Babies are born with about 300 bones, but adults end up with only 206.

A newborn’s skeleton contains around 270 to 300 separate bony and cartilaginous pieces, many of them still soft cartilage rather than fully hardened bone. As a child grows, dozens of these smaller pieces gradually fuse together into single, larger bones — the skull alone starts as several separate plates that knit together over the first couple of years of life.

By adulthood, that fusing process leaves a fixed count of 206 bones in the typical human skeleton. The extra bones and cartilage in infancy aren’t wasted; the flexibility they provide is essential for a baby to pass safely through the birth canal, and it gives the growing skeleton room to lengthen and reshape as the child develops.