You were born with more bones than you have now

An adult human skeleton has roughly 206 bones — but you started with far more. Infants are born with about 270 separate bones, and as the skeleton matures many of them fuse together, settling near the familiar adult count.

The skull shows this best. A baby’s cranium arrives in separate plates with soft gaps (fontanelles) between them, letting the head flex during birth and the brain grow fast afterward. Those plates knit into a solid vault over the first years of life. The spine’s sacrum and the tailbone (coccyx) likewise begin as multiple pieces that merge.

Even the “206” is approximate — sources put the adult range at roughly 206 to 213, because some people carry extra small sesamoid bones.

So the skeleton isn’t a fixed scaffold you simply grow into. It’s a structure that actively consolidates, trading the flexibility a developing body needs for the rigidity an adult one relies on.