Why do bits of my kids grow at different rates?

Diana - Genetics is probably a major determinant. Certainly, I was disappointed when I didn't grow quite as tall as my sister who has a different father who's obviously taller. There's also a nutritional element to it. If you've got lots of protein and good vitamins, and all that stuff in your diet then you're going to grow a bit taller. Disease actually can affect how tall you end up as an adult, especially if you have some major disease during your childhood. So, one of the things that we find in archaeology is that when people started farming and living in very built up environments next to each other, they got more diseases, and their heights actually reduced whereas the hunter gatherers wandering around a few thousand years before were quite a bit taller and healthier. There is gender as well; girls generally don't tend to get as tall as men.

Chris - So there's a combination of availability of food and the interaction of your environment with your genes, but also, genes control your body at the level of individual tissues developing a different rate. Your body puts itself together in the right order so that you're growing at the right rate to support the right size frame. So, your liver and heart don't turn into an adult liver and heart, for instance, in a very young baby, everything grows at the right rate and that at the end of the day is going to be programmed by genes too.

Diana - And there's also the question of when your bones fuse because that's one of the things that the archaeologists look at. The collar bone is actually the very last bone to fuse and that's when you're 25. And presumably, you should've finished growing, but actually, your bones haven't finished growing technically until then.