Michael Mosley explores the latest science about how our personalities are created - and whether they can be changed. 　　Despite appearances, Mosley is a pessimist who constantly frets about the future. He wants to worry less and become more of an optimist. 　　He tries out two techniques to change this aspect of his personality - with surprising results. 　　And he travels to the frontiers of genetics and neuroscience to find out about the forces that shape all our personalities.