Friends matter to us, and they matter more than we think. The single most surprising fact to emerge out of the medical literature over the last decade or so has been that the number and quality of the friendships we have has a bigger influence on our happiness, health and even mortality risk than anything else except giving up smoking. In Friends, psychologist Robin Dunbar looks at the way different types of friendship and family relationships intersect and at the complex of psychological and behavioral mechanisms that underpin friendships and make them possible – and just how complicated the business of making and keeping friends actually is.