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 ofhow 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.

Drs Chris and Xand van Tulleken discover the everyday miracles that keep you alive. They explore the extraordinary lengths our bodies go to in order to keep our organs working at every moment of every day. They see how powerful reflexes keep us safe from danger and uncover the amazing mechanisms our bodies call on to repair damage. And for the first time ever, they see exactly how our immune systems’ killer cells go into battle against deadly infection.

This episode explores the way our experiences shape our minds and bodies as we make the journey from the most helpless to the most sophisticated organism on earth. Dr Chris and Dr Xand van Tullekan uncover how we develop new skills - whether riding a bike or learning to walk.