The third episode looks at anxiety and explores why it is so common. It talks to neuroscientists who explain the physiological and evolutionary basis of anxiety. Although it can help animals escape predators, anxiety can cause serious problems for human beings. It talks to sufferers of anxiety and examines the different types of anxiety people can feel. It also looks at how social media can cause anxiety.

The final episode of this series looks at what happens to the brain when someone uses psychedelic drugs. It looks at how psychedelic drugs may be useful in dealing with anxiety in cancer survivors and serious depression. It explores the history of psychedelics and examines early medical experimentation with the drug. It also discussed why psychedelics were banned and examines how they affect the brain.

The polar regions of our planet may seem beyond the reach of most of us, but they are not beyond our influence. We, unintentionally, are changing these frozen worlds, and these changes will not just affect the poles but the whole planet. On the unforgiving frontier of climate change, polar bears, walruses, seals and penguins find their icy Edens in peril.

A fifth of the land on our planet is covered by desert. Deserts may appear to be barren and empty, but they are of crucial importance to life. For those that can overcome their challenges they provide a vital refuge. The Grasslands are one of our planet's most productive landscapes. They support the greatest aggregations of large animals on Earth. Cameras follow desert elephants seeking sustenance, bison roaming North American grasslands and caterpillars living the good life underground.

Everything that lives on land, animal or plant, depends on fresh water. Yet only part of it is within reach: Much of the planet's fresh water, is locked away, almost two-thirds of it lies frozen around the poles. Even away from the poles, much of the land's fresh water freezes each winter. The need for fresh water is as strong as ever. However, the supply is becoming increasingly unpredictable and uncertain for all manner of species. We are not alone in our need for water, but we have the ability to ensure the fresh waters of the world do flow, and we alone can determine how they are shared.

We will see in this episode how Scottie Pippen rises from obscurity to become one of the NBA's best players. Also how an injury early in Michael Jordan's career sows distrust with Chicago Bulls management. Scottie Pippen took an unusual path to the NBA, growing into a star at Central Arkansas. Pippen earns the trust of Jordan and finds the perfect role as an elite wing defender and playmaker, but his frustration with management over his contract leads to a trade demand in 1997.