Neanderthal-Human Sex Likely Rare

[ArmorPierce]

http://news.discovery.com/human/neander ... 10913.html

THE GIST
Humans and Neanderthals rarely interbred, suggests a new DNA-based model.
There were likely strong barriers preventing gene flow between the species.

enlargeA replica of an old Neanderthal man at the Neanderthal Museum in Mettmann, Germany. Click to enlarge this image.
Corbis

Modern humans may have some traces of genes from Neanderthals, but a new study suggests any breeding between the two was most likely a rare event.

The new computational model, based on DNA samples from modern humans in France and China, shows successful coupling happened at a rate of less than 2 percent.

The research suggests that either inter-species sex was taboo, or that the hybrid offspring had trouble surviving, according to the findings in the Proceedings of the National Academy of Sciences.

PHOTOS: Faces of Our Ancestors

There may have been "extremely strong barriers to gene flow between the two species because of a very low fitness of human-Neanderthal hybrids, a very strong avoidance of interspecific mating, or a combination," say study researchers at the University of Geneva and the University of Berne in Switzerland.

Between two and four per cent of the human genome can be linked to the long-extinct Neanderthals and their cavemen relatives.


WATCH VIDEO: Does archaeology really include adventures filled with mystery, danger and romance?" The squat, low-browed Neanderthals lived in parts of Europe, Central Asia and the Middle East for up to 300,000 years. But all evidence of them disappears some 40,000 years ago, their last known refuge being Gibraltar.

Why they died out is a matter of some debate, because they co-existed alongside modern humans.

A study by French researchers published in the journal Science last month suggested that modern humans gleaned a competitive immune advantage from their liaisons with cavemen.

NEWS: Sex With Neanderthals Made Us Stronger

But, scientists still have no evidence to suggest the nature of those sexual encounters, whether violent or consensual.

Previous studies have also suggested that Neanderthals were crowded out by modern humans, and that the death blow to their species may have been accelerated by a spate of harsh, wintry weather.

[Anguirus]

Hmm, this is directly contradictory (at least the HEADLINE is) to some work Jerry Coyne was just posting about. I'll have to look into this.

[Dominus Atheos]

This is contradictory to several findings made recently.

How sex with Neanderthals made us stronger

8/25/2011

Mating with Neanderthals and another group of extinct hominids, Denisovans, strengthened the human immune system and left behind evidence in the DNA of people today, according to new research.

The findings add to the growing body of evidence that modern humans who left Africa around 65,000 years ago mated with Neanderthals and Denisovans — two archaic species that lived in Europe and Asia.

The study, which appears in this week's Science, is among the first to show how the interbreeding shaped modern human genes and the attributes they pass to us.

Peter Parham, a professor of cell biology, microbiology and immunology at the Stanford University School of Medicine, and his team focused their analysis on "HLA" genes, which are fast-evolving vital components of the human immune system.

"The modern human populations who left Africa to colonize other continents were likely to have been small groups who started off with limited HLA diversity and suffered further reduction of HLA diversity due to disease," Parham told Discovery News. "Interbreeding with archaic humans introduced additional HLA variants into the modern human population that increased their genetic viability and capacity to resist infection."

He and his colleagues studied the genomes for Neanderthals and Denisovans, as well as the DNA of modern human populations. The organization Bone Marrow Donors Worldwide, as well as bone marrow registries from several countries, provided data on HLA genes.

The analysis shows that Neanderthal and Denisovan HLA genes now represent more than half of such immune system-related DNA in modern European and Asian populations. They also appear to have been later introduced into Africans.

The specific gene HLA-A, for example, is present in the Neanderthal and Denisovan genomes. It contributed this much to the following modern human populations: Up to 95.3 percent for Papua New Guineans, 80.7 percent for Japanese people, 72.2 percent for Chinese people, 51.7 percent for Europeans, and 6.7 percent for Africans.

Such percentages provide clues on how modern humans migrated and interbred. The scientists believe some modern humans migrated out of Africa 67,500 years ago. Interbreeding became evident 50,000 years ago.

"Because archaic humans had lived in Asia and Europe for hundreds of thousands of years before the modern humans arrived, their HLA alleles almost certainly were adapted to the local infections and in this way further invigorated the immune systems of the recent modern migrants," Parham said.

Some of the Europeans and Asians then went back to Africa around 10,000 years ago, bringing the newly acquired genes and their associated immunity boost with them.

Human history was "a lot more complex and interesting" than previously thought, Svante Paabo, director of the Department of Genetics at the Max Planck Institute for Evolutionary Anthropology, told Discovery News.

In separate research, Paabo and his team found that about 4 percent of the genomes of non-Africans are derived from Neanderthals and 4 to 6 percent of modern Melanesian genomes are derived from Denisovans.

This earlier research and the new study then suggest at least two possible scenarios: Either interbreeding was frequent and widespread, involving a lot of individuals, or the majority of native modern populations from certain regions are descended from individuals that did interbreed, even if such "seed" groups were relatively small. Parham suspects the latter is what happened.

While Europe and Asia might now be viewed as a hotbed of interbreeding, modern humans who stayed in Africa appear to have been active interbreeders as well. Neanderthals and Denisovans weren't present, but other archaic human groups likely were.

"Well established is that modern Africans have greater genetic diversity, overall, than the modern populations of other continents," Parham said. "This greater diversity is likely due to what was inherited from earlier forms of Homo, combined with interbreeding between different forms of Homo."

The early ancestors of all modern people, then, did not seem to shy away from breeding with different human species, actions that strengthened our immune systems and likely resulted in other benefits yet to be revealed.

Ancient human DNA still with us

"Archaic" humans interbred with anatomically modern humans in Africa in the last 20,000 to 60,000 years and some of their DNA exists today, researchers said.

Previous studies primarily examined modern human interbreeding with Neanderthals in Europe or other archaic forms in Asia, but a study by University of Arizona geneticist Michael Hammer is the first to definitively suggest interbreeding between separate human forms inside of Africa, a National Science Foundation release said Wednesday.

"It appears some level of interbreeding may have occurred in many parts of the world at different times in human evolution," Hammer, said, adding "Given recent fossil evidence, however, the greatest opportunity for introgression was in Africa" where anatomically modern humans and various archaic forms co-existed for much longer than they did outside of Africa.

Introgression is the movement of genes from one species into the gene pool of another.

"The populations that interbred were similar enough biologically so that they were able to produce fertile offspring, thus allowing genes to flow from one population to the other," he said.

Scientists say they believe contemporary African populations contain a small proportion of genetic material -- about 2 percent -- that moved from a species of archaic humans into the gene pool of anatomically modern humans about 35 thousand years ago.

"This study represents an approach to answering long-standing questions about the contributions of archaic, extinct forms of our genus to the gene pool of our modern human species," said Carolyn Ehardt, program director for biological anthropology at the foundation.

Read more: http://www.upi.com/Science_News/2011/09 ... z1XqtTo2y2

[Johonebesus]

It's not directly contradictory. According to this blog post, the study just suggests that successful matings could have been relatively rare and still allow for a pretty fair amount of gene transfer, especially of advantageous genes. It sounds to me much like the situation with wolves and coyotes. The vast majority of encounters between the two species end with violence, but mating has occurred often enough to create the red wolf and a heavily hybridized coyote population in Canada.



As an aside: I hate to be picky, but is it really so hard to clean up a quoted article? It would take only a few seconds to delete links and captions that end up as bizarre non-sequitur's

[ArmorPierce]

It does not contradict claims that homo sapiens and neanderthals interbred successfully in the slightest. It in fact, acknowledges this. What it does state is that it was a very rare event and the reason this would be is either the offspring would be unfit for survival or that it was considered taboo. Considering that Neanderthal genes have conferred a large degree to our immune system, I find it more likely that the latter was true.

[Broomstick]

Could a third explanation be reduced fertility in the hybrids? If H. sapiens and H. neaderthal were close enough to allow hybrids but distant enough to cause problems with hybridization then matings might have been more common than the evidence shows, but with fewer resulting offspring.

Somewhat analogous - horses and donkeys resulting in mules. Most mules are sterile, but there have been a few, rare, documented cases of female mules conceiving and producing offspring. That would be a situation where in some respects (perhaps immune system, strength, whatever) such human/Neanderthal hybrids might be more fit that either parent but, because of fertility problems, would have trouble passing on such traits.

Or maybe not.

[ArmorPierce]

I could see that falling under 'unfit' for survival. I know a few years ago scientists were unable to answer the compatibility question, don't know if that's still true. Obviously there was some degree of compatibility but was there a large degree of infertile offsprings?

[edaw1982]

I find it difficult to believe sex with neanderthals was "rare". I mean there's the people screwing donkeys in Tiajuana and never mind the whole Welsh/Scots/Kiwi sheepshagging cliche.
And let's not get into the titter-inducing reason people think AIDs passed from Chimp to human.

I mean if some humans go 'Gee sticking my dick in this ungulate sounds like fun' I'm pretty sure someone went 'C'or she's got a big forehead, but at least she has pretty eyes...'
And what happens in Rock Vegas...stays in Rock Vegas.

[The Yosemite Bear]

Though I thought it was a tad uncomfortable as per clan of the cave bear...

[Elfdart]

It's not directly contradictory. According to this blog post, the study just suggests that successful matings could have been relatively rare and still allow for a pretty fair amount of gene transfer, especially of advantageous genes. It sounds to me much like the situation with wolves and coyotes. The vast majority of encounters between the two species end with violence, but mating has occurred often enough to create the red wolf and a heavily hybridized coyote population in Canada.

Two percent is actually fairly high when you think about it. Tigers, lions and leopards are all part of the same genus, yet they only mate under man-made conditions. I'd think the number of successful matings in the wild would be maybe a tiny fraction of 1%.

[Thinktank]

When I was taking anthropology classes, we discussed the Neandethal, Human hybrid topic a
bit. My professor pretty much just shrugged after we went thtrough the science of the time
(the 90's) and surmised that there a helluva' lot of tall brawny human lineages from the "top
of the world" coming out of the last "ice age". Then he reminded us that there are a lot of
myths about giant cannibals from that stage of human lore keeping as well...

So remember, really tall people may suddenly have an urge to eat you.

You have been warned.