https://aeon.co/ideas/five-month-old-babies-know-whats-funny

Perhaps because infants are so young, we have been reluctant to credit them with understanding ‘funniness’. Their laughs are more often attributed to ‘gas’ (a myth long ago dispelled) or imitation, or having been reinforced for laughing in response to certain events – like Mom singing in an ‘opera voice’. As it turns out, getting the joke doesn’t require advanced cognitive skills. And much of what it does require is within the infant’s grasp.

Although infants do imitate smiling, starting in the first few months of life, and prefer to look at smiles compared with negative emotional expressions, and although they might be reinforced for laughing at particular events, these are not sufficient explanations for infant laughter and humour. If they were, then imitation and reinforcement would need to account for most infant laughter, and this is simply not the case in life or in the research lab. In addition, it would suggest that infants are not capable of understanding new humorous events unless someone were available to interpret for them and/or to reinforce their laughter. Instead, research has shown that, within the first six months of life, infants can interpret a new event as funny all by themselves.

So how do they do it? Like children and adults, infants appear to rely on two key features to detect funniness. First, humour nearly always requires a social component. Using naturalistic observations, the psychologists Robert Kraut and Robert Johnston at Cornell, and later the neuroscientist Robert Provine at the University of Maryland, discovered that smiling is more strongly associated with the presence of other people, and only erratically associated with feelings of happiness. That is, smiling is more likely to be socially rather than emotionally motivated. Thus, the presence of a social partner is one key component of finding something funny. Recall that the point of laughter is to be shared.

But humour has a cognitive element too: that of incongruity. Humorous events are absurd iterations of ordinary experiences that violate our expectations. When a banana is used as a phone, when a large burly man speaks in a Mini Mouse voice, when 20 clowns emerge from a tiny car, we are presented with something bizarre and irrational, and are left to make sense of it. Infants, too, engage in this process.

We showed six-month-olds ordinary events (a researcher pretending to drink from a red plastic cup) and absurd iterations of those events (the researcher pretending to wear the red cup as a hat). In one condition, we instructed parents to remain emotionally neutral during the absurd event. Not only did infants find the absurd version of the event funny, they found it funny even when their parents remained neutral. That is, infants did not rely on their parents’ interpretation of the event as ‘funny’ to find it humorous themselves. When repeated with five-month-olds, we got the same results. Even with only a month of laughter experience under their belts, five-monthers independently interpreted the funniness of an event.