Children can be cheeky monkeys, they also laugh like chimpanzees! Babies and baby chimps chuckle while inhaling and exhaling, unlike adult humans who laugh mainly during exhalation.
It’s thought that babies, like apes, don’t have full control over their vocal muscles, so they laugh as they inhale as well as when they exhale. But as humans age, laughter becomes less chimp-like and more human-like.
Both humans and chimpanzees are great apes, or Hominids, and include orangutans, gorillas, chimpanzees and bonobos. Chimps are our closest cousins – but laughter is a behaviour that differs between species. When an adult human laughs, they initially inhale before producing ‘ha ha ha’ sounds in short bursts, starting loud and then fading away.
As babies get older they start to laugh more like grown-ups. It may be that babies learn to imitate their parent’s laughter in the same way that babies learn to interpret the facial expressions, smiles and the tone of voice of their parents.
Researchers collected recordings of babies’ laughter aged between 3 and 18 months old. These were played to 196 volunteers and 15 expert phoneticians, who had to judge the extent to which the laughter was produced during inhalation or exhalation, and the extent to which they found the laughter pleasant and contagious.
The result of this experiment was that laughs produced while exhaling were rated as more pleasant and contagious than those produced while inhaling. But it was the older infants in the sample — the ones nearer the 18-month mark — who exhaled more as they laughed, suggesting that during this key period of development — between 3 and 18 months old — infants learned to exhale when they laugh.
Laughter produced by exhaling tends to be louder, which makes it easier for babies to communicate that they are having fun and want to continue playing. As babies get older, they learn the ‘communicative function’ of laughter and that this communication is better achieved by exhaling rather than inhaling. In short, babies may be subconsciously adapting their laughter to get the best reaction from their parents.
In another experiment, 102 people were asked to rate recordings of laughing babies and adults without focusing on their breathing and this time, the researchers found they preferred more singsong adult-style laughs even when they were not thinking about the style of the laugh.
Could it be that our behavioural and vocal repertoire is ancient — even inherited from the common ancestor we share with apes.
The study, entitled ’The ontogeny of human laughter’, was published in the journal Biology Letters.
In addition to laughter, like humans, chimpanzees can remember each other even after years of being separated.
Researchers headed by Dr Laura Lewis, from the University of California, Berkeley and Christopher Krupenye, from Johns Hopkins University, used eye-tracking cameras to record where the primates gazed when they were shown side-by-side images of other chimps or bonobos. One picture was of a stranger, while the other was of a chimp or bonobo they had lived with for a year or more at some point in their life — the chimp’s eyes lingered significantly longer on images of those they had previously lived with, suggesting a degree of recognition. They also looked longer at apes with whom they’d had more positive relationships.
In one case, a bonobo named Louise had not seen her sister or nephew for more than 26 years. When the researchers showed her their images, her eyes honed in on both of them.
The study proves how similar we are to these primates… and how similar they are to us.
Previous research shows dolphins recognise one another’s signature calls for up to 20 years. The findings also bolster the theory that long-term memory in humans, chimpanzees and bonobos likely comes from a shared common ancestor that lived between 6 and 9 million years ago.
These are not the only similarities between apes and humans. Like humans, monkeys also give in to peer pressure. A nine-year study of 250 Vervet monkeys in South Africa found that social traditions are transmitted through different communities of monkeys.
Scientists from the University of Lausanne in Switzerland and Paul Sabatier University in France found that male monkeys who join sociable communities quickly adapt their behaviour to match the social mores of their new group. Three different communities of monkeys showed big differences in how sociable the monkeys were in each.
Members of one group exchanged grooming more reciprocally, meaning that when a monkey was groomed it would usually return the favour. Overall, the monkey’s behaviour adapted to that of each of the new groups they joined.
Primates, including vervet monkeys, have highly advanced social systems and can maintain long and complex relationships with other members of their species, using common social behaviours to establish and maintain new social bonds, as well as mimicking social behaviours and social fashions of the new group.
These changes in behaviour could be due to an unconscious mimicry or ‘peer pressure’ from other monkeys. Either way, social influences were definitely influenced by other members of the group almost certainly to help them become part of their new community and better integrate into a new group.
Perhaps unsurprisingly, it was the females who were largely responsible for setting social styles within a group and this influence was stronger when the groups had a higher ratio of females to males, suggesting that females act as ‘models’ for social learning and form the social core of the group. So just like humans then…