This study is the first to demonstrate that
human yawns are possibly contagious to domestic
dogs (Canis familiaris). Twenty-nine dogs
observed a human yawning or making control mouth
movements. Twenty-one dogs yawned when they
observed a human yawning, but control mouth
movements did not elicit yawning from any of
them. The presence of contagious yawning in dogs
suggests that this phenomenon is not specific to
primate species and may indicate that dogs
possess the capacity for a rudimentary form of
empathy. Since yawning is known to modulate the
levels of arousal, yawn contagion may help
coordinate dog-human interaction and
communication. Understanding the mechanism as
well as the function of contagious yawn- ing
between humans and dogs requires more detailed
investigation. Keywords: yawning; contagious
yawning; dog; empathy; social cognition
1. Introduction
Contagious yawning (i.e. yawning triggered
by perceiv- ing others yawning) is a
well-documented phenomenon (e.g. Moore
1942; Provine
1986; Platek
et al. 2003; Senju
et al. 2007). Although some claim that
contagious yawning is a response to an innate
releasing mechanism ( Provine 1986), the
relationship between the susceptibility to
contagious yawning and self- reported scores of
empathy ( Platek et al. 2003), as well as the
absence of contagious yawning in individuals
with autism spectrum disorder (Senju et al.
2007), suggests that it may be related to the
capacity for empathy ( Preston
& de Waal 2002).
Even though spontaneous yawning is
widespread among vertebrate species (Baenninger
1987; Heusner
1946), contagious yawning has been reported to
occur only in humans and chimpanzees (Pan
troglodytes; Anderson et al. 2004). Stumptail
macaques (Macaca arctoides) also yawn in
response to observed yawns, although it is
unclear whether this behaviour is similar to
contagious yawning found in other species or
simply reflects stress ( Paukner
& Anderson 2006).
The current study examined whether
contagious yawning can be observed in domestic
dogs (Canis familiaris). Dogs are unusually
skilled at reading human social and
communicative cues. They can follow human gaze
and pointing ( Hare et al. 2002; Miklosi et al.
2003; Miklosi & Soproni 2006), they can show
sensitivi ty to other's knowledge states (e.g.
indicating the location of a hidden toy more
frequently to someone not involved in hiding it
than to someone who did the hiding, Viranyi et
al. 2006) and they are even able to match their
own actions to obser ved human actions ( Topal
et al. 2006). Dogs' unique social skills in
interacting with humans may be the result of
selection pressures during the process of
domestication ( Hare & Tomasello 2005;
Miklosi et al. 2003, 2007).
Therefore, there is the potential that dogs
may also have devel oped the capacity f or
empathy towards humans, and may catch human
yawns. However, no empirical studies have been
reported, which systematically investigate
contagious yawning in dogs. In the current
study, dogs observed a human experimenter
yawning (yawning condition) or demonstrating
non-yawning mouth movements (control condition).
If dogs have the capacity for contagious
yawning, they should yawn more in the yawning
condition than in the control condition.
4. Discussion
The current study demonstrates that human
yawns are possibly contagious to dogs. The
presentation of human yawning elicited yawns in
72 per cent of the dogs tested, which is higher
than the rate reported in humans (45-60%) and
chimpanzees (33%). This effect cannot be
attributed to a general effect of the mere
presence of unf amiliar humans, or to the obser
vation of human mouth movements in general,
because no dogs yawned in the control
condition.
This study is the first to demonstrate that
the obser vation of yawning elicits yawning in a
non-primate species, as well as the first
demonstration of possible contagious yawning
between different species. Since yawning is
known to modulate the level of arousal (Daquin
et al. 2001), such temporally synchronized
occurrences of yawning may help coordinate
interactions as well as communication between
humans and dogs.
The high yawning rate may be due to
displaying "live" acted yawns rather than
video-recorded yawns that have been used in some
previous studies (Anderson et al. 2004; Paukner
& Anderson 2006; Senju et al. 2007). It is,
however, highly unlikely that the present
results could be influenced by the experimenter
unintentionally reinforcing dog's yawning in the
yawning condition.
The main analysis is based on dichotomous
data (i.e. the dog yawned or did not yawn in
each condition). Reinforcement of chance yawns
could only account for a difference in absolute
number of yawns per dog, and not the presence/
absence of yawns for a dog in each condition.
There are at least two possibilities why human
yawns elicit yawning in dogs.
First, the susceptibility to contagious
yawning of dogs may relate to their capacity for
empathy. In humans ( Platek et al. 2003; Senju
et al. 2007) and chimpanzees (Anderson et al.
2004), several studies have suggested that
contagious yawning relates to the capacity for
empathy, although the mechanism underlying this
relationship is still unclear. As described
above, dogs have exceptional capacities to
decode social signals from humans, possibly as a
result of the domestication process ( Hare &
Tomasello 2005; Miklosi et al. 2003, 2007).
Therefore, it is also possible that they have
the capacity for empathy, such as representing
humans' actions and modulating their own
behavioural and autonomic responses accordingly
(see also Topal et al. 2006), and that this
underlies contagious yawning.
Alternatively, dogs may have developed the
capacity for contagious yawning during past
synchronous yawning experiences with humans
(e.g. Heyes & Ray 2000), either by sharing
(e.g. boring) experiences with humans or by
observing human's yawns contagiously to dog's
yawns.
Second, it is also possible that the dogs'
yawns may have been induced by mildly heightened
tension or stress. For example, macaques are
known to exhibit "emotion yawns" or "social
yawns" during antagonistic social encounters (
Deputte
1994; Smith 1999;
Paukner & Anderson 2006). Thus, we cannot
rule out the possibility that human yawns are
perceived as antagonistic to the dogs.
Previous studies have demonstrated that dogs
may yawn in response to an encounter with novel
humans (Beerda et al. 1998; Hennessy et al.
2006). Some have argued that it is a response to
acute stress (Beerda et al. 1998), althoughth is
argument is not supported by more recent
empirical studies (e.g. Hennessy et al. 2006;
Rooney et al. 2007).
However, as physiological measurements of
stress, such as saliva/blood cor tisol or heart
rate, were not available f or t he current
sample, and because there has not been enough
consensus and standardization on how to
interpret dogs' behaviours ( Diederich &
Giffroy 2006), further studies, ideally with
concurrent physiological measurements, are
required to test whether contagious yawning
between humans and dogs is mediated by a stress-
or tension- related response.
At least, the current results cannot be
attributed to more general factors related to
stress, such as an encounter with a strange
human or to the recording equipment, as no dogs
yawned in the control condition.
Although the current study cannot
discriminate between these two possible
explanations, fur ther studies could explore the
mechanism underlying, as well as the evolutionar
y origin of contagious yawning and its
relationship to the capacity for empathy.
For example, the current study demonstrated
that dogs appear to catch human yawns. However,
for practical reasons, we did not examine
whether they yawn contagiously to conspecifics'
yawns.
If the dogs' capacity for contagious yawning
has evolved with the capacity for reading human
communicative signals, it is possible that dogs
are more sensitive to human yawns than dogs'
yawns.
By contrast, if they have acquired the
capacity for contagious yawning as an adaptation
for within-species social interaction and
communication, which has transferred to
dog-human interaction, they may be more
sensitive to the yawns of conspecifics. Such
contrasts may help highlight the functional
specialization of contagious yawning in dogs
and, possibly, in other species as well.
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In: Kusonose, Ryo and Sato, Shusuke 39th
Congress of the International Society for
Applied Ethology, Kanagawa, Japan. 20-24 August,
2005
