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Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
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mise à jour du
23 mars 2014
Proceedings of the Royal Society B
2014 B 281
Chimpanzees empathize with group mates and humans, but not with baboons or unfamiliar chimpanzees
 
Matthew Campbell, Frans de Waal

Chat-logomini

Human empathy can extend to strangers and even other species, but it is unknown whether non-humans are similarly broad in their empathic responses. We explored the breadth and flexibility of empathy in chimpanzees, a close relative of humans. We used contagious yawning to measure involuntary empathy and showed chimpanzees videos of familiar humans, unfamiliar humans and gelada baboons (an unfamiliar species). We tested whether each class of stimuli elicited contagion by comparing the effect of yawn and control videos. After including previous data on the response to ingroup and outgroup chimpanzees, we found that familiar and unfamiliar humans elicited contagion equal to that of ingroup chimpanzees. Gelada baboons did not elicit contagion, and the response to them was equal to that of outgroup chimpanzees. However, the chimpanzees watched the outgroup chimpanzee videos more than any other. The combination of high interest and low contagion may stem from hostility towards unfamiliar chimpanzees, which may interfere with an empathic response. Overall, chimpanzees showed flexibility in that they formed an empathic connection with a different species, including unknown members of that species. These results imply that human empathic flexibility is shared with related species.
-Campbell M et al. Computer animations stimulate contagious yawning in chimpanzees Proceed Royal Soc Biol 2009:276(1676):4255-4259
-Campbell MW, de Waal F. Ingroup-Outgroup Bias in Contagious Yawning by Chimpanzees Supports Link to Empathy. Plos One. 2011;6(4):1-4
-Campbell M, de Waal F. Methodological Problems in the Study of Contagious Yawning; In Walusinski O (ed): The Mystery of Yawning in Physiology and Disease. Front Neurol Neurosci. Basel, Karger, 2010, vol 28, pp 120&endash;127
-Campbell M, de Waal F. Chimpanzees empathize with group mates and humans, but not with baboons or unfamiliar chimpanzees. Proc. R. Soc. B 281: 20140013

Exploring the link between empathy and contagious yawning
Matthew W. Campbell & Frans B. M. de Waal

Empathy: Its ultimate and proximate bases F de Waal
L'âge de l'empathie De Wall F
Empathy and contagion of yawning: A behavioral continuity related to a behavioral discontinuity ?
B Deputte & O Walusinski
Tous les articles sur la contagion du bâillement
All articles about contagious yawning
 
1. Introduction
 
The concept of empathy is increasingly applied to explain animal sensitivity to the emotional states of others. Without necessarily implying the cognitively advanced forms found in human adults (e.g. theory of mind), it takes as its basis bodily connections and involuntary mimicry, also known as the perception&endash; action core of empathic processing [1].There are now studies of empathy in mammals, from mice (Mus musculus) [2], rats (Rattus norvegicus) [3] and dogs (Canis lupus familiaris) [4] to elephants (Loxodonta africana) [5], and also in birds [6,7].
 
One common behavioural measure is contagious yawning (CY), which appears to fit the empathy framework because of four key findings: (i) human adults high on other measures of empathy show more CY [8]; (ii) humans with developmental and personality disorders in which empathy is impaired show diminished CY [8&endash;11]; (iii) CY is positively biased by familiarity in humans (Homo sapiens) [12], chimpanzees (Pan troglodytes) [13], bonobos (Pan paniscus) [14], gelada baboons (Theropithecus gelada) [15] and dogs [16&endash;18], as is typical of other measures of empathy; and (iv) presented with a variety of body movements apes exclusively increase yawning in response to observed yawning, suggesting CY's high specificity [19,20].
 
Aiding this specificity, brain areas associated with the human mirror neuron system activate in humans viewing yawns [21&endash;23], withmirror neurons having been implied as a proximate neural mechanism for empathy [24,25]. Thus, CY fits better with an empathy framework than with explanations in terms of imitation or behavioural facilitation. Human empathic functioning, although biased towards similar and familiar individuals, is flexible enough to include empathy for strangers and even other species [26&endash;28]. Is an empathy response flexible enough to include strangers uniquely human, related to our well-developed capacity to cooperate with outsiders [29]? Empirical studies with non-humans show both the importance of familiarity in forming empathic connections and potential for moving beyond it. Mice showed heightened pain responses after viewing cage-mates in pain, but not after viewing strangers in pain [2]. Chimpanzees made a similar distinction, showing CY in response to familiar individuals but not unfamiliar individuals [13]. Rats, however, would help unfamiliar individuals, but only if the strain of rat was familiar [30]. Domestic dogs show empathy-related responses to unfamiliar humans [4,17,31] (although there are conflicting results with CY [32,33]), but with this species it is unclear whether this ability stems from natural or artificial selection. Young orphaned chimpanzees showed a CY response to an unfamiliar human [20], but positive interactions between the two may have influenced the response. A similar population of chimpanzees also showed helping behaviour towards an unfamiliar human [34].
 
When combined with anecdotes of inter-species helping behaviour [35], a pattern emerges that non-humans may indeed share some of the human's empathic flexibility. To explore the origins of flexible empathy in humans, we studied the responses of one of our closest living relatives, the chimpanzee, in which CY is well established [13,19,20,36&endash;38]. Chimpanzees live in fission&endash;fusion communities, which often compete [39,40]. Female migration at sexual maturity is the only movement of individuals between groups. In chimpanzee society, all known individuals are members of the community, and unknown individuals belong per definition to a different community. Using the contagiousness of yawning as a measure of involuntary body synchronization and empathy, we previously showed an ingroup&endash;outgroup bias: chimpanzees were affected by the yawns of known individuals, but not unknown individuals of their species [13].
 
However, having an existing positive relationship with an individual is not a prerequisite for contagion, as chimpanzees have also shown CY in response to computer-generated animations [37]. Is motor mirroring in chimpanzees flexible enough to induce yawns in response to species different from themselves? And would chimpanzees distinguish between known and unknown individuals from other species? Captive-reared chimpanzees interact daily with humans, so we wanted to know whether chimpanzees would express an empathic connection with humans in CY. However, chimpanzees may respond to known and unknown humans differently.
 
The research and animal care staff at the Yerkes National Primate Research Center Field Station use positive reinforcement when working with the chimpanzees. Hence, the chimpanzees have an established history of positive interactions with these specific individuals. Potentially, known humans may be categorized as something approaching an ingroup and unknown humans as something approaching an outgroup, with the latter potentially limiting the strength of a contagious response. To control for species familiarity,we also showed chimpanzees yawns from gelada baboons, a species they have never seen before. Videos of gelada baboons yawning were available from a previous study by Palagi et al. [15]. Comparing the response to humans and gelada baboons allowed us to test whether a familiar, meaningful species is necessary for crossspecies contagion, or whether cross-species contagion could be elicited via similarities in motor muscle activation alone. We employed the same experimental methods as in our previous study [13], which allowed us to compare the results directly as a gauge of how chimpanzees view familiar humans, unfamiliar humans and gelada baboons compared with their own species. This way, we could ask chimpanzees about how our species fits into their social world.
 
 
4. Discussion
 
The chimpanzees yawned significantly more when viewing the familiar human yawn video than the control. This result demonstrates that familiar humans did stimulate CY; however, we did not find that familiarity with the humans in the video was required. Unfamiliar humans stimulated the same yawn contagion, and the yawn rates were not significantly different from those for familiar humans. The third species tested, the gelada baboon, failed to elicit the same yawn contagion, however. Our interpretation is that chimpanzees do not need to know each yawning individual to show contagion, but the individuals do need to belong to a species with which the chimpanzees have a history of positive social interactions. We found a difference in the yawning rate between stimuli that did and those that did not elicit contagion (figure 2). Among the three stimuli that elicited contagion (i.e. ingroup chimpanzees, familiar humans and unfamiliar humans), the yawning rates were similar and none of these stimuli was more potent than another. Thus, we did not observe different magnitudes of CY, in contrast to human studies in which the degree of contagion follows a continuum based on social closeness [12]. Either humans are more discriminating in their CY responses, or we have not yet designed the experiment in the right way for chimpanzees.
 
Human stimuli elicited a similar level of contagion as the chimpanzees' friends and kin, and significantly higher than strange chimpanzees. For our subjects, a different species (but one they have a history of positive experiences with) was more potent at eliciting empathy-based contagion than outsiders of their own species. Many of our chimpanzees have not seen or interacted with strangers of their own species since the groups were assembled decades ago, while others were born into the group and may never even have seen a chimpanzee stranger. While it is possible that the arousal of seeing strange chimpanzees may have suppressed the physiological yawn response [45] irrespective of an empathic connection, increased yawning is also a possible outcome of high arousal [46], including in a CY context [47]. Rather, given the pervasive xenophobia among wild chimpanzees, in which strangers are invariably treated with hostility [40], we think that it is more likely that antagonism inhibited yawn contagion to the unfamiliar chimpanzee stimuli. Subjects may never have reached the positive engagement needed for an empathy-based response.
 
The human stimuli, on the other hand, are not expected to arouse the same hostility as our subjects are used to new people. Students come, complete their studies and leave, and care staff gain and lose members in the normal course of people changing jobs. The chimpanzees may have been conditioned to take a positive view of humans in general, not just the ones that they know. This is not to preclude that the chimpanzees do not make distinctions between familiar and unfamiliar humans, only that this distinction was not detected by our behavioural measure. How do the chimpanzees view gelada baboons? The rate of yawning was the same as that for outgroup chimpanzees (i.e. an absence of any significant contagion). Does this mean that chimpanzees responded with hostility to gelada baboons as well? This possibility cannot be excluded, yet given chimpanzee natural history it seems unlikely. At Gombe National Park, where chimpanzees interact freely with baboons (Papio anubis), affiliative interactions are common and competition between both species is limited [48].
 
Our data rather suggest a different possibility. The chimpanzees spent significantly more time looking at the outgroup chimpanzee videos than at gelada baboons or any other stimulus class (figure 3). Our subjects thus seemed far more interested in outgroup chimpanzees than gelada baboons, yet they showed a similar, minimal yawn response to both. Outgroup chimpanzees possibly elicited a hostile response, which interfered with empathybased engagement [49], whereas the gelada baboons were viewed as a socially meaningless stimulus. If true, we could say that CY with strange chimpanzees was actively thwarted, whereas with geladas it was not there to begin with. The different responses to the different stimuli further support the idea that CY is socially modulated, and thus serves as a measure of empathic engagement with the stimulus. As outgroup chimpanzees and gelada baboons did not stimulate significant rates of yawning, CY does not seem to be a simple fixed-action pattern for which any yawn may serve as a releaser. As for why humans but not gelada baboons stimulated contagion, physical resemblance or lack thereof probably does not alone account for the differences as outgroup chimpanzees did not stimulate CY. Rather, social experience probably plays a role.Would mere exposure to gelada baboons make them more familiar and lead to contagion? Or is mere exposure not enough and CY requires a history of positive social interactions, such as the chimpanzees have with most humans?
 
Most interestingly, could experience change the way chimpanzees respond to outgroup chimpanzees? These are unanswered questions. By forming measurable empathy-based contagion with unfamiliar humans, chimpanzees showed that the ability to connect with unfamiliar individuals is not unique to humans. Conditions within the human evolutionary lineage may have altered the expression of this ability, but flexible social engagementwas probably already present in the most recent common ancestor with chimpanzees. This flexibility opens a door to examining how we can modify who chimpanzees will form an empathy-based connection with and how strongly. Understanding this flexibility in social engagement may help explain the proximate mechanisms that allow for switching between cooperation and competition within chimpanzee and human societies [50].