People who lived in the Arctic thousands of years ago ate fatty marine mammals almost exclusively. It's impossible to plant crops in the frozen ground, and not much grows. So, sometime between 23,000 and 6,000 years ago, humans who lived there began to evolve — they developed a tolerance to the cold and to the high-fat diet, including high blood pressure and high metabolic rate.

Now, those adaptations that once kept people alive in one of the world's most forbidding environments is killing them today, according to findings published Thursday in the American Journal of Human Genetics. The genetic advantage of the past is at the root of higher-than-normal infant death and hypoglycemia in today's Arctic populations. "Evolutionary impacts on health might be more prevalent than currently appreciated," wrote the authors, lead by Dr. Florian Clemente, of the University of Cambridge.

In Siberia, they said, temperatures can drop to minus 94 degrees. The scientists dove into the genomes of 25 people from Northern Siberia, 25 from Europe, and 11 from East Asia. They were looking for gene variations that have arisen in the vastly different climates. They identified one "that was unique to Northern Siberians," located in a DNA strand that orders the production of enzymes that digest long fatty acids, according to a news release on the finding. Long fatty acids are "prevalent in meat-based diets."

Previous research has uncovered an association between this same genetic variation and "high infant mortality and hypoglycemia in Canadian Inuits." This isn't the only beneficial adaptation that has outlived its usefulness in modern humans. Our craving for donuts and Big Macs now is the result of fat and sugar scarcity in early humans, which has led to obesity, heart disease, and an entire industry for diet pills. But doctors now have no doubt there will be more finds like these. "The study's results illustrate the medical importance of having an evolutionary understanding of our past," Clemente said.

Source: Clemente F, et al. A selective sweep on a deleterious mutation in the CPT1A gene in Arctic populations. American Journal of Human Genetics. 2014.