 When you ask, why do we laugh? We can answer that in terms of what are the situations in which we laugh, but we can also answer it in terms of the broader evolutionary pressures that might have led to us laughing. And in order to address those kinds of questions, it's really useful to look at other species. And there are researchers who've made it their delightful work to go around and tickle primate babies. And what they have found is that