Why do humans have a tailbone?
Quick Answer
The tailbone (coccyx) is a remnant of the tail our ancestors had, and it still anchors important muscles.
The Full Story
The coccyx is made of three to five small fused vertebrae at the bottom of the spine. Human embryos briefly develop a tail around the fifth week of development, which is then reabsorbed. Our primate ancestors lost external tails roughly 25 million years ago, and a 2024 study in Nature linked the loss to a genetic change in a gene called TBXT. The tailbone is not useless: it helps support weight when sitting and is an attachment point for muscles, tendons and ligaments of the pelvic floor. It is often described as a vestigial structure because it has lost its original function.
Key Facts
YouTube Angle
Suggested video title for this topic:
"The tail you almost had — and the gene that took it away"