Psychology and Evolutionary
Behavioral Sciences Programs,
SUNY Polytechnic Institute,
Utica, NY 13502, USA*
Abstract
Contagious yawning, or the reflexive
tendency to yawn following the detection of
yawning in others, is well-documented among
humans and a growing number of social
vertebrates. While the most common form of yawn
contagion occurs between conspecifics, some
non-human animals in captivity have been
reported to yawn in response to yawns from human
handlers/caregivers. The current research sought
to provide the first formal investigation of
whether people yawn contagiously in response to
yawns from non-human animals. In addition, this
study aimed to test whether this response was
modulated by phylogenetic relatedness and
domestication/social closeness. A total of 296
participants from Amazon Mechanical Turk
self-reported on their yawning behavior
following exposure to a (1) control
(non-yawning) condition or a compilation of
yawning stimuli either from (2) fish, (3)
amphibians, (4) reptiles, (5) birds, (6)
non-primate mammals, (7) apes, or (8)
domesticated cats and dogs. The results provide
strong support for interspecific yawn contagion.
However, neither the propensity to yawn (binary)
nor total yawn frequency varied significantly
across interspecific conditions. Overall, these
findings suggest that the mechanisms governing
yawn contagion can be activated by varied forms
of yawning stimuli, including those from
distantly related and unfamiliar species
Résumé
Le bâillement contagieux, ou la
tendance réflexe à bâiller
après avoir détecté le
bâillement d'autrui, est bien
documenté chez les humains et un nombre
croissant de vertébrés sociaux.
Bien que la forme la plus courante de contagion
du bâillement se produise entre
congénères, certains animaux non
humains en captivité ont
été signalés comme
bâillant en réponse aux
bâillements des personnes qui les
manipulent ou les soignent. La présente
recherche visait à fournir la
première enquête formelle sur la
question de savoir si les gens bâillent de
manière contagieuse en réponse aux
bâillements d'animaux non humains. En
outre, cette étude visait à
vérifier si cette réponse
était modulée par la
parenté phylogénétique et
la domestication/proximité sociale. Au
total, 296 participants d'Amazon Mechanical Turk
ont fait part de leur comportement de
bâillement après avoir
été exposés à une
condition (1) de contrôle (sans
bâillement) ou à une compilation de
stimuli de bâillement provenant (2) de
poissons, (3) d'amphibiens, (4) de reptiles, (5)
d'oiseaux, (6) de mammifères non
primates, (7) de singes ou (8) de chats et de
chiens domestiqués. Les résultats
confirment la contagion interspécifique
du bâillement. Cependant, ni la propension
à bâiller (binaire) ni la
fréquence totale des bâillements ne
varient de manière significative entre
les conditions interspécifiques. Dans
l'ensemble, ces résultats
suggèrent que les mécanismes
régissant la contagion du
bâillement peuvent être
activés par diverses formes de stimuli de
bâillement, y compris ceux provenant
d'espèces lointaines ou inconnues.
Tous
les articles d'Andrew Gallup
Yawning is a complex reflex that has been
documented across all classes of vertebrates
[1,2,3,4]. From an evolutionary
perspective, this stereotyped motor action
patten appears to be a neurological adaptation
that stimulates changes in state [5] and
arousal [6] through intracranial
circulation and brain cooling
[7,8,9,10]. While yawning occurs with
greatest frequency around sleeping and waking
transitions [11,12,13,14], this response
is also considered a displacement behavior that
can be indicative of stress or conflict
[15,16]. Built atop these primitive
functions, yawning has taken on derived social
features [17,18]. In particular, the
reflexive tendency to yawn following the
detection of yawns in others, i.e., contagious
yawning, is a well-documented phenomenon that
may serve to enhance vigilance and
synchronization in groups [19]. Distinct
from physiologically triggered yawns, which are
ubiquitous in vertebrates, there is a great deal
of variation across species when it comes to the
tendency to yawn contagiously
[20,21,22,23].
Psychological experiments on humans have
consistently found that people yawn in response
to seeing, hearing, and even thinking about
other people yawning [5,24,25], while
individual differences in this response are
related to variability in biobehavioral
synchrony [26,27]. Yawn contagion is
also common among non-human great apes,
including chimpanzees [28,29], bonobos
[30,31], and orangutans [32].
However, studies on gorillas consistently show
no evidence for this effect [33,34]. One
experiment also indicated contagious yawning
among a subline of high-frequency-yawning rats
[35]. Observational studies of the
naturalistic frequency of yawning also suggest
contagion among gelada baboons [36,37],
wolves [38], domesticated pigs
[39], and African lions [17]. In
addition, evidence for yawn contagion has been
reported among African elephants [40],
domesticated sheep [41], and elephant
seals [42]. Outside of mammalian
species, yawn contagion has also been documented
in birds. In particular, budgerigars have been
shown to yawn in response to both live
demonstrators and visually recorded conspecifics
[43,44]. However, a recent study found
no evidence for contagious yawning among
juvenile ravens [23].
Interspecific yawn contagion, whereby a yawn
from one species elicits contagion in another
species, has also been documented among some
animals in captivity. In particular, chimpanzees
have been shown to yawn in response to yawns
from humans [45]. In one study, it was
found that chimpanzees yawned contagiously both
in response to yawns from humans and in-group
chimpanzees, but not to out-group chimpanzees or
gelada baboons, which has been interpreted as a
sign of empathy [46]. However, other
great apes fail to show this type of
human-initiated yawn contagion, despite evidence
for an intraspecific effect [33].
Chimpanzees have also been shown to yawn in
response to yawns of computer animations of
conspecifics [29], while orangutans do
not show this reaction [32]. A recent
paper also found evidence for interspecific yawn
contagion among red-capped mangabeys, whereby
individuals yawned more in response to
conspecifics and familiar human caretakers
compared to unfamiliar species (i.e., hamadryas)
[47].
Domesticated dogs have also been reported to
yawn contagiously in response to human yawns
[48], which is noteworthy given that
domesticated dogs fail to show intraspecific
yawn contagion [49]. This discrepancy in
the stimulus trigger for this response in dogs
could be a result of an emphasis placed on
attending to human social cues during
domestication and selective breeding. A number
of follow-up studies have replicated the
presence of interspecific contagious yawning
among dogs, with some evidence suggesting that
empathy, as measured by the degree of
familiarity and/or social closeness to the human
yawner, enhances this response [50,51].
However, not all studies on domesticated dogs
have demonstrated this type of social effect
[52,53].
African elephants have also been shown to
yawn contagiously in response to yawns from
humans [54]. In particular, this study
found that three out of seven captive elephants
yawned following live yawns from familiar human
handlers. Again, the authors propose that this
behavior reflects a form of empathic processing
[54]. It is important to note, however,
that the connection between contagious yawning
and empathy is far from clear [55], and
attention towards the yawning stimuli&emdash;in
this case the familiar human
model(s)&emdash;could be driving this response
[56].
Current Study
To date, there have been no studies
examining interspecific contagious yawning in
humans. Therefore, this study sought to provide
the first formal investigation of whether people
yawn in response to yawns from non-human
animals. Given that this phenomenon occurs in
other species, and contagious yawning has proven
to be a reliable phenomenon in psychological
research [5,24,26,57], we predicted that
humans would also show interspecific yawn
contagion when compared to a control condition.
Moreover, this study aimed to test whether this
response was influenced by phylogenetic
relatedness and domestication/social closeness.
Consequently, comparisons were made between the
occurrence and frequency of contagious yawning
between participants that were shown yawning
stimuli from the following taxonomic groupings
of animals: fish, amphibians, reptiles, birds,
and non-primate mammals. To more closely examine
the factors of phylogeny and
domestication/social closeness, yawn contagion
was also measured from participants that were
displayed images of yawns from apes&emdash;the
closest living relatives to humans&emdash;and
common household pets: domesticated dogs and
cats.
Previous studies have shown that humans have
a biased perception of other animals based on
phylogenic relatedness, which may be predictive
of yawn contagion. For example, people tend to
demonstrate both higher subjective self-report
and psychophysiological measures of empathy
towards species with greater phylogenetic
proximity to humans [58].
Research has also shown that the perceived
communicative and empathic ability of a given
animal is positively correlated with the
phylogenetic relatedness to humans [59].
Similarly, in a large sample of participants in
the United States, Callahan et al. [60]
revealed that mammals were ranked highest among
traits characterized as cognitive and emotive,
followed by birds, reptiles, amphibians, and
then fish. Based on this literature, and the
proposed connections between yawn contagion and
empathy or emotional contagion [61,62],
we predicted that interspecific contagious
yawning in humans would be higher in response to
species that were more closely related (apes
> non-primate mammals > reptiles and birds
> amphibians > fish).
In addition, similar to some studies of
non-human animals [63], familiarity
biases for yawn contagion have previously been
demonstrated in humans. In particular,
observational studies report that people are
more likely to yawn in response to the yawns of
kin and friends compared to acquaintances and
strangers [64,65]. Whether the variation
in this response is driven by social/emotional
closeness or enhanced attention towards people
we know and care about remains unclear
[56], but the effect is robust.
Likewise, many of the studies on interspecific
contagious yawning in captive non-human animals
have been linked to some degree with empathy
and/or social closeness to human owners and
handlers [46,47,50,51]. Therefore, since
people tend to form strong bonds and attachments
with their pet cats and dogs [66,67,68],
we also predicted that contagious yawning would
be high in the pet condition.
Lastly, given that physiological variables
known to alter spontaneous yawning also modulate
yawn contagion [27], we also
hypothesized that participant tiredness at the
time of testing would predict interspecies
contagious yawning. Relatedly, based on the
association between yawning and sleep/wake
cycles [7,8,9,10], we also took into
account the duration of the sleep the night
prior to testing. Lastly, participant age and
gender were also collected since some studies
have shown these variables can affect
intraspecific yawn contagion
[69,70,71].
Discussion
Contagious yawning is well-documented in
both naturalistic and experimental studies on
humans [5,24,57,65,77], and emerges
during early childhood development [78].
While previous comparative research has provided
evidence for interspecific, i.e.,
human-initiated, contagious yawning in
chimpanzees [45,46], red-capped
mangabeys [47], domesticated dogs
[48,50,51,53], and African elephants
[54], to date, there have been no
studies examining whether humans yawn
contagiously in response to non-human
animals.
The current findings provide strong support
for interspecific contagious yawning in humans.
The tendency to yawn was significantly higher in
each of the interspecific yawning conditions
compared to the control (non-yawning) condition.
The same was true for overall yawn frequency,
except in the case of the amphibian and mammal
conditions. The attentional checks to the
pairing of yawn and non-yawning stimuli produced
a robust response, with a comparably high rate
of yawn contagion (69%) to a recent online study
on intraspecific yawn contagion using compiled
video clips [27]. Contrary to our
predictions, however, neither phylogenetic
proximity nor domestication/social closeness of
the yawning stimuli enhanced this response. In
fact, there was a complete absence of any trend
consistent with these hypotheses (Figure 1 and
Figure 2). Since previous work has shown that
people tend to have higher levels of empathy
towards species with greater phylogenetic
proximity [58], these findings do not
support the view that contagious yawning is
linked with empathy or emotional contagion
[46,63,64,65]. Instead, the current
results suggest that the mechanisms governing
yawn contagion in humans are generalized, and
can be triggered by varied representations of
yawning across diverse taxa. Likewise, since the
inclusion criteria for this study required
stringent attention checks towards the yawning
stimuli, these findings are consistent with the
position that variation in yawn contagion is
driven by detection of the yawning stimulus
[55,56].
Similar to most studies of intraspecific
contagious yawning [79], participant
gender was not a significant predictor of
interspecific yawn contagion. However, as
predicted, participants that were more tired at
the time of testing reported both a higher
incidence and a greater overall frequency of
yawning. The fact that tiredness was the best
predictor of yawn contagion in this study
replicates recent research on intraspecific
contagious yawning in humans [27] and
further supports previous studies showing that
contagious yawns are modulated by physiological
factors known to trigger spontaneous yawning
[8,80,81,82,83].
While this study provides novel results and
an improved understanding of contagious yawning,
there are limitations that should be
acknowledged. First, only twelve yawning images
were included in each interspecific condition,
and with the exception of the apes, this only
represented a small proportion of species
diversity within the taxonomic groupings.
Therefore, it remains possible that different
species and/or representations of yawning could
produce different results. However, we find this
unlikely given the complete absence of any trend
for phylogenetic proximity or domestication
increasing contagion. Nonetheless, future
research could be conducted to potentially
identify species that elicit stronger or weaker
responses. For example, based on this study, we
could not assess whether contagion in the pet
condition differed between cat and dog stimuli.
The online nature of this study is another
limitation, as it relied on self-reported
contagious yawning from respondents using MTurk.
However, previous studies with diverse
methodologies have shown that self-report is a
valid measure of contagious yawning
[25,84,85]. In addition, the attention
check questions used when evaluating the stimuli
exceed typical attentional measures in studies
on yawn contagion in humans and, thus, represent
a strength of the current research. In
particular, this method ensured that all yawning
stimuli were actually detected, rather than
attention being directed towards the stimulus
images in general. That said, we hope this
initial study spurs follow-up research in this
area.
Conclusions
In summary, this research provides the first
evidence for interspecific contagious yawning in
humans. Contrary to our predictions, the results
show that this response was not enhanced by
phylogenetic proximity or domestication/social
closeness. Instead, these findings suggest that,
when controlling for attention, the mechanisms
governing yawn contagion can be activated by
varied forms of yawning stimuli, including those
from distantly related and unfamiliar species.
