A complete account of laughter must tell us something about its evolutionary origins. When did it first appear and from what antecedent behavior did it evolve? We begin by noting that laughter appears to be an instinctive behavior, observed in all human cultures, expressed within the first few months of life, and conveying the same sense of mutual vulnerability. Thus, laughter is at least as old as our species, roughly 200,000 years. To go further back in time, we must look to our closest surviving nonhuman relatives, the great apes: chimpanzees, gorillas, and orangutans. They have all been observed expressing laugh-like vocalizations, but is it “true” laughter akin to ours? In a word: yes. Their tickling, play chases, and rough-and-tumble play are comparable to that of young children, which means laughter was almost certainly employed by our common ancestor some 16 million years ago. What about the more distantly related lesser apes, the gibbons? They also play, but are much less social. There have been no signs of laughter in these species. From what behavior did it evolve? From the one that most resembles laughter. One that is also intimately related to, and expresses, something important about our feelings of vulnerability.