According to the research, people whose smiles were weakest in snapshots from childhood through young adulthood were most likely to report being divorced in middle and old age. Among the weakest smilers in college photographs, one in four ended up divorcing, compared with one in 20 of the widest smilers. The same pattern held among even those pictured at an average age of 10…

The scientists speculate that one’s tendency to grin—an example of what psychologists call “thin slices” of behavior that can belie personal traits—reflects his or her underlying emotional disposition.