All animals yawn (see animalyawns.com) and in humans yawning seems to be contagious. Seeing another person yawn, or even just reading about yawning can make you yawn. (We talk about unconscious immitation in chapter 10 of the book). James Anderson from the University of Stirling gave a lecture in Sheffield last week about yawning – in the introduction he told us that when he lectures on yawning lots of people in the audience, well, yawn. But his talk was only yawn-inducing in the social-contaigon sense.
Yawning, it seems to me, may provide us with paradigm case of an automatic behaviour that, moving along the phylogenetic scale, has become co-opted into a quasi-voluntary social signal.
What am i trying to say and why does it matter? Well, speech – that most human of abilities – is another kind of action that may have begun as an automatic behaviour (mere vocal noises) before being subsequently tranformed into a social signal (alarm calls), and then again changed into being a mostly voluntary behaviour (like giving speeches to the UN, but not like my automatic, expletive, reaction when i fell down some stairs).
By looking at yawning we may get clues about how automatic animal behaviours change over evolutionary time into voluntary ones. By looking at yawning contaigon we might get clues about how our social nature affects our individual behaviours – and our individual control over those behaviours. In short, if this is the arena where human volition was born and is still mediated we need every ‘in’ we can get, and yawning may be one.
You can pretty precisely define what a yawn is. The characteristics are instantly recognisable: the screwed-up eyes, the head thrown back and of course – the gaping maw.
In humans a yawn typically lasts around six to eight seconds. At least twenty candidate functions have been suggested for yawning – and we still don’t know which ones could be true. It certainly isn’t just to do with the levels of oxygen in our lungs – some very thorough scientists have done experiments involving raising the ambient levels of carbon dioxide and found that it didn’t increase people’s frequency of yawning. We do know that it is found in all vetebrates and that it develops early – even 10 week old human foetuses yawn.
Like a lot of behaviours held in common by many species (it has even been suggested that fish yawn!), and which develop early in the lifespan, yawning seems to be controlled in the central, ancient, part of the brain – the brainstem. (And lets note here, that in monkeys vocalisations also seem to be brainstem controlled).
Studies have shown that in old-world monkeys yawning is more common amoung males, and amoung those monkeys higher up the dominance heirarchy. It could well be that in these creatures, like this baboon:
yawning has become a social signal of a different kind than in humans – a display of the canines and hence a warning to anyone thinking of causing trouble. The reports by some researchers that baboons are likely to yawn before fights, and possibly also likely to turn their heads in profile to the animal they are yawning at – better showing off those viscious teeth – would support this idea.
Another possible function for yawning amoung primates – including ourselves – is that it forfils a social coordination role. A way for a group to signal to itself something like “time for bed” or “we’re bored, let’s do something else now”. It’s not clear, however, why yawning would take on this role, nor, indeed, is it certain that a group of monkeys should all sleep at the same time.
Even in monkeys, yawning was making the transition into being a semi-voluntary behaviour. Dr Anderson reported evidence that yawning can be training into macque monkeys (using rewards for yawning behaviour). So, for primates at least, yawning is less than a reflex – perhaps a vital step on the path for a behaviour to become multi-purpose or a social signal. Although I wonder whether control-over-yawning was itself adaptive, or whether some more general increase in voluntary (cortical?) control allowed control-over-yawning as a by product.
Chimpanzees, closer relatives of ours than monkeys, shown videos by Dr Anderson of other chimps yawning, themselves yawned – showing that the yawning contaigon effect found in humans evolved before whatever happened that made us human.
In humans, Dr Anderson had done experiments showing that, unlike adult chimpanzees, pre-school children don’t catch yawning off others. This would fit with research in child psychology which suggests that, until around the age of three or four children, aren’t able to think about other people’s states of mind. They don’t have what many people would call empathy (and what psychologists call ‘Theory of Mind’). One aspect of this lack may be that they don’t socially mimic others like adults do, and hence don’t catch yawns.
You can bet that the next time i’m around a three year old I’ll be yawning at them to see if they copy me.
Supporting the connection between automatic contaigon of yawning is research published earlier this year by
Steven Platek, which showed that people who are higher in empathy are more likely to catch yawns off other people.
Dr Anderson made the prediction that primates without self-awareness (another aspect of theory of mind – if you can’t think about other people’s minds, how can you properly contextualise your own?) would, like human children but unlike adult chimps, not be subject to contaigous yawning.
But the purpose of yawning, and contaigous yawning in humans, is still an open question. During his talk Dr Anderson suggested that contaigous yawning “may just be a by-product of our capacity for low-level empathy”. So there is no one function to yawning – it became contaigous because it was a semi-automatic, partly-social signal and as our capacity to represent the thoughts of others developed yawning became infectious on the back of that capacity – a capacity which we can see the origins of in our nearest primate relatives. In this way yawning is like sleep, it isn’t fully understood and may in fact have many different functions. After arising in the common ancestor of all vetebrates it has had different roles put on it in different species – teeth display in baboons, and maybe some sort of social coordination function in chimpanzees. In humans yawning can reflect our profound capacity to unconsciously and automatically be influenced by the behaviour of others. Catching other’s yawns is fundamental to the social imitation that is so advanced in humans. And it doesn’t even have to be rude- some research, reported Dr Anderson, has suggested that yawning in synchrony is more common amoung potential lovers – not as a sign of bordom, but as an expression of their mutual empathy and attraction!