Humans are not the only animals that communicate. Birds sing to attract mates, dolphins use signature whistles that identify individuals, and many primates produce complex vocalisations that help them coordinate their social lives.
By studying these communication systems, researchers can reconstruct some of the evolutionary steps that eventually led to one of our defining traits: language.
Language doesn’t just mean making sounds – it requires an extraordinary ability to control them. Human speech demands precise coordination between breathing, the vocal folds across the larynx, and our tongue, lips and jaw.
Humans’ closest living relatives – chimpanzees and bonobos – possess vocal tracts that are more similar to ours than scientists once believed. Yet they do not seem to have the same fine voluntary control over the structures – starting with our lips and tongue – that allow us to produce rapid sequences of speech and such diverse sounds.
This raises an intriguing question: when did our ancient ancestors begin to acquire this remarkable vocal control? One possible clue comes from an unexpected source: laughter.
The evolution of laughter
For several years, I have studied the rhythmic structure of vocalisations in non-human primates. Rather than focusing on what calls mean, I have been interested in how they are produced.
The timing of vocalisations can reveal how breathing and vocal movements are coordinated, offering a window into the mechanisms that generate them. Whether analysing the songs of Madagascar’s indris lemur or the calls of orangutans, I kept coming back to the same question: how much control do different primates have over the rhythm of their voices?
Laughter turned out to be an ideal system for exploring this question.
Unlike speech, our ability to laugh is shared with all the great apes. Chimpanzees, bonobos, gorillas and orangutans all produce laughter-like vocalisations during play. Although these sound quite different from our familiar “ha ha ha”, they serve similar social functions, signalling playful intentions and strengthening social bonds.
Human laughter is much more diverse, however. We can produce loud belly laughs, quiet chuckles, giggles, snorts or almost silent laughter. We laugh when we are amused but also when we are embarrassed, nervous or trying to ease social tension. This flexibility makes laughter much more than a simple emotional reflex for us.
Human laughter is highly context-dependent. We laugh differently when we are genuinely amused, when we engage in polite social interactions, when we feel awkward, or when we share an inside joke.
Together with colleagues, I analysed 140 laughter bouts from humans and the four other great ape species. Instead of asking whether laughter sounded similar across species, we examined its rhythm: how quickly each laugh element followed the previous one, and how consistent that timing was. Our results revealed a clear evolutionary pattern.
When laughing, humans show greater temporal variability than our closest relatives. Chimpanzees and bonobos produce laughter at a slower rhythm than humans, while gorillas and orangutans laugh at an even slower pace.
In contrast, human laughter consists of more rapidly repeated elements – successive vocal bursts that together form a laugh. This increased flexibility may be one of the evolutionary changes associated with the emergence of finer voluntary control over vocal production.
In other words, humans’ ability to “laugh fast” may reflect one of the key innovations that eventually made speech possible.
The link between laughter and speech
The evolution of speech may not simply have involved producing new sounds, but changing the very tempo at which vocal actions are organised. Our findings suggest traces of this key evolutionary transition are still preserved in one of our most familiar activities: laughing.
While humans and chimpanzees share a common evolutionary history, we will never hear how our ancient ancestors laughed. Fossils preserve bones not vocalisations, so the only way to reconstruct the evolution of laughter is by comparing living species and inferring the changes that occurred along the hominin lineage.
Because we found that chimpanzee and bonobo laughter differs from human laughter in rhythmic structure and temporal variability, we can use these living species to infer that early hominins may have exhibited laughter patterns which were already distinct from those of other great apes during the evolutionary transition towards modern human laughter.
Three-to-four million years ago, early hominins may already have shown some of the foundations of the flexible laughter patterns seen in humans today. Our findings suggest that increased temporal variability in laughter evolved along the hominin lineage. This may have enabled laughter to become increasingly adapted to different social contexts, from playful interactions to maintaining social bonds and signalling affiliation.
Every time we compare ourselves with our closest great ape relatives, we discover that the gap between humans and other apes is smaller than was once imagined. Yet we also uncover subtle differences that may have had profound evolutionary consequences.
Laughter is one of them. It may seem like a simple expression of joy, but hidden within its rhythm is a record of millions of years of evolution – and, perhaps, one of the clues to how our human ancestors eventually found their voice.
You must be logged in to post a comment Login