Re: Why is the clavicle the last of our bone's to stop growing?

The clavicle is a really ancient bone -- it's found in bony fish, where it helps support the pectoral fin. In humans, clavicles are big bones because we're descended from brachiating apes, who use the bone to transfer forces between their arms and their swinging bodies. But lots of animals have small clavicles -- and some, like dogs, have lost them altogether! In a growing human fetus, the clavicle is the first bone to start laying down calcium to become hard, a process called ossification. After birth, it grows larger the same way as other bones -- by adding cartilage to its ends and ossifying them. Clavicles don't form cartilage at the end next to the sternum until the bone is nearly finished growing, at about age 19-20 in humans. Some other bones actually stop growing later than the clavicle -- elements of the pelvis don't fully ossify until about age 22-25 in humans. No one knows why any bone adheres to a particular ossification timetable. Diane Kelly