Our species, it appears, is hardwired to get things wrong in myriad different ways. Why did recipients of a loan offer accept a higher rate of interest when a pretty woman's face was printed on the flyer? Why did one poll on immigration find the most despised aliens were ones from a group that did not exist? What made four of the Air Force's best pilots fly their planes, in formation, straight into the ground? Why does giving someone power make him more likely to chew with his mouth open and pick his nose? And why is your sister going out with that biker dude?

In fact, our cognitive, logical, and romantic failures may be a fair price for our extraordinary success as a species - they are the necessary cost of our adaptability. Michael and Ellen Kaplan swoop effortlessly across neurochemistry, behavioral economics, and evolutionary biology, among other disciplines, to answer, with both clarity and wit, the questions above and larger ones about what it means to be human.

NOTE: Some changes to the original text have been made with the authors' approval.