While juvenile chimpanzees (5-8 years of age) catch human yawns, infant chimpanzees seem immune to yawn contagion. Aside from humans, cross-species yawn contagion has previously only been demonstrated in dogs.
Yawning together is not just a sign of being tired at the same time. Previous research, on adult humans, chimpanzees, bonobos, baboons and dogs, has suggested that contagious yawning may be used as a measure of empathy, that is, the ability to feel or imagine others’ emotional experiences. One argument for this is that we tend to be more susceptible to catching yawns from those we are close to.
The Lund University research was carried out at Tacugama Chimpanzee Sanctuary in Sierra Leone, where 33 orphaned chimpanzees, aged between 13 months and 8 years, engaged in bouts of playful interaction with a researcher, who repeatedly yawned, gaped (simply opening of mouth without yawning) or wiped her hand over her nose. Yawning, but not nose-wiping, was contagious. While younger chimpanzees did not respond to yawning, chimpanzees above 5 years of age yawned contagiously – that is, they yawned more in the yawning context than in any of the other ones.
As a way of examining the role that empathy with the yawner played for contagion, the study also compared the chimpanzees’ reactions towards yawns from their human surrogate mother and a stranger. Contrary to prediction, there was no difference in the likelihood of yawning when engaging with an unfamiliar person from someone with whom the chimpanzees had a close relationship.
The developmental pattern found in the study is consistent with what previous research has found for humans. Humans also show a developmental increase in susceptibility to yawn contagion, with children seemingly beginning to yawn contagiously around the age of four. This is the time when empathy-related behaviours and the ability to accurately identify others’ emotions begin to manifest clearly.
One interpretation that the researchers propose is that the results of the study reflect a general developmental pattern, shared by humans and other animals. Given that contagious yawning may be an empathetic response, the results can also be taken to mean that empathy develops slowly over the first years of a chimpanzee’s life.
But what does the lack of differentiation between the surrogate mother and the unfamiliar human mean?
“We do not have the full explanation yet, as it is a complex phenomenon that is being explored”, Elainie Madsen, who was part of the Lund University research team, says.
There are at least two possible explanations. One is that familiarity – which has been used to stand for empathy – seems to play out differently in immature and adult individuals. The present study suggests that juvenile chimpanzees generalise their yawn responses to humans, irrespective of familiarity and attachment history. In contrast, previous research on adult chimpanzees has shown that contagious yawning is targeted mostly towards familiar individuals. This research on adult individuals has, however, been conducted on chimpanzees that have seen other chimpanzees yawn, and furthermore only on video. The researchers are therefore cautious.
“Future research will have to examine whether there might be multiple reasons for yawning in response to others’ yawns, and whether these differences apply differently within and between these two species. That is, whether chimpanzees may apply ‘targeted empathy’ to interactions with members of their own species – and selectively catch yawns from familiar chimpanzees – while they apply a more generalised form of empathy to interactions with humans. A reason for this may be that chimpanzees typically engage in competitive, even hostile, relationships with unfamiliar members of their own species, but rarely do so with humans, who they mostly experience as cooperative. Alternatively, it is possible that younger chimpanzees switch from a ‘generalised empathy’ to all individuals – irrespective of species – to a more ‘targeted empathy’ as they mature into adults and possibly have stronger reasons to differentiate friends from foes”, Madsen concludes.
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Madsen, E.A., Persson, T., Sayehli, S., Lenninger, S., Sonesson, G. (2013) Chimpanzees show a developmental increase in susceptibility to contagious yawning: A test of the effect of ontogeny and emotional closeness on yawn contagion. PLoS One
Elainie Madsen, PhD, Evolutionary Psychologist
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