Historical story

When did man lose his tail?

The editors of Kennislink regularly receive questions from readers. For example, a reader wondered when man lost his tail, and what the last humanoids were that still had a tail.

Humans, unlike most other vertebrates, do not have a tail. This has not always been the case. Our ancestors, the ape-like primates, did have tails until about 20 million years ago. A dominant mutation whose frequency has been increasing is to blame for the disappearance of our tails. It is impossible to say with certainty why this path has evolved. There is, however, a dominant theory about the disappearance of the human tail.

However, the most plausible theory about this is that because our ancestors were relatively heavy compared to other vertebrates, the tail lost its function as a stabilizer. In smaller apes, the tail can function as a stabilizer, allowing them to move quickly high in trees, for example, without losing their balance. At one point our ancestors simply became too heavy to take advantage of their tails, so evolution made them disappear. This would also explain why other (also relatively heavy) great apes such as gorillas, orangutans and chimpanzees no longer have a tail.

You can still see from the human skeleton that our ancestors did have tails. Humans have four small tail vertebrae (also called sosyx) in the lower back. Although this no longer fulfills the function of a stabilizer, it is not completely useless, because muscle tissue from, among other things, the large buttock muscle is attached to it.

Yet every year people are still born with a tail. In most cases, these tails have muscle and bone tissue. People with such a tail can even move it. About a third of all human tails fall under the so-called pseudo-tails. A pseudo-tail is basically a deformity on the lower back that resembles a tail. Such tails are often removed shortly after birth.