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What's the Point of Elephant Hair?

By Alex B. Berezow

Elephants have hair. Why? It's not like they need it to keep warm, considering they live in Asian jungles or on the African savanna. A biologist might say that hair is vestigial -- a sort of evolutionary leftover from whatever mammalian ancestor required hair to survive, probably because it needed to stay warm.

Not so, say Princeton University physicists and engineers in the journal PLOS ONE. They believe elephant body hair plays a very important role in thermoregulation, specifically in dissipating heat. Elephants are bulky, having the greatest volume-to-surface-area ratio of any land mammal. In other words, they have a big, hot body with relatively little skin to eliminate that heat. That's why they usually flap their ears and throw dirt and water on themselves; that's how they cool off.

But, that's not all. According to the researchers, the hairs that line the body of the elephant are involved in conductive heat transfer. (See figure.)

Using a computer model, the researchers showed that hair helps conduct heat away from the elephant. The X-axis represents air velocity (i.e., how windy it is outside), and the Y-axis represents heat transfer. As shown, when it is not windy (air velocity near zero), having more hair is beneficial to the elephant because it can eliminate more waste heat. However, hair becomes less important as it becomes windier.

Perhaps elephant hair isn't just a pointless leftover from evolution. Indeed, it may be one of the reasons why elephants can survive in hot climates.

Source: Myhrvold CL, Stone HA, Bou-Zeid E (2012) What Is the Use of Elephant Hair? PLoS ONE 7(10): e47018. doi:10.1371/journal.pone.0047018

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