You started life as a single cell. Now you are made of many trillions. There are more cells in your body than there are stars in the galaxy. Every day billions of these cells are replaced. And if you hurt yourself, billions more cells spring up to repair broken blood vessels and make new skin, muscle or even bone.rnEven more amazing than the staggering number of cells, though, is the fact that, by and large, they all know what to do - whether to become skin or bone and so on. The question is, how?
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