It’s the closest we ever come, as humans, to a transformation as profound as that from a caterpillar into a butterfly. In the first two months of our existence, each of us changed from a single egg to a flat disc, to a hollow tube, to a little creature with stumpy arms and legs, to something that looked recognisably human. And in the course of that embryological development, there were echoes of earlier stages of evolution, harking back to very ancient ancestors - ancestors we share with living insects, fish, amphibians and reptiles.

The story of how a human body develops, from a single cell to a complex organism, is - Alice Roberts argues - the most fascinating narrative that science has to offer us.