The Mayans and the Neanderthals

Last week I was reading a news article about a new study that determined that Tibetans inherited a gene that gives them high-altitude tolerance from ancient Denisovans. Denisovans, you may recall, are an extinct human species known primarily by their DNA, that are genetically closer to Neanderthals than us. That Denisovan DNA made it into modern humans is not anything new, but apparently this particular gene variant went extinct except for among Tibetans and some Chinese.

That's interesting in and of itself. However, at the end of the article I read this:

The discovery is the second case in which modern humans have acquired a trait from archaic humans, notes paleogeneticist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, whose team discovered the Denisovan people. Earlier this year, another team showed that Mayans, in particular, have inherited a gene variant from Neandertals that increases the risk for diabetes.

Wait, what? How did Neanderthal DNA get into Mayans?

A paper published last February reported the results of researchers looking for genetic associations with type 2 diabetes in Mexicans and other Latin Americans. They looked at 9.2 million single nucleotide polymorphisms (SNPs) from 3,848 Mexicans with type 2 diabetes, compared with a similar number of non-diabetics. The scientists found a chunk of the genome where a certain variant containing 5 particular mutations was associated with diabetes. When they looked at other populations, they found the following:

I have simplified their table a little bit. It shows the percent of samples that had the most common version of the gene compared with the version associated with diabetes. You can see that it is hardly found anywhere except among east Asians and Mexicans. Further, when they looked at samples with over 95% Native American DNA, they found the mutant version in about half.

So let's summarize what they found so far: A gene variant associated with type 2 diabetes that is commonly found among Native Americans can also be found among east Asians, but only rarely in Europeans and Africans. That makes sense since Native Americans are descended from east Asians. But what does that have to do with Neanderthals?

Well, in looking at the variant the scientists determine that it diverged from the European version about 800,000 years ago. Modern humans didn't even exist back then, and Africans don't have it, so how could these differences have arisen? It turns out that an unpublished Neanderthal genome has a nearly identical match. Thus, it appears that ancient Asians picked up the gene from Neanderthals. It was then carried into America, and for some reason it is now common among Native Americans.

I didn't find any reference to Mayans in the paper (although I didn't look in the supplementary material) so I'm not sure where that came from, but many Mayans probably did have this gene. Lest you think that Native Americans are special in their inheritance of Neanderthal DNA, the authors point out,

...whereas this particular Neanderthal-derived haplotype is common in the Americas, Latin Americans have the same proportion of Neanderthal ancestry genome-wide as other Eurasian populations (2%)

In other words, many of us have about the same amount of Neanderthal DNA [1], just different parts.

Notes:

1. Africans have little to no Neanderthal DNA because their ancestors remained in Africa and never met Neanderthals.

Source: SIGMA Type 2 Diabetes Consortium, Sequence variants in SLC16A11 are a common risk factor for type 2 diabetes in Mexico, Nature. 2014 Feb 6;506(7486):97-101

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Scientists: Bigfoot Still Missing

University of Oxford scientists have published--in a peer-reviewed journal--results of DNA tests for 'anomalous primates' (i.e. Bigfoot). They put out a call for people to send in hair samples and received 57. Actually, not all of the samples were hair, so after they discarded those and others from which DNA could not be extracted, they were left with 30 samples. They sequenced the mitochondrial DNA of the remaining samples and compared the sequences to those in databases. They found polar bear, horse, raccoon, porcupine, dog, and even one human. None of the results came back as not-quite-human. It wasn't a total waste of time though, because a couple of samples from the Himalayas came back as polar bear, suggesting a hybrid species of bears.

The authors conclude:

While it is important to bear in mind that absence of evidence is not evidence of absence and this survey cannot refute the existence of anomalous primates, neither has it found any evidence in support. Rather than persisting in the view that they have been ‘rejected by science’, advocates in the cryptozoology community have more work to do in order to produce convincing evidence for anomalous primates and now have the means to do so.

I think that's a diplomatic way of saying put up or shut up.

Notes:
Source: Sykes, Proc. R. Soc. B 22 August 2014 vol. 281 no. 1789

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