We all know what love is. Or at least we think we do. But why do we fall in love? What actually goes on in our brains when we love someone? What does "chemistry" really mean for the way we approach relationships? In this day and age we want our advice backed by cold, hard science. Instead of Mom's shoulder, Freud's couch or the pastor's office, we often look for answers in genetic profiles and brain scanners. Today's guest has investigated the latest findings in biology, neuroimaging, endocrinology, evolutionary science, psychology and more to gain insight into why we do what we do when we're in love.