You may be surprised to learn that laughing babies are a central part of human evolution. To understand this, we need to know why we evolved our giant brains and what is the purpose of laughter. The answer in both cases is human connection. Laughter is not primarily about jokes and surprises. It is, in the words of Danish comedian Victor Borge, 'the shortest distance between two people'. It’s a way of strengthening social bonds, especially between babies and their families. Playing peekaboo illustrates this perfectly. It is the most reliable way to make a baby laugh and they laugh because you are giving them your undivided attention (the game doesn’t work if you don’t).
The same is true for adult laughter. American laughter research pioneer Robert Provine eavesdropped on lots of conversations in college cafeterias. He observed that most laughs were not connected to jokes or funny statements but markers of social inclusion. British evolutionary psychologist Robin Dunbar replicated this work eavesdropping in pubs and noticed something else. Laughter works well in groups. This led him to a novel theory that we got to be so brainy because we are so social.
Laughter and evolution
In the last two million years, the brains of our ancestors tripled in size, from around 500 to 1500 cubic centimetres. At the same time, social groups probably also tripled from the 40–50 typical of other primate troops to around 150 typical of modern hunter-gatherer tribes: a group size famously known as 'Dunbar’s number'. Dunbar thought these two increases were closely related. Large group size would be beneficial to puny primates trying to survive on the African savannah; it would let them share resources and band together for protection. And large brains would be required to keep track of on the complex web of social relations.
As group sizes got larger, new skills were required to maintain group cohesion. Chimpanzees spend hours grooming each other. The time and effort involved make it an ‘honest signal’ of friendship and affiliation, but it becomes impossible in larger groups. Dunbar proposed that the one-to-many sharing of laughter and emotional signals were a form of vocal grooming. He believes this proto-gossip evolved into language, further driving our success and our developing intelligence.
But big brains create big dangers in childbirth and challenges in child-rearing. Babies are born extremely helpless and need a huge investment from clever caregivers. Psychologists Steve Piantadosi and Celeste Kidd realised this investment could create a positive feedback loop leading to even bigger brains.
Last of all, let’s not forget the babies themselves. They must learn language and all other social skills to fit into the community, culture and ecosystem. They must bootstrap this for themselves because evolution did not build in lots of hard-wired instincts. Instead, babies are driven by gleeful curiosity. They are the champions of humanity’s remarkably adaptable general intelligence and playful sociability. The cradle of humanity echoed to the sound of thousands of generations of laughing babies. Be sure to thank the next baby you meet.