Book excerpt: Some things are funny -- jokes, puns, sitcoms, Charlie Chaplin, The Far Side, Malvolio with his yellow garters crossed -- but why? Why does humor exist in the first place? Why do we spend so much of our time passing on amusing anecdotes, making wisecracks, watching The Simpsons? In Inside Jokes, Matthew Hurley, Daniel Dennett, and Reginald Adams offer an evolutionary and cognitive perspective. Humor, they propose, evolved out of a computational problem that arose when our long-ago ancestors were furnished with open-ended thinking. Mother Nature -- aka natural selection -- cannot just order the brain to find and fix all our time-pressured misleaps and near-misses. She has to bribe the brain with pleasure. So we find them funny. This wired-in source of pleasure has been tickled relentlessly by humorists over the centuries, and we have become addicted to the endogenous mind candy that is humor.