Scientists are increasingly finding that behaviours once seen as depraved often have a direct physical cause. To find out more, Ian Sample hears from Guy Leschziner, a consultant neurologist and sleep physician at Guy’s and St Thomas’ hospital in London. His new book, Seven Deadly Sins: The Biology of Being Human, looks at the neurological basis of behaviours often dismissed as evidence of bad character or lack of willpower. Help support our independent journalism at theguardian.com/sciencepod