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- mise à jour
du
- 18 août
2025
- Sci Rep.
- 2025;15(1):18002
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- Chimpanzees
yawn when observing an android
yawn
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- Joly-Mascheroni R, Forster B, Llorente
M,
- Valsera C, Gomara A, Crailsheim D,
Calvo-Merino B
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- -Joly-Mascheroni
RM, Senju A, Sheperd AJ Dogs catch human
yawns Biology
letters Animal Behaviour.
2008;4(5):446-448
- -Joly-Mascheroni
R, Forster B, Llorente M, Valsera C, Gomara A,
Crailsheim D, Calvo-Merino B. Chimpanzees
yawn when observing an android yawn. Sci Rep.
2025;15(1):18002.
-
- Abstract
- This study explores contagious yawning in
adult chimpanzees (Pan troglodytes) in the
presence of a non-biological humanoid agent, an
android. Chimpanzees observed an android
portraying specific facial expressions,
including yawns and gapes. The results showed
that adult chimpanzees exhibited across-agent
yawn contagion, with a graded response: the
highest contagion occurred when the android
displayed a fully wide-open mouth (Yawn
condition), a reduced response when the mouth
was partially opened (Gape condition), and no
contagion when the android's mouth was closed
(Close condition). Additionally, chimpanzees
engaged in behaviours associated with
drowsiness, such as gathering bedding materials,
constructing nests, and lying down, while
observing the android yawning. This suggests
that yawning by an unfamiliar model may act as a
contextual cue for rest, rather than merely
triggering a motor resonance response. These
findings contribute to the understanding of
non-human primates' susceptibility to
contagiously induced behaviours, specifically
yawns, even when triggered by an artificial
agent. This study highlights the role of social
factors in shaping yawn contagion and calls for
further research on cross-species and
cross-agent interactions.
-
- Résumé
- Cette étude explore les
bâillements contagieux chez les
chimpanzés adultes (Pan troglodytes) en
présence d'un agent humanoïde non
biologique, un androïde. Les
chimpanzés ont observé un
androïde présentant des expressions
faciales spécifiques, notamment des
bâillements et des gags. Les
résultats ont montré que les
chimpanzés adultes présentaient
une contagion des bâillements d'un agent
à l'autre, avec une réponse
graduée : la contagion la plus forte se
produisait lorsque l'androïde affichait une
bouche complètement ouverte (condition de
bâillement), une réponse
réduite lorsque la bouche était
partiellement ouverte (condition
d'écartement), et aucune contagion
lorsque la bouche de l'androïde
était fermée (condition de
fermeture). En outre, les chimpanzés ont
adopté des comportements associés
à la somnolence, comme rassembler des
matériaux de couchage, construire des
nids et s'allonger, tout en observant
l'androïde en train de bâiller. Cela
suggère que le bâillement d'un
modèle non familier peut agir comme un
indice contextuel de repos, plutôt que de
simplement déclencher une réponse
de résonance motrice. Ces
résultats contribuent à la
compréhension de la susceptibilité
des primates non humains aux comportements
induits par la contagion, en particulier les
bâillements, même lorsqu'ils sont
déclenchés par un agent
artificiel. Cette étude met en
évidence le rôle des facteurs
sociaux dans la contagion des bâillements
et appelle à des recherches plus
approfondies sur les interactions entre
espèces et entre agents.
Introduction
- Processes essential for social interaction
between humans may also play a role in
interactions with non-human agents, such as
robots or androids. Human-robot interactions tap
into mechanisms related to empathy?,
perspective-taking2,3, and sensorimotor
simulation 4,5,6, which are further modulated by
the observer's familiarity with the agent or
action 2,8,9,10.
- Animal research based on observations of
non-verbal behaviour analysis has provided
insights into the evolutionary origins and
mechanisms underlying social interaction. While
most of this research has focussed on
interactions between conspecifics, via screen
presentations 12,13 , cross-species research has
broadened our understanding of these processes,
including contagious yawning'. Here, we expand
social animal research by examining interactions
beyond biological species to reach across to
agents, specifically by investigating the
behavioural response of our closest evolutionary
relatives (chimpanzees) to a non-conspecific,
non-biological agent performing various
actions.
- Understanding interactions beyond biological
agents in a real-word setting can enhance our
comprehension of core social mechanisms, by
directly examining the contingency of social
attributes such as empathy and contagion.
Specifically, in this study, we explored
contagious yawning in chimpanzees when observing
a humanoid android presenting a yawning
movement, a control action (gaping), or
remaining motionless with its mouth closed.
-
- On contagious yawning, empathy, and
imitation
- The embodied nature of yawning has been
widely used to examine contagious intransitive
actions in primates, including humans15
bonobos!® and chimpanzees, as well as
nonprimate species, such as dogs'& sheep 9
elephants20 and budgerigars21. While several
influential theories about the potential
multifunctional features of yawning have been
postulated in various species22,23,24, the
ultimate function of spontaneous yawns remains
debated25. Yawning has been associated with
physiological26 and social events27,
thermoregulatory28, , including transitions
between rest and arousa 29 , attention
modulation 30 and group synchronization?1.
Furthermore, the contagious aspect of yawning
has been intertwined with core elements of
social interaction, such as empathy?, (but see
33,34) emotion processing35, and
imitation36.
- The developmental trajectory of contagious
yawning (CY) supports its association with
empathy-related processes. CY emerges gradually
in humans, chimpanzees, and dogs, becoming
prominent at around 4 years in humans, 5 years
in chimpanzees, and 7 months in dogs 37,38,39.
This aligns with the maturation of other
cognitive and social abilities, such as
perspective-taking, attention to and
identification of others' mental states
(children40; chimpanzees41; dogs42), and what is
sometimes referred to as affective
empathy43.
-
- Yawn contagion has also been interpreted as
a particular type of emotion contagion* (but
see45). Proponents of this perspective suggest
that CY relies on two interconnected processes:
non-conscious mimicry and afferent feedback**.
Non-conscious mimicry, also known as the
"chameleon effect"47,48, refers to the tendency
to mirror others' behaviours involuntarily in
social interactions, for example, copying
postures, facial expressions, or movements
without conscious awareness or intent. Afferent
feedback occurs when gestural communication and
facial expressions influence emotional
experiences, as seen in reciprocal smiling*9, or
even in whole-body postural effects50,51.
Mimicry or imitation® play a fundamental
role in reinforcing social bonds through an
emotional feedback loop»3. In humans, being
mimicked increases affinity, liking, and
empathic responses®4, including compassion"S
, and promotes prosocial behaviour not only
towards the mimicker but also towards unrelated
individuals in the same social context 6,52
- Social motivations, such as the desire to
establish bonds, can increase non-conscious
mimicry in humans58,59. Similarly, in many
animal species, offspring copy their parents,
for example, in hunting or self-maintenance
behaviours60. These phylogenetically conserved
mechanisms support social learning®.
Moreover, imitation-based social interactions
have been reported across various species. For
instance, capuchin monkeys (Sapajus apella)
exhibit greater affiliative behaviour towards
humans who imitate them®2. Consistent with
the idea that humans preferentially mimic
socially significant individuals®3, yawn
contagion is more likely to occur between
socially bonded individuals in several species,
including chimpanzees64, bonobos65, gelada
monkeys66, and possibly dogs67,68.
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- Robots and human-like agents in social
interaction
- The advancements in artificial intelligence
and computer science have enabled the creation
of robots (hereafter: "android") and agents with
human-like features (e.g., realistic gestures
and speech) to study social interaction69,70.
Typically, the term "robot" refers to a
physically embodied system, whereas "agent"
denotes a software-based system?1,72.
Neuroimaging studies have investigated how
humans process actions performed by androids3,
revealing that the same observation network is
engaged when observing either a human or an
android performing an action 4,15,26, though
this remains a topic of debate. At a behavioural
level, humans tend to apply their common social
norms when interacting with androids, adjusting
their responses based on the android's
human-like facial features". For example,
androids with infant-like facial features are
perceived as more sociable and friendly?8 , and
participants tend to cooperate with a software
agent that has a human face to the same extent
as they would with another person??. Similarly,
when an android mimics human behaviour 2 or
demonstrates perspective-taking abilities80 -,
people develop more positive attitudes towards
it. Generally, humans tend to attribute
human-like qualities to non-biological agents
that possess anthropomorphic
characteristics®1,82.
-
- To understand the evolutionary roots of
flexible "cross-agent" social interaction
mechanisms, we evaluated behavioural responses
of chimpanzees to facial movements performed by
an unfamiliar, non-biological agent, namely a
human-like android. To this end, we developed an
android head capable of executing facial motor
actions with precise motor and temporal accuracy
(see Fig. 1a). Specifically, we tested whether
adult chimpanzees would exhibit yawning when
observing an android simulating yawns. We
predicted that chimpanzees would yawn more
frequently in the Yawn condition compared to the
Gape (opening of the mouth but not as wide as in
a yawn with neutral, non-emotional expression
and no particular significance (control
movement)) and Close (mouth closed, no movement)
conditions (see Fig. 1a). Additionally, we
recorded baseline measurements of chimpanzee
behaviour on a typical day to compare against
experimental conditions. To further explore the
chimpanzees' responses to the android, we
analysed additional behaviours, including the
duration of lying down (a resting position
indicative of low arousal) during and after the
android's movements across the three
experimental conditions.
-
- Discussion
- To our knowledge, this is the first study to
explore contagious yawning in response to an
inanimate agent, an android, presented in real
time. More than half of the adult chimpanzees
exhibited yawn contagion across agents.
Specifically, their yawning frequency increased
significantly in response to the android's
yawning condition compared to the Gape, Close
and Baseline conditions. Interestingly, no
yawning was observed in the Gape or Close
conditions, and only one chimpanzee yawned
during the Baseline phase, suggesting that
spontaneous yawning was rare under these
circumstances. In addition, chimpanzees spent
more time lying down in the Yawn condition than
in the Close condition, potentially indicating a
soporific effect of observing yawning, as some
individuals also gathered bedding materials
before lying down.
-
- Our findings align with previous research of
intra-species contagious yawning such as in
humans84, chimpanzees85 bonobos86,8z
orangutans®& and inter-species effect,
such as yawning transmission from humans to
chimpanzees38 adult dogs14,60 or puppies31,
However, in the present study the stimulus was
an unfamiliar non-biological agent with
human-like features. The chimpanzees' response
suggest that yawning does not necessarily
require social familiarity or a conspecific
model, but can be triggered by an unfamiliar
agent exhibiting biologically relevant
cues.
-
- The mechanisms underlying this response
remain unclear®9. One possibility is that
chimpanzees deliberately engaged with the
unfamiliar android, intending to interact,
imitate, or bond with it90,91. Alternatively,
the observed yawning may have triggered an
automatic perception-action coupling mechanism,
leading to an embodied response without explicit
intent®2. This interpretation is consistent
with theories suggesting that yawning contagion
results from basic motor resonance rather than
complex social cognition.
- Interestingly, the increased yawning
frequency in the Yawn condition coincided with
greater lying down behaviour, despite the
android never performing actions other than
yawning, gaping, or closing its mouth. This
pattern suggests that yawning may have signalled
restrelated associations for the chimpanzees.
The chimpanzees' behaviour possibly resulted
from inferences or associations evoked by the
observed yawn, or their own yawn, contagiously
induced or not. The chimpanzees' immediate
response to seeing the android's yawning could
reflect an uncontrollable urge to react or
re-enact. Here, re-enacting would consist of
immediately yawning as well, while reacting
would possibly involve perceiving the yawn as
carrying further information, i.e. the android's
yawns being perceived as a signal that it was
the place and time to lie down and rest.
Furthermore, the chimpanzees did not display
this behaviour in the Gape or Close conditions,
giving further support to the inferential
processes resulting from only the yawn stimuli.
Overall, this is the first study to demonstrate
that one of our genetically closest primates
displays reproduction of an observed action, and
adds associated behaviours such as lying down,
even when the observed action is performed by a
non-biological agent.
-
- These findings warrant further studies of
interactions between androids, humans and other
species in general, and in particular, action
perception, understanding and interpretation.
For example, are other movements or actions
performed by robotic agents contagious to humans
or non-human animals? Conceivably, in
humans®1 the phylogenetically old phenomenon
of spontaneous yawning, particularly its
contagious aspect, may have been part of a
prelanguage form of communication. Contagiously
induced or not, in other animals it may have had
a functional role in social interactions
involving comparable information-processing
mechanisms, and maintained through evolution
®1,82.
- Regardless of the potential interpretations,
our findings indicate that chimpanzees exhibit
yawn contagion, triggered by a non-biological
inanimate agent, a humanoid android, that looks
as if it is yawning. Yawning, despite its
elusive primary functions, may still have an
evolutionarily old, non-verbal communicative
role, and its contagious aspect may help us find
out more about how humans and animals developed
adaptive functions, ways of communication,
synchronisation and social interaction 83,84,94
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