In May 2005 Penguin will publish 70 unique titles to celebrate the company's 70th birthday. The titles in the Pocket Penguins series are emblematic of the renowned breadth of quality of the Penguin list and will hark back to Penguin founder Allen Lane's vision of 'good books for all'. Award-winning writer and psychologist Steven Pinker has continually shown that provocative, complex ideas can be translated into bestsellers. In this extract from How the Mind Works he takes us deep into the human psyche as he considers people's desire for happiness, the power of the emotions and how love can come to conquer all.