Ice Age Diabetics?

15 03 2010

Good tidings and well-wishes!

I’ve recently been greatly enjoying Sharon Moalem’s relatively new evolutionary medicine book entitled “Survival Of The Sickest: The Surprising Connections Between Disease And Longevity”. Last night, it was through this volume that,  while taking a break from homework, studying, and Godzilla movies, I came across one of the most evocative hypotheses I’ve encountered in recent memory: the idea that modern diabetes may have originally evolved as a means with which our ancestors combatted the Ice Age’s notoriously cold temperatures.

For those unfamiliar with this concept, its of critical importance to realize that sugar is a natural antifreeze which, obviously, lowers the freezing temperature of water dramatically. This is due to the fact that anything which dissolves in liquid water inhibits its ability to form solid ice crystals (in fact, finding water in a natural environment which freezes at precisely 32 degrees Farenheit is devilishly difficult, for most  water samples found in these locations contain a number of impurities).

Ice wine relies on this tendency, for as winter approaches and temperatures drop, grapes expel enormous amounts of water while virtually retaining the entirety of their individual sugar supply. Thus, they are able to prevent the growth of potentially-damadging ice crystals. My beloved upstate New York wood frogs (Rana slyvatica) employ the same strategy which, in their case, allows them to literally freeze solid during the winter. After the amphibian’s skin senses a certain drop in temperature, water is pooled into its abdomen whilst a colossal amount of glucose is dumped by the liver into the bloodstream which, combined with the release of additional sugar alcohols, increases the blood sugar’s overall presence to nearly a hundredfold.

Okay, then: how does all this relate to human diabetes? Consider the following Moalem passage:

“As a theory, it’s hotly controversial, but diabetes may have helped our European ancestors survive the sudden cold of the Younger Dryas.

As the Younger Dryas set in, any adaptation to manage the cold, no matter how disadvantageous in normal times, might have made the difference between making it to adulthood and dying young….

[I]magine that some small group of people had a different response to the cold. Faced with year-round frigid temperatures, their insulin supply slowed, allowing their blood sugar to rise somewhat. As in the wood frog, this would have lowered the freezing point of their blood. They urinated frequently, to keep internal water levels low… Suppose these people used their brown fat to burn that oversupply of sugar in their blood to create heat. Perhaps they even produced additional clotting factor to repair tissue damage caused by particularly deep cold snaps. It’s not hard to imagine that these people might have had enough of an advantage over other humans… to make it more likely that they would survive long enough to reach reproductive age.”

While this may sound highly speculative, there’s actually a decent amount of evidence to support the notion:

-The bodies of lab rats essentially become diabetic (that is, they grow resistant to their own insulin) when exposed to cold temperatures.

-More Northern Hemisphere inhabitants are diagnosed with diabetes between November and February than between June and September, theoretically due to the noticable drop in temperature during the former period.

-Almost invariably, children are diagnosed with Type 1 diabetes during the late fall as temperatures drop.

-The aforementioned clotting factor is more scientifically called ‘fibrinogen’, a substance which, in humans, reaches the height of its abundance during the winter.

-An extensive study of U.S. veterans revealed that not only do the subjects’ blood sugar levels spike while winter is at hand, but that those who hail from environments with a great deal of variation in seasonal temperature (ie: colder districts) had a particularly extreme physiological contrast in this regard.

-Food during the last Ice Age was almost certainly limited, meaning that dietary blood sugar likely followed suit. Therefore, the insulin of a diabetic from this epoch may have never come close to reaching dangerous levels.

This amazing hypothesis just goes to show that evolution does not merely pertain to the fossil record and the occasional Galapagos finch as most people seem to believe, but rather, it affects the lives of all organisms, including ourselves, in ways we can scarcely imagine.




3 responses

15 03 2010
Zachary Miller

Whoa, that’s kind of awesome! There are similar mechanisms in place to describe the modern prevalance of sickle-cell anemia and cystic fibrosis.

15 03 2010

Interesting. I read an article on Nat Geo News a little while ago that said dolphins laso have type 2 diabetes (or something like it). Difference is, apparently dolphins can turn their diabetes on and off.

15 03 2010

Hmm, I wonder how these cetaceans are able to accomplish this most intriguing feat…

And Zach, you may be interested to hear that Haemochromatosis, a disease which spreads obscene amounts of iron to sections of our bodies, may have helped many Europeans survive the black plague. This is because the plague bacteria require iron to function, which is usually obtained via white blood cells. But haemochromatosis actually RESTRICTS the amount of iron these cells acquire, meaning that the plague has a hell of a time trying to infect someone with this genetic disease. However, in a post-plague world, it’s actually become a bit of a handicap, just as diabetes has theoretically outlasted its usefulness.

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