You were born with more bones than you have now

A newborn has around three hundred bones; an adult, two hundred and six. The numbers don't add up, for a lovely reason: you don't lose them, they fuse.

Many of a baby's bones aren't pure bone yet, but soft, more flexible cartilage. That softness makes sense: it eases the incredibly tight journey through the birth canal and leaves room to grow. The skull, for instance, arrives in several plates separated by gaps, the fontanelles, that soft spot on the head that feels so nerve-wracking to touch.

Over the years, those pieces harden and weld together. The skull bones close, the vertebrae of the sacrum join into one, and the count drops to two hundred and six.

So growing up isn't just getting bigger: it's literally putting the pieces together.