Humans are, first and foremost, social creatures. And this, according to the authors of I'll Have What She's Having, shapes--and explains--most of our choices. We're not just blindly driven by hard-wired instincts to hunt or gather or reproduce; our decisions are based on more than "nudges" exploiting individual cognitive quirks.I'll Have What She's Having shows us how we use the brains of others to think for us and as storage space for knowledge about the world. The story zooms out from the individual to small groups to the complexities of populations. It describes, among other things, how buzzwords propagate and how ideas spread; how the swine flu scare became an epidemic; and how focused social learning by a few gets amplified as copying by the masses. It describes how ideas, behavior, and culture spread through the simple means of doing what others do.It is notoriously difficult to change behavior. For every "Yes We Can" political slogan, there are thousands of "Just Say No" buttons. I'll Have What She's Having offers a practical map to help us navigate the complex world of social behavior, an essential guide for anyone who wants to understand how people behave and how to begin to change things.