Over your lifetime you undergo an extraordinary change - no other animal on earth goes through such a dramatic metamorphosis. In this programme, Chris and Xand van Tulleken explore the latest understanding of how we all grow. They uncover the reason our childhood is longer than any other creature on Earth and reveal the communities of microbes - our microbiome - that we cultivate throughout our lives. They uncover the mysterious trigger for our transformation from child to adult and, for the first time, show the remarkable spark of life that is emitted when sperm and egg first meet.