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Tens of thousands of years ago modern humans got frisky with our cousins, the Neanderthals. We inherited several genes from this rendezvous, some of which proved beneficial and helped our ancestors adapt to the new environments they encountered as they spread through Europe. However, not everything we got from Homo neanderthalensis proved beneficial. The genetic gulf between our two species meant that any hybrids would probably have a few genetic problems. Like how when tigers and lions mate the resulting ligers are typically sterile.

Vernot and Akey – the two researchers behind last weeks discovery that Neanderthal genes helped humans adapt – noted that the genes we inherited from Neanderthals are pretty evenly spread throughout the genome. However, there are some parts where there are no Neanderthal genes. This strongly suggests that the Neanderthal genes present in those regions were harmful, so have been removed via natural selection. Last Wednesday a report was published in Nature, delving further into the negative side-effects of breeding with Neanderthals. The researchers honed in on the “deserts” of Neanderthal genes, hoping to infer what the harmful genes which were removed might have done.

They found 4 regions in the European genome, and 14 in the East Asian genome, that were unusually devoid of Neanderthal genes. This could be explained by the fact that there were likely a small number of hybrids, so many genes were just lost by chance. However, many of these absent regions code for important things, which raises the possibility that there were genes there, but they were removed because they were harmful.

The largest of these useful deserts was located on the X chromosome, where many of the genes relating to male fertility are found. Given the fact that many modern hybrids are sterile, it’s obvious that genes relating to fertility are especially susceptible to being mucked up by hybridisation. So maybe the first Neanderthal/human hybrids had some fertility issues, which led to the Neanderthal genes relating to fertility being stripped from the genome by natural selection. They also found such deserts in regions of the genome which are conserved in modern humans. These are regions which have not changed much over the course of evolution, likely because they are so finely adapted that any change would be detrimental. In these regions apparently mixing with Neanderthals was also enough to tip them over the edge.

However, not all of the harmful genes we inherited from Neanderthals have been removed. They cross-reference the Neanderthal genes still in our genome with those associated with several diseases, including “lupus, biliary cirrhosis, Crohn’s disease…smoking behaviour…and type 2 diabetes“.

Turns out House was wrong, this time it was lupus.


Sankararaman, S., Mallick, S., Dannemann, M., Prüfer, K., Kelso, J., Pääbo, S., … & Reich, D. (2014). The genomic landscape of Neanderthal ancestry in present-day humans. Nature.

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Cynthia Echterling · 5th February 2014 at 9:08 pm

I read an article in which they stated that Neanderthal genes caused diabetes in Native Americans also, but I was wondering about that. Having genes that allow cells to metabolize nutrients more efficiently helped humans survive for thousands of years even in times of scarcity. Is the fault with the genes or the modern diet of processed carbohydrates? Kind of like putting race car fuel in a fuel efficient car.

    Adam Benton · 6th February 2014 at 12:12 pm

    They didn’t examine Native American genes in the study I read, but they are descended from East Asians so I assume the conclusions are valid. And there might be an extra piece of research out there I missed.

    Anyhoo, the Neanderthal gene linked with diabetes this study identified is still being examined. Papers which explain how it influences diabetes are still being reviewed, so all I can say is that it increases the risk. Further details will have to wait until they publish this stuff

        Adam Benton · 6th February 2014 at 3:31 pm

        The gene they identify is a new one to be associated with diabetes, so there isn’t that much research on how it influences the risk for it. It seems to increase the amount of triacylglycerol in the body, which is a sign that insulin isn’t working properly. As such the Neanderthal gene may well be hampering the effectiveness of insulin, a problem which would be exacerbated with our modern diet.

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