Like all adaptations, it helps us survive. It is the reaction to relief or to a stressful situation. Humans take care of other humans that they relate with and care about, and laughter brings us closer. As well as other humans looking out for us, they would be less likely to see these laughing humans as a threat and will not be as likely to kill them. The Laughing trait is passed on because the ‘laughers’ are more likely to survive until reproduction. Secondly, a laughing baby is more adorable and will be taken more care of. This, increases its odds of survival and reproduction. Additionally, laughter makes light of a situation, helping us in tense situations. It is also a quite threatening sound, when a bunch of humanoids are sitting around a fire, communicating, and letting out many loud chuckles. This would ward off predators, which increases odds of survival to reproduction. Lastly, people will pick a partner that they better relate to, and can make laugh. Thus, passing on the trait.