They had known each other since eighth grade, sharing the silly private jokes that only longtime pals know. Later, they lost touch for a couple of years, when they went to different colleges. But in their senior year the friendsnow a young man and womanbecame inseparable whenever they were home visiting their families. One evening just after graduation, when he dropped her off at her house in his old green pickup truck, he leaned over and kissed her. He found himself speechless for long moments afterward. She felt a shivery thrill as everything about their comfortable old relationship suddenly seemed to change. A month later he would propose.

My old friend and I have now been married for 18 years, but I remember that moment with crystal clarity. As Chip Walters feature article, Affairs of the Lips, explains, a smooch can communicate in powerful ways that spoken language does not easily match. Kisses, Walter writes, can convey important information about the status and future of a relationship. A bad first kiss, too, can bring an otherwise promising beginning to a quick close.

Too much emotion can cloud judgment, particularly when matters turn from deciding about personal attachments to coping with challenging moral questions. Imagine that a runaway trolley will strike five unsuspecting workers around a bend in the tracks ahead. Could you push a stranger in front of the trolley to save the workers? Cold logic might dictate trading one life for fivebut would that be right? In When Morality Is Hard to Like, Jorge Moll and Ricardo de Oliveira-Souza discuss the cognition of morality.

Having a solid relationship or knowing you made the best decision in a bad spot cannot completely shield you from lifes stresses. As Turhan Canli writes in The Character Code, understanding an anxiety gene could ease suffering for those with mood disordersand give us yet another important clue about the whys behind our shared human experience.