Dr Alice Roberts re-traces the greatest ever journey taken by our ancestors. Thousands of years ago one small group of our species, Homo sapiens, crossed out of Africa and into the unknown. Their descendants faced baking deserts, sweat-soaked jungles and frozen wildernesses and risked everything on the vast empty ocean. Within 60,000 years they colonised the whole world... How did they do it? Why do we, their descendants all look so different?

Horizon uncovers the secret world of our dreams. In a series of cutting-edge experiments and personal stories, we go in search of the science behind this most enduring mystery and ask: where do dreams come from? Do they have meaning? And ultimately, why do we dream? What the film reveals is that much of what we thought we knew no longer stands true. Dreams are not simply wild imaginings but play a significant part in all our lives as they have an impact on our memories, the ability to learn, and our mental health. Most surprisingly, we find nightmares, too, are beneficial and may even explain the survival of our species.

It sounds like a Hollywood blockbuster: a deadly asteroid is on a collision course with Earth. But in reality, it's only a matter of time before a giant space rock threatens to wipe out civilization. An asteroid took out the dinosaurs sixty-five million years ago. Are we next? This episode analyzes the threat and explores the many ways--from a nuclear bomb to ingenious new technology--that experts are proposing to stop Armageddon

The Shock Doctrine is a devastating critique of the free market policies which have come to dominate the world. Using shock therapy as a metaphor, the film investigates Klein's central idea of disaster capitalism. Naomi Klein's explores how both natural and man-made disasters are used to force disadvantageous political and economic changes on unwilling governments is brought to the screen in this documentary. The Shock Doctrine explores how the United States, with the help of the C.I.A., became enamored of Milton Friedman's interpretation of free-market capitalism and attempted to persuade developing nations of its value.

David Attenborough asks three key questions: how and why did Darwin come up with his theory of evolution? Why do we think he was right? And why is it more important now than ever before? David starts his journey in Darwin's home at Down House in Kent, where Darwin worried and puzzled over the origins of life. David goes back to his roots in Leicestershire, where he hunted for fossils as a child, and where another schoolboy unearthed a significant find in the 1950s. And he revisits Cambridge University, where both he and Darwin studied, and where many years later the DNA double helix was discovered, providing the foundations for genetics. At the end of his journey in the Natural History Museum in London, David concludes that Darwin's great insight revolutionised the way in which we see the world. We now understand why there are so many different species, and why they are distributed in the way they are. But above all, Darwin has shown us that we are not set apart from the natural world, and do not have dominion over it. We are subject to its laws and processes, as are all other animals on earth to which, indeed, we are related.

Cannabis is the world's favourite drug, but also one of the least understood. Can cannabis cause schizophrenia? Is it addictive? Can it lead you on to harder drugs? Or is it simply a herb, an undervalued medicine? Addiction specialist Dr John Marsden discovers that modern science is finally beginning to find answers to these questions. John traces the cannabis plants' birthplace in Kazakhstan; finds the origins of our sensitivity to cannabis in the simple sea squirt; and finds out just what it does to our brains. He meets people who have been changed by this drug in drastically different ways - from those whose lives have been shattered to those who lives have been revived.