Discover the science of social circles with Professor Robin Dunbar, creator of Dunbar's Number (the 150-person limit for friends and family). Uncover the distinct layers of friendship, from the inner core of five "shoulders to cry on" to the 15-person sympathy group and the 50-person "weekend barbecue" layer. Learn the shocking truth about how much time investment (up to 200 hours for new close friends) is required to move someone from an acquaintance to your inner circle. Professor Dunbar reveals the role of homophily (similarity), the seven pillars of friendship, and the ultimate icebreaker: singing. Don't miss this essential guide to understanding, building, and maintaining your most important relationships.