Life With Type 2: The Caveman's Gift

For some of us, this is how one of our great-grandfathers a thousand times removed may have appeared.

| Feb 17, 2014

The Neanderthals--Homo sapiens neanderthalensis--entered popular imagination more than 160 years ago when their remains were first discovered in Germany's Neander Valley (thal in German).

How fascinated we were at the thought that there had been another type of human, so very much like us. They were successful hunters, toolmakers, and clothes wearers who, alas, died out some 35,000 years ago.

Still, despite their closeness to us, they took a hit through the years. Based on the skeletons we found, we portrayed them as shambling, hairy, big-boned brutes. So it was easy to look down upon them as almost-men who couldn't quite compare to us. The superior skills of us agile, robust modern humans ran rings around theirs. 

But that vision slowly changed over the years as we learned more about them. Maybe they weren't quite so clumsy and unpretty. We were impressed that they buried their dead with flowers and pretty stones laid beside them, a sign that the Neanderthals were a highly intelligent people who sensed that there might be life after death.

Now we learn that in a way, they did survive death, even the death of their entire subspecies. There was an old, often-asked question about whether we and the Neanderthals ever mated, whether men and women from those different human families 60,000 or 70,000 years ago found one another attractive enough to have babies together.

They did. To this day, tens of thousands of years after the extinction of the Neanderthals, many of us walk around carrying small genetic endowments from our distant half-siblings. It's not unusual for modern people who undergo extensive genetic screening to learn that their DNA contains echoes from an old race.

And one of those genes may be partially responsible for an increased risk of type 2 diabetes in certain populations of modern humans, particularly Latin Americans.

Scientists studying a remote and recently discovered sub-group of Neanderthals, the Denisovans of Siberia, found the gene, called SLC16A11, in the Denisovan DNA. They think it was passed on, along with other Neanderthal genes, to modern humans.

Overall, about 2 percent of the genes in modern European and Asian humans are thought to be Neanderthal in origin. (No sub-Saharan Africans have such genes, strong proof that Neanderthals did not originate in or ever migrate to Africa, which is considered to be modern humans' ancestral home.)

Here's where it gets interesting: The presence of SLC16A11in certain populations also tends to confirm the theory that North America was populated primarily by migrations from Asia. It's plausible that modern humans, migrating through Siberia and heading gradually eastward to the Americas, interbred with the Denisovan Neanderthals. They subsequently carried the SLC16A11 gene into East Asia and onto the American continents.

SLC16A11 is very rare in Europeans and many Asian populations, but found in about 20 percent of East Asian populations--Chinese, Mongolians, Koreans, Japanese, Southeast Asians. Because these peoples lived close to the migration routes that led to North America, it's highly likely their ancestors interbred with humans who had picked up the Denisovan genes.

The gene is also found in up to 50 percent of sampled Latin American and Native American populations. Native Americans are thought by some to be descendants of the people who interbred with the Denisovans, while many Latin Americans have a mixed European and aboriginal American genetic heritage.

By itself the presence of SLC16A11 doesn't necessarily predict type 2. But it has a high-risk variant that scientists think increases the likelihood of developing type 2 by 25 percent in the people who carry it. That likelihood increases to 50 percent if both of a person's parents carry the higher-risk version.

Why, Oh, Why?

Why did the Neanderthals develop a gene that in modern humans would lead to diabetes?

One explanation is simple enough: The Neanderthals lived a hard and often hungry life in Ice Age Europe and Asia. Both were cold, forbidding landscapes that did not offer a lot of food for hungry humans. The Neanderthals' diet was mostly meat. Their frigid habitat did not provide abundant carbohydrates in the form of fruits or wild cereals, and Neanderthal technology simply could not have achieved the food breakthrough that the invention of agriculture 25,000 years later gave modern humans.

In the Neanderthals' world, abundant carbohydrates were a rare occurrence. Their bodies never evolved to deal with too many carbs, so they never needed a means for dealing with them. That lack of an ability of handle a lot of carbs may have been passed down to us.

Even as we Homo sapiens sapiens developed agriculture, with its provision of a sure source of carbohydrates, we never had an overwhelming volume of them until modern commerce and industry were able to shower us with endless quantities of cheap refined grains and sugar. If you overwhelm our systems with a food source we're not really genetically prepared to deal with, then add a genetic component from a species that was even worse at dealing with carbs than us, you get a Double Whammy.

So, hats off to our ancient Neanderthal kin, who for many of us are, literally, our flesh and blood.

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Categories: Carbohydrates, Denisovans, Neanderthals, SLC16A11, Type 2


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