At the very bottom of the human spine is a bone that sticks out a bit called the coccyx (cox-ix). We sometimes call it the “tailbone,” but it is actually made up of several different spinal bones.

In some animals that actually have tails, those different bones at the bottom of the spine help them move their tail around. But in humans, those bones partially fused together.

You may already know a thing or two about the tailbone if you’ve ever hit a big bump while sledding or you’ve fallen on your behind. It can be pretty painful. You might have even thought that a tailbone seems kind of useless for a human that doesn’t even have a tail.

I decided to ask my friend Erika Deinert about these bones in the human body. She’s a tropical biologist and adjunct professor in biological sciences at Washington State University Vancouver.

Even though your parents and grandparents didn’t have tails, if we went back in time and looked at ancestor species that we have in common with other primates, we would see some tails, Deinert explained.

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Dr. Universe