explanation is more likely the case.

Humans are thought to have migrated from Africa around 67,500 years ago, spreading to Asia and Europe.  In these regions they encountered Neanderthals and Denisovans -- another archaic hominid, who they at least occasionally engaged in sexual intercourse with.  Interbreeding is thought to have occurred starting around 50,000 years ago.

Those hairy charmers passed something valuable along to the migrants -- improved immunity.  Many of Eurasians'  HLA genes -- fast evolving human immune system components -- are thought to have been "borrowed" from the Neanderthal and Denisovan genome.

It found that one Denisovan-derived gene -- HLA-A  -- was 95 percent likely to occur in residents of Papua New Guinea, 70 percent in residents of China, 50 percent in Europe, and virtually non-present in Africa.

The genes are thought to have conferred improved survival rates on the migrants, as they gained defenses against local diseases, which took their archaic hominid co-inhabitants millennia to develop.

Africans, who never personally interbred with the Denisovans and Neanderthals did receive a bit of these genes second hand, from migrants who returned to the region around 10,000 years ago.  And they are thought to have an even stronger and more diverse immune system, as they bred with other species of archaic hominids
, which were native to Africa.

Previous studies have shown that non-Africans have around 4 percent Neanderthal genes, while Melanesians -- natives of Indonesia and the surrounding islands -- also have 4 to 6 percent of their genes derived from the Denisovans.

The study on the project is published
 [abstract] in the prestigious peer-reviewed journal Science.

The new work could offer some additional explanation of why Native Americans may have been so susceptible to diseases brought to the New World by Europeans and Africans.  Native Americans may have missed much of the interbreeding opportunities.  Thus while they may be the most "pure" examples of Homo sapiens DNA, that may have proved fatal to many of them.



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discovering more leads to knowing less.
By drycrust3 on 8/26/2011 6:09:05 PM , Rating: 4
I can't understand how it is that after analysing all these different species' genome in great detail that you end up not knowing when one animal is or isn't the same species as another. Is a German Shepard dog the same species as a poodle? It was, but now it would be considered as a different species with genes taken from the poodle (or the other way around).
Or is a bird the same species as a spider? It may seem obvious that it isn't, but since there is no clear cut boundary of difference between on one group of genome and another, then anyone can define whether one group of genomes is the same as another (so they are the same species) is different (so they are different species).
This is a very unscientific approach. There should be enough genomes analysed by now that scientists should be able to determine that a German Shepard is the same species as a poodle, and that a bird isn't a spider.
The result of all this ambiguity is that we have a whole lot of human ancestors that aren't considered humans, not because they weren't our ancestors, nor because the difference in that group of genomes passes a threshold that normally indicates a difference in species, but just because someone liked the idea of those people being different a different species from us.




RE: discovering more leads to knowing less.
By Gurthang on 8/26/2011 10:27:27 PM , Rating: 5
The taxonomy we use to describe the relationships of organizms here on earth is an imprecise beast. Animals do not come with little books in their back pockets containing complete ansestral trees.

Though it helps to have a basic definition of species. In general it is a group of like animals (in form and behavior) that live in the same geographic area and that are able to breed with each other.

As to speciation through husbandry like domestic dogs. Although they display a wide variety of physcal traits. I suspect most are controlled from just a small set of genetic changes and since these changes are not localized for most they just fall into the accepted morphic range of the domestic dog species.

Another thing to remember is our genes are like an undocumented open soource project they change over time accumulating new things and forking and combining into many other projects. And by looking at today's code you may see parts and ideas from ancient projects long gone but deciding how two programs are really related from just the code will always be challenging and the decision of where to draw the "line" may at times seem arbitary.


By Iketh on 8/27/2011 2:24:02 PM , Rating: 2
Considering we came to inhabit the same area as neanderthals, and we mated, and are certainly a like in form and behavior, we are the same species. Or are neanderthals considered a subspecies?

Maybe these findings will reclassify them as an ancient race?


By Paj on 9/1/2011 7:28:35 AM , Rating: 2
Yep. The idea of a species being clearly distinct from other organisms within a taxonomy is a legacy from Victorian era science - the more we discover about genetics, the more the previously clearly defined boundaries start to shift, change or disappear altogether.


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