https://evolution.berkeley.edu/evol...140204_diabetes

Excerpt: Last month, scientists announced that they'd discovered a gene that helps explain the difference in diabetes risk among many populations. In a strange twist, the gene version in question traces its ancestry back to Neanderthals! What exactly is going on here?

Where's the evolution?
To understand the evolutionary back story, you first need to know a little about the gene itself. The gene in question encodes a protein that helps move certain lipids into liver cells. The diabetes-contributing version of this gene differs from the standard gene version by five mutations—and these seem to alter the function of the protein enough to increase diabetes risk. Carriers of the mutated version of the gene are more likely to get diabetes at a younger age and with a lower degree of obesity than non-carriers.

Anyone can carry this gene—but the new research found that it is more common in some populations than others. Among people with many Native American ancestors, the likelihood of carrying at least one copy of the mutated gene is greater than 50%. Among East Asians, the frequency is about 10%. Among people with mainly European ancestors, the gene version is extremely rare, and it seems to be not present at all in Africans. Because people from Mexico and Latin America are much more likely to have Native American ancestry, they are also much more likely to carry this gene version, and hence, have higher odds of developing diabetes.

Through recent advances in recovering DNA from ancient bones, the genomes of several Neanderthal individuals have been reconstructed. The researchers searched through the DNA sequences of these samples and found what they were looking for. One of the Neanderthals (a newer fossil discovery from Denisova Cave) carried the diabetes-linked sequence! It seems that this gene version, now common among people of Native American ancestry, is a relic from the period of our history when humans walked the earth alongside other hominids.

This discovery does not mean that people of Native American descent (or for that matter anyone who carries the diabetes gene version) are particularly closely related to Neanderthals. Human populations from all over the world seem to have similar degrees of Neanderthal ancestry (between 1 and 4%); we all just carry different subsets of Neanderthal-derived genes—that is, unless your ancestors are from sub-Saharan Africa, where many people have no Neanderthal ancestry at all.

Neither does this discovery mean that Neanderthals had diabetes. Type 2 diabetes is a disease of the modern world, borne of a mismatch between modern, unhealthy lifestyles and a metabolism that, for the vast majority of our evolutionary history, existed in an environment where food was relatively scarce and lots of physical activity was necessary to survive. In that harsh environment, even individuals carrying genes that contribute to diabetes when food is plentiful and sedentary lifestyles are common are unlikely to develop diabetes. This helps explain how such genes can be common today. At no point in our evolutionary history have they been exposed to the rigors of natural selection. Only recently have such genes become detrimental to human health!

This discovery highlights the importance of evolutionary history in understanding and improving human health. Even the deepest roots of our past, which lead back to Africa and to our common ancestors with other, now-extinct hominid species, may become relevant at your next doctor's appointment. And we are just beginning to understand these ramifications. Advances in DNA technology have only recently allowed us to study the intersections between ancient DNA, large-scale genomic data, and modern epidemiology. So stay tuned to learn more about the results of these exciting investigations!