Laughing is weird. Why do we do it? Psychologists think this behavioral response serves as a signal to others by spreading positive emotions , decreasing stress and contributing to group cohesion. For those same reasons, chimps and orangutans smile and laugh during social play too. In fact, many hypothesize that laughing evolved from panting. When our prehuman ancestors wrestled playfully with each other, they got all panty... and that eventually turned into getting laughy.