Paul Bisceglio flags a study that explains how we evolved to distinguish between genuine and feigned laughter:
Genuine laughs are produced by an emotional vocal system that humans share with all primates,” [Gregory] Bryant says in a press release. This system seems to have really strong control over our windpipes, so it allows us to shoot out quicker breaths of air when we laugh for real than when we fake it. We laugh faster as a result.
This speed difference between real and fake laughter is subtle, but not small enough to escape the perceptive powers we’ve honed over millennia of human evolution. Our senses are fine-tuned to pick up the most minute acoustic variations—and for good reason, Bryant and [Athena] Aktipis write. Detecting feigned laughter is an important survival tool. “You have to be vigilant,” Bryant says, “because you want to discern whether people are trying to manipulate you against your best interests or whether they have authentic cooperative intentions.”