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One-third of the earth's surface is classified as desert. The writer William Atkins has travelled to eight of the world's hottest, driest places. He tells Andrew Marr about these forbidding, inhuman landscapes. The Arabian Desert lies mostly in Saudi Arabia but crosses borders from Egypt to Qatar, UAE to Oman. The economic analyst Jane Kinninmont looks at how this shared landscape affects regional politics and culture.In the 1950s deserts were the preferred places for Britain and America to test their nuclear bombs in secret. The science journalist Fred Pearce explores the human ingenuity - and human error - that has fuelled the atomic age. Producer: Katy Hickman.

Psychedelic drugs are once again being trialled to treat a range of psychological conditions. The writer Mike Pollan tells Kirsty Wark about the science of LSD and magic mushrooms: from the 1940s to the 1960s they promised to shed light not only on the deep mysteries of consciousness, but also to offer relief from addiction and mental illness. Banned since the 1970s, there is now a resurgence of research into these mind-altering substances.While some psychiatrists were getting their patients to experiment with psychedelics in the 1950s, far more were administering electroconvulsive therapy - both have a controversial history. ECT involves sending an electric current through the brain to trigger an epileptic seizure. It gained a reputation as a barbaric treatment, after the film One Flew Over The Cuckoo's Nest. But the psychiatrist Dr Tammy Burmeister believes that it's time people understood the therapeutic potential from this procedure.The poet Andrew Motion's latest book Essex Clay is an attempt to return to heartfelt memories of childhood. He looks back at his mother's riding accident, which left her 'floating herself among the nebulae and gas clouds of her vast unconsciousness' and her subsequent slow death. The book revolves around loss and memory and retrieval. The evolution of the human brain is one of the wonders of nature, but the philosopher of science Peter Godfrey-Smith asks what if intelligent life on Earth evolved not once, but twice? He wonders how the octopus - a solitary creature - became so smart. He traces the story from single-celled organism 3.8 billion years ago to the development of cephalopod consciousness, casting new light on the octopus mind. Producer: Katy Hickman.

Booker Prize-winning novelist Arundhati Roy's latest book weaves together the lives of the misfits and outcasts from India's bustling streets. Roy is famous as an advocate for the most vulnerable and dehumanised in Indian society. She tells Andrew Marr how her main character Anjum builds a small paradise for the dispossessed in a graveyard in Delhi. Ivan Mishukov walked out of his Moscow flat aged four and spent two years living on the city streets, where he found a home among a pack of wild dogs. Playwright Hattie Naylor used this true and extraordinary story as the basis for a play and now a film, Lek and the Dogs. She explores how the human world failed to look after the child, but how his kindness won the trust and protection of street dogs.Damian Le Bas grew up surrounded by Gypsy history from his great grandmother. He sets out on the road to discover Travellers' stopping places and to understand how the romanticised stories of the past were replaced by the critical, outcast image of present-day Gypsies.The columnist and Conservative Peer Daniel Finkelstein appears to be the ultimate establishment insider. But his parents were refugees who were forced to move across Europe because of antisemitism. He believes their desire for rootedness and belonging underlines his own politics.Producer: Katy HickmanPicture: Arundhati Roy (credit Mayank Austen Soofi).