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Why Do Monkeys Have Tails But Humans Don’t?

Monkeys have tails for balance and agility in their arboreal habitats, aiding in climbing and communication. Humans, having evolved for bipedal locomotion, lost the need for tails. Our ancestors' shift to the savannah led to different evolutionary pressures. Intrigued by our primate cousins' tails? Consider how our paths diverged, and what it means for our understanding of evolution. What else might we uncover?

This is the tale of a single gene mutation. Actually, it's about a single gene mutation and the tail. As you know, when you look behind you, you don't see a tail dragging along the ground. Our great ape relatives, such chimpanzees, orangutans, and gorillas, don't have tails either, yet monkeys do. Perhaps you've never wondered why.

Geneticist Bo Xia has. He thought about it as a kid, but it really came to the forefront when he injured his coccyx in a car accident. Xia and other researchers began looking into the genetic basis for the tail. Much to their surprise, they found that the difference is a single gene mutation. To put it simply, the crux of their finding is that at some point in the past, altering that gene provided a survival advantage.

A single gene mutation could be responsible for why monkeys have tails, but great apes (including humans) do not.
A single gene mutation could be responsible for why monkeys have tails, but great apes (including humans) do not.

"For something to be lost in one big burst is really significant, because you don’t then have to posit millions of years of successive tiny changes accumulating gradually,” said Carol Ward of the University of Missouri. Now Xia and his team hope to learn what specific advantage the mutation provided.

Some de-tails:

  • An alpha dog raises its tail high in order to mark its territory, while submissive dogs keep their tails between their legs.

  • The only monkeys that have prehensile (grasping) tails are New World monkeys, like spider and howler monkeys.

  • If a cat holds its tail up, it's happy; if the tip shakes a little, the cat is really pleased. A twitching tail, on the other hand, means "leave me alone."

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    • A single gene mutation could be responsible for why monkeys have tails, but great apes (including humans) do not.
      By: Rafael Saldaña
      A single gene mutation could be responsible for why monkeys have tails, but great apes (including humans) do not.