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Hair isn't just for looks. The hair on our heads keeps us warm and protects against the sun's harmful ultraviolet rays, while that growing in our noses keeps out dust and other unwanted intruders. But what about the hair on some people's knuckles?

"Generally speaking, we don't know," said John Hawks, a biological anthropologist at the University of Wisconsin-Madison.

One explanation, Hawks said, is that it's hair leftover from evolution: Our ancestor apes were covered with hair, and we are left with the small patches that seem to have persisted through the weeding out of natural selection.

But knuckle hair is a bit mysterious because other surviving patches have a purpose. For example, the hair strips we call eyebrows protect our eyes from dust and sweat. Knuckle hair, on the other hand, appears to be useless.

"There is some literature on 'mid-digital hair,' which is when a person has hair on the middle segments of the fingers," Hawks told Life's Little Mysteries. This trait is inherited from your parents and is encoded by a dominant gene , which means that you have a 50-percent chance of getting it if your mom or dad sports hair on his or her fingers.

If you're hoping to get rid of the hair on your knuckles, go ahead and shave it, as you will likely not miss it.

Got a question? Email it to Life's Little Mysteries and we'll try to answer it. Due to the volume of questions, we unfortunately can't reply individually, but we will publish answers to the most intriguing questions, so check back soon.