You have a mind, right? At least, that's what you and those who know you will think. But would you say the same of your pet? What about creatures like dolphins or octopus? Aliens (assuming they exist)? Robots and AI? God? What does it mean to 'have a mind'? Are all minds the same? Why should such a costly thing appear in evolution? And if we understand our minds, does that mean we have finally understood ourselves? In this week's episode, Nick Spencer speaks to science writer Philip Ball about his book The Book of Minds: Understanding Ourselves and Other Beings, From Animals to Aliens.