Breeding with Neanderthals helped humans go global

When the first modern humans left Africa they were ill-equipped to cope with unfamiliar diseases. But by interbreeding with the local hominins, it seems they picked up genes that protected them and helped them eventually spread across the planet.

The publication of the Neanderthal genome last year offered proof that Homo sapiens bred with Neanderthals after leaving Africa. There is also evidence that suggests they enjoyed intimate relations with other hominins including the Denisovans, a species identified last year from a Siberian fossil.

But what wasn't known is whether the interbreeding made any difference to their evolution. To find out Peter Parham of Stanford University in California took a closer look at the genes they picked up along the way.

He focused on human leukocyte antigens (HLAs), a family of about 200 genes that is essential to our immune system. It also contains some of the most variable human genes: hundreds of versions - or alleles - exist of each gene in the population, allowing our bodies to react to a huge number of disease-causing agents and adapt to new ones.

The humans that left Africa probably carried only a limited number of HLA alleles as they likely travelled in small groups. Worse, their HLAs would have been adapted to African diseases.

When Parham compared the HLA genes of people from different regions of the world with the Neanderthal and Denisovan HLAs, he found evidence that non-African humans picked up new alleles from the hominins they interbred with.

One allele, HLA-C*0702, is common in modern Europeans and Asians but never seen in Africans; Parham found it in the Neanderthal genome, suggesting it made its way into H. sapiens of non-African descent through interbreeding. HLA-A*11 had a similar story: it is mostly found in Asians and never in Africans, and Parham found it in the Denisovan genome, again suggesting its source was interbreeding outside of Africa.

Parham points out that because Neanderthals and Denisovans had lived outside Africa for over 200,000 years by the time they encountered H. sapiens, their HLAs would have been well suited to local diseases, helping to protect migrating H. sapiens too.

While only 6 per cent of the non-African modern human genome comes from other hominins, the share of HLAs acquired during interbreeding is much higher. Half of European HLA-A alleles come from other hominins, says Parham, and that figure rises to 72 per cent for people in China, and over 90 per cent for those in Papua New Guinea.

This suggests they were increasingly selected for as H. sapiens moved east. That could be because humans migrating north would have faced fewer diseases than those heading towards the tropics of south-east Asia, says Chris Stringer of the Natural History Museum in London.

From New Scientist

Early Americans helped colonise Easter Island

South Americans helped colonise Easter Island centuries before Europeans reached it. Clear genetic evidence has, for the first time, given support to elements of this controversial theory showing that while the remote island was mostly colonised from the west, there was also some influx of people from the Americas.

Easter Island is the easternmost island of Polynesia, the scattering of islands that stretches across the Pacific. It is also one of the most remote inhabited islands in the world.

So how did it come to be inhabited in the first place? Genetics, archaeology and linguistics all show that as a whole, Polynesia was colonised from Asia, probably from around Taiwan. The various lines of evidence suggest people began migrating east around 5500 years ago, reached Polynesia 2500 years later, before finally gaining Easter Island after another 1500 years.

But the Norwegian adventurer Thor Heyerdahl thought otherwise. In the mid-20th century, he claimed that the famous Easter Island statues were similar to those at Tiahuanaco at Lake Titicaca in Bolivia, so people from South America must have travelled west across the Pacific to Polynesia. His famous Kon-Tiki expedition, in which he sailed a balsa wood raft from Peru to the Tuamotu islands of French Polynesia, showed that the trip could have been made. But if it was made, no trace remained.

Now Erik Thorsby of the University of Oslo in Norway has found clear evidence to support elements of Heyerdahl's hypothesis. In 1971 and 2008 he collected blood samples from Easter Islanders whose ancestors had not interbred with Europeans and other visitors to the island.

Thorsby looked at the HLA genes, which vary greatly from person to person. Most of the islanders' HLA genes were Polynesian, but a few of them also carried HLA genes only previously found in Native American populations.

Genetic shuffling

Because most of Thorsby's volunteers came from one extended family, he was able to work out when the HLA genes entered their lineage. The most probable first known carrier was a woman named Maria Aquala, born in 1846. Crucially, that was before the slave traders arrived in the 1860s and began interbreeding with the islanders.

But the genes may have been around for longer than that. Thorsby found that in some cases the Polynesian and American HLA genes were shuffled together, the result of a process known "recombination". This is rare in HLA genes, meaning the American genes would need to be around for a certain amount of time for it to happen. Thorsby can't put a precise date on it, but says it is likely that Americans reached Easter Island before it was "discovered" by Europeans in 1722.

Thorsby says there may have been a Kon-Tiki-style voyage from South America to Polynesia. Alternatively, Polynesians may have travelled east to South America, and then returned. There is already evidence for that: chicken bones found in Chile turned out to be Polynesian, so we know that the eastward journey did happen at some stage.

However, Thorsby's findings don't mean that Heyerdahl's ideas have been vindicated. The first settlers to Polynesia came from Asia, and they made the biggest contribution to the population. "Heyerdahl was wrong," Thorsby says, "but not completely."

From New Scientist

Neanderthals: Bad luck and its part in their downfall

As our ancestors moved north out of Africa and onto the doorstep to the rest of the world, they came across their long-lost cousins: the Neanderthals. As the popular story goes, the brutish hominins were simply no match for cultured, intelligent Homo sapiens and quickly went extinct.

Maybe, but it's also possible that Neanderthals were simply unlucky and disappeared by chance, mathematicians propose.

We know that humans and Neanderthals got pretty cosy during their time together in the Middle East, 45,000 years ago. Between 1 and 4 per cent of the DNA of modern non-Africans is of Neanderthal origin, implying their ancestors must have interbred before humans moved into Europe.

The popular theory has it that humans soon displaced Neanderthals thanks to their superior skills and adaptations. But mathematicians Armando Neves at the Federal University of Minas Gerais in Belo Horizonte, Brazil, and Maurizio Serva at the University of Aquila, Italy, now say that the extinction of Neanderthals may have been down to a genetic lottery.

When two populations interbreed, one of them can go extinct simply due to the random mixing of their genes through sexual reproduction.

To find out if this could have wiped out Neanderthals, Neves and Serva modelled the populations that met in the Middle East. Using very few assumptions, they estimated the rate of interbreeding that would lead to the observed share of Neanderthal DNA.

Their results suggest that the 1 to 4 per cent genetic mix could have come about with one interbreeding every 10 to 80 generations. The time taken to reach this mix would depend on the size of the populations. But regardless of populations, Neves and Serva's model shows that low rates of interbreeding could theoretically have led to the extinction of Neanderthals through a genetic lottery.

"The observed low fraction of Neanderthal DNA could easily have arisen quite naturally even if Neanderthals weren't inferior," says Neves.

A strong point of the analysis, says anthropologist Luke Premo of the University of Washington in Pullman, is that it makes few assumptions about unknown factors, including the relative sizes of the African and Neanderthal populations at the time.

Nevertheless, says Premo, the evidence for some kind of superiority of the African group is still strong. "Humans were expanding while Neanderthals were fairly restricted to a portion of Eurasia," he says. "Given their larger population and expansion, it appears that humans were bound to win out."

From New Scientist

DNA, IT'S INVADING! - The Spaz Speaks!

Hi y'all, I don't post here often, but I'm going to try to step it up. Call me Davenport, or "The Spaz."

Anywho, I saw this little bit of sexy on the interweb and thought I'd throw it down.

Scientists at Edinburgh University, after sampling Scots from several different locales, have concluded that Ireland genetics invaded Scotland before what is currently suggested by the historical record. (Original Source)

This not only shakes the historical record a bit, but it also manages to throw up talk of trade route patterns and settlement distribution. Aside from that the testing showed possible Viking ancestry in different groups as well as a strong genetic divide between the East and West, in England.

Thoughts?

--The Spaz