The Tail You Kept After Losing The Tail

The human tailbone, or coccyx, is far from a useless evolutionary remnant. While we lost our external tails millions of years ago, we kept the foundation to prevent our internal organs from falling out of our bodies.

This small, triangular bone serves as a critical anchor for a network of muscles, tendons, and ligaments. These tissues form a hammock-like structure known as the pelvic floor. Without the tailbone to tether these muscles, the weight of your gut and bladder would have no support while you stand upright.

It also acts as the third leg of a tripod when you sit down. As you lean back, your weight shifts from your pelvic bones to the coccyx, providing stability and balance. It is a weight-bearing structure that adjusts its angle as you change positions.

Every human begins life with a literal tail. Between four and five weeks of gestation, a human embryo has a tail consisting of ten to twelve vertebrae. By the eighth week, most of these vertebrae fuse and are absorbed back into the body to form the coccyx.

Rarely, the genetic signal to stop tail growth fails, and babies are born with a true vestigial tail that even contains muscle and nerves.