The last episode in the series examines how humans perceive and experience time, investigating the internal body clock which tells people when to eat, drink, sleep and relax. The importance of accurately measuring time is explored in relation to human evolution, and there's a debate about whether mankind will ever be able to travel between past, present and future.
Death is life's greatest certainty. But that may be about to change. Scientists have discovered an immortal animal that may hold the secret of endless regeneration. They're on the brink of editing our DNA so that we can cure death like a disease. Or is dying necessary for the survival of our species?