Our very ancient animal ancestors had tails. Why don't we? Somewhere around 20 million or 25 million years ago, when apes diverged from monkeys, our branch of the tree of life shed tails.

Yet, as you get closer to humans on the evolutionary tree, tails disappear. Gorillas don't have them. And neither do chimps or any other ape — including us, of course. To understand why ...

Yet, as you get closer to humans on the evolutionary tree, tails disappear. Gorillas don't have them. And neither do chimps or any other ape - including us, of course. To understand why ...