We humans are a bit of an oddity in lacking a tail. It’s only really the apes, among vertebrates, that have dispensed with a posterior extension of the spinal column.
All that remains of our tail is the coccyx, the only function of which is apparently to hurt very much when someone pulls a chair from beneath us as we go to sit down. But why don't humans have tails? Let's explore.
Do all vertebrates have tails?
Although most vertebrates have tails, there are a few notable exceptions. Humans and great apes are two such exceptions, along with frogs and toads.
As tadpoles, frogs have tails – but these are later reabsorbed back into their bodies. You might be surprised to hear that something similar actually happens with humans…
- Why do some frogs have five legs?
- Are humans really descended from fish?
- How many times could a lizard regrow its tail?
Why don't humans have tails?
It’s not entirely known why we apes lost our tails, though it may relate to a change in locomotion style when our ancestors descended from the trees.
There was a genetic mutation about 25 million years ago in the TBXT gene, which is specifically related to tail development. This led to the loss of tails in humans and other apes.
Interestingly, however, human embryos develop a tail-like structure – essentially, an extension of the spine – in the first few weeks of development. This is reabsorbed into the body by around the eighth week, going on to form the coccyx (tailbone) at the very base of the spine. This is a callback to our evolutionary past, when early primates had tails.
