为什么大象毛发稀少?

Hair helps keep you warm, right? But hair can also keep you cooler than bare skin, as long as the hair is not too thick. So says a study in the journal PLoS ONE. [Conor L. Myhrvold, Howard A. Stone and Elie Bou-Zeid, What Is the Use of Elephant Hair?]

Researchers studied elephants, which have very thin coats of hair. It's easy for the beasts to overheat: they may face temperatures of up to 120 degrees Fahrenheit, and they don't have much skin surface area to radiate the heat relative to their big body volume.

That's where the hair comes in. The researchers wrote equations modeling the elephants' hairy skin. As they expected, thick hair traps air and keeps the body warm. But below a certain density, hair stops insulating and wicks heat off the body instead—helping the elephants get rid of an extra 20 percent of their body heat, especially on windless days.

Heat sinks inside computers work in a similar way, with pins sticking up to help dissipate the interior heat.

The researchers speculate that hair may have actually evolved to help animals stay cool, because it first sprouted in mammals over a hundred million years ago in a hot climate. Hair-raising times, indeed.

—Christopher Intagliata