Hot or Cold? The Science Behind Body Temperature

Winter is upon us: the days are short, the temperatures have dropped, and in many parts of the country, ski season is in full swing. It’s time to unpack puffy jackets and fleece hats and start layering. In the winter, I wear a lot of layers, but even that doesn’t guarantee that I won’t still be shivering from now until March. Am I layering improperly or failing to consume enough calories? Recent research suggests that the answer to staying warm in cold weather (or remaining cool during the summer) may actually be in our genes.

When early humans left the middle of the earth ventured to different parts of the globe, they encountered vastly different climates. In 2002, human geneticist Douglas Wallace presented research that suggests specific mutations in the mitochondria helped humans adapt to living in these new climates because it gave them the ability to stay warm in cold weather or cool in hot climes.

The Cliffsnotes explanation of body heat is simple: as the mitochondria (the body’s power house) exchange electrons, a certain amount of energy is lost and then converted into body heat. The amount of calories used for work and for heat is kept in careful balance, one that can be altered by the efficiency of the mitochondria. Basically, inefficient mitochondria lose more energy and the more energy that is lost, the more heat your body produces. To stay warm in cold weather, you want inefficient mitochondria.

In his initial study, Wallace discovered that people from cold climates have a variation in their DNA that makes their mitochondria less efficient. He discovered a different mutation in people who originated in hot climates, one that made their mitochondria more efficient (better for staying cool in hot places). People from temperate areas had a mutation that produced an intermediate metabolism. Although the sample size was small, Wallace’s work suggests that humans didn’t just adapt their behavior to the new environment, their DNA adapted as well.

This isn’t to say that people should live in a climate that suits their metabolism. The human body is capable of making micro adjustments in a short period of time–like acclimatizing to hiking in the heat of the summer or to Nordic skiing in sub-zero temperatures. Layering and eating calorie-rich foods are easy ways to crank up your internal heat, while wearing light-colored cotton clothes during the summer makes the heat more bearable. But, if you’re curious about the climate your ancestor’s may have adapted to, genetic companies like 23andMe can locate these variations in your mitochondria.