Something like laughter

The first hoots of laughter from an ancient ancestor of humans rippled across the land at least 10 million years ago, according to a study of giggling primates.

Researchers used recordings of apes and babies being tickled to trace the origins of laughter back to the last common ancestor that humans shared with modern great apes, which include chimpanzees, gorillas and orangutans.

The finding challenges the view that laughter is a uniquely human trait, suggesting instead that it emerged long before humans split from the evolutionary path that led to our primate cousins, between 10m and 16m years ago.

“In humans, laughing is a complex and intriguing expression. It can be the strongest way of expressing how much we are enjoying ourselves, but it can also be used in other contexts, like mocking,” said Marina Davila Ross, a psychologist at Portsmouth University.
“I was interested in whether laughing had a pre-human basis, whether it emerged earlier on than we did.”

Davila Ross travelled to seven zoos around Europe and visited a wildlife reserve in Sabah, Borneo, to record baby and juvenile apes while their caretakers tickled them. Great apes are known to make noises that are similar to laughter when they are excited and while they are playing with each other.

“The caretakers play with the apes all the time and tickling is a very important part of that. There are certain body parts that are more ticklish than others, depending on the individual. Some were tickled on their necks or armpits, while others offered their feet to be tickled,” said Davila Ross.

In total, Ross collected recordings of mirth from 21 chimps, gorillas, orangutans and bonobos and added recordings of three babies that were tickled to make them laugh.

To analyse the recordings, the team fed them into a computer program that arranged them on an “evolutionary tree” based on how related to each other they seemed to be.

Remarkably, the laughter recorded from different primates linked together in a way that matched the evolutionary tree linking all of the species to one common ancestor.

“Our evolutionary tree based on these acoustic recordings alone showed that humans were closest to chimps and bonobos, but furthest from orangutans, with gorillas somewhere intermediate. And that is what you see in the well-established evolutionary tree of great apes,” said Davila Ross. “What this shows is strong evidence to suggest that laughing comes from a common primate ancestor.”

Writing in Current Biology, researchers describe how the earliest laughter-like sounds were shorter and noisier, but with time became longer and clearer as the great apes evolved.

Human laughter sounds very different from the noises produced by great apes.

The differences are thought to have arisen when certain acoustic features became exaggerated in early humans after they split from ancestors they shared with chimps and bonobos around 5.5m years ago. Humans laugh as they exhale, but chimps can laugh as they breathe in as well. The human laugh is also produced by more regular vibrations of the vocal cords than in any of the apes.

Few studies have been carried out into the role of laughter in primates, but at least one study has suggested that it is important in expressing excitement and arousal. Laughing might also have been important for bonding within groups of animals.

Robert Provine, a psychologist and neuroscientist at the University of Maryland and author of the book Laughter: A Scientific Investigation, said students who took part in his own studies likened chimp “laughter” to a dog panting, an asthma attack or hyperventilation. Some even thought the noise was caused by someone sawing.

“The means of production of human and ape laughter are as different as the sound, with the ape vocalisation being produced during both inward and outward breaths, while the human parse an outward breath into 'ha-ha'," he said. “The simplicity and stereotypy of laughter provides a valuble tool with which to trace vocal evolution, much as simpler systems of molecular biology are useful for investigating complex life processes,” he added.