Newborn babies have 300 bones (by age 5 the amount of bones merges to 206).
It may be difficult to imagine when looking at a tiny newborn baby, but that infant has around 300 bones — and those bones are growing and changing shape every day.
Adults, on the other hand, have 206 bones, which make up about 15 percent of their body weight.
Wait — did we really just say that babies have nearly 100 more bones than adults? How is that possible?
Well, even though bones appear to be tough and rigid, they’re actually made up of living tissue and calcium that’s always being built up and discarded throughout your life.
As your baby grows into childhood, much of that cartilage will be replaced by actual bone. But something else happens, which explains why 300 bones at birth become 206 bones by adulthood.
Many of your baby’s bones will fuse together, which means the actual number of bones will decrease. The space that separates the ends of two bones that eventually fuse is also cartilage, like the tissue you have in the tip of your nose.
The fusing of bones occurs throughout the body. You may notice that there are one or more soft spaces in between the bones in your baby’s skull. These “soft spots” may even freak you out a bit, but they’re perfectly normal. They’re called fontanelles, and they’ll eventually close as bones grow together.
Replacing cartilage with fused bone begins when tiny blood vessels — called capillaries — deliver nutrient-rich blood to osteoblasts, the cells that form bones. Osteoblasts create bone that covers cartilage at first and then ultimately replaces it.