One of the greatest conundrums of life is how we emerge from a single cell into a walking, talking, multi-trillion-celled organism that we call the human body. In the first of this year's Christmas Lectures, Dr Alison Woollard from the University of Oxford reveals just how this incredible transformation takes place. Using dramatic live experiments she shows how each of those trillions of cells knows what to do, when to do it and how to organise themselves to carry out vital specialist roles in our body.