Professor Marcus du Sautoy goes in search of answers to one of science's greatest mysteries: how do we know who we are? While the thoughts that make us feel as though we know ourselves are easy to experience, they are notoriously difficult to explain. So, in order to find out where they come from, Marcus subjects himself to a series of probing experiments.
Kate Humble journeys to the far north of Siberia in the teeth of the Arctic winter to travel with the Nenets. These reindeer herders spend their lives migrating with the seasons up and down the Yamal Peninsula, following their herds from pasture to pasture. But it's a tough and precarious existence, living in temperatures that can drop to -54C. And the extremes soon take a toll on Kate - a lover of warm weather - and her crew, when on the way to meet their Nenets family their vehicle breaks down and they're forced to abandon their plans.