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Paedomorphic Facial Expressions Give Dogs a Selective Advantage


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How wolves were first domesticated is unknown. One hypothesis suggests that wolves underwent a process of self-domestication by tolerating human presence and taking advantage of scavenging possibilities. The puppy-like physical and behavioural traits seen in dogs are thought to have evolved later, as a byproduct of selection against aggression. Using speed of selection from rehoming shelters as a proxy for artificial selection, we tested whether paedomorphic features give dogs a selective advantage in their current environment. Dogs who exhibited facial expressions that enhance their neonatal appearance were preferentially selected by humans. Thus, early domestication of wolves may have occurred not only as wolf populations became tamer, but also as they exploited human preferences for paedomorphic characteristics. These findings, therefore, add to our understanding of early dog domestication as a complex co-evolutionary process.
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Paedomorphic Facial Expressions Give Dogs a Selective
Bridget M. Waller
*, Kate Peirce
´tia C. Caeiro
, Linda Scheider
, Anne M. Burrows
, Sandra McCune
Juliane Kaminski
1Centre for Comparative and Evolutionary Psychology, University of Portsmouth, Portsmouth, Hampshire, United Kingdom, 2Department of Psychology, Freie Universita
Berlin, Berlin, Germany, 3Department of Physical Therapy, Duquesne University, Pittsburgh, United States of America, 4Department of Anthropology, University of
Pittsburgh, Pittsburgh, United States of America, 5WALTHAMH, Centre for Pet Nutrition, Leicestershire, United Kingdom
How wolves were first domesticated is unknown. One hypothesis suggests that wolves underwent a process of self-
domestication by tolerating human presence and taking advantage of scavenging possibilities. The puppy-like physical and
behavioural traits seen in dogs are thought to have evolved later, as a byproduct of selection against aggression. Using
speed of selection from rehoming shelters as a proxy for artificial selection, we tested whether paedomorphic features give
dogs a selective advantage in their current environment. Dogs who exhibited facial expressions that enhance their neonatal
appearance were preferentially selected by humans. Thus, early domestication of wolves may have occurred not only as
wolf populations became tamer, but also as they exploited human preferences for paedomorphic characteristics. These
findings, therefore, add to our understanding of early dog domestication as a complex co-evolutionary process.
Citation: Waller BM, Peirce K, Caeiro CC, Scheider L, Burrows AM, et al. (2013) Paedomorphic Facial Expressions Give Dogs a Selective Advantage. PLoS ONE 8(12):
e82686. doi:10.1371/journal.pone.0082686
Editor: Claire Wade, University of Sydney, Australia
Received July 8, 2013; Accepted October 27, 2013; Published December 26, 2013
Copyright: ß2013 Waller et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The study was funded by a WALTHAM Foundation Research Grant to BMW, JK and AB. The funder had some input during study design, but did not
influence study findings, interpretation of results or writing of the manuscript. The funder had some input during study design, but did not influence study
findings, interpretation of results or writing of the manuscript.
Competing Interests: The authors declare that author SM is an employee (Research Manager) of WALTHAM, a division of Mars Inc. All other authors have
declared that no competing interests exist. This does not alter their adherence to all the PLOS ONE policies on sharing data and materials.
* E-mail:
Wolves were domesticated early in the history of human
civilization [1], and have since evolved into dogs whose lives are
now inextricably linked to those of humans. The initial steps that
led to wolves becoming domesticated, however, is unknown. One
hypothesis suggests that wolves underwent a process of self-
domestication as tamer individuals took advantage of opportuni-
ties to scavenge from human settlements during the agricultural
revolution [2]. In support of this theory is recent evidence that
domestic dogs exhibit genetic mutations to a starch-rich diet [3].
During domestication, dogs have departed from wolves on various
other behavioral and physical dimensions [2,4,5], one of the most
striking being paedomorphism. In many ways dogs appear more
like wolf puppies than wolf adults. These features are thought to
have evolved as a byproduct of the domestication process, and
arose accidently when aggression was actively selected against
[6,7], for a detailed review see [8].
Paedomorphic features, however, could have evolved much
earlier in response to human preferences. Domestic cats have
developed modified purr vocalizations that appear to solicit
increased care from human hosts by mimicking human infant
cries [9], and which may have increased tolerance of cats in
human environments during domestication. Likewise, the
shorter snout and wider cranium of the dog give the dog face
a more puppy like appearance (although there is variation
between breeds) which may have evolved as the well
documented human preference for paedomorphic facial char-
acteristics [10] was exploited. Paedomorphic facial features can
be further enhanced through use of upper face facial muscle
contractions that lift the brow to increase the apparent height
and overall size of the orbital cavity (i.e. the apparent size of the
eyes: figure 1). Large eyes relative to the rest of the face are a
prominent feature in human infants and are associated with
perceived cuteness of and motivation to invest in human infants
by human adults [10,11]. Toys (teddy bears) that display this
trait are also preferred [12,13]. Infantile facial features are
similarly preferred in pet dogs and cats [14], and manipulation
of infant-like facial traits increases perceived cuteness [15].
However, in all of these studies humans are making forced
choices in experimental conditions. In addition, demonstrating
visual preference does not necessarily mean that these animals
are (or have been) selected preferentially. To demonstrate
whether these human preferences translate into differential
investment we need to examine which dog characteristics incur
a current selective advantage. Current fitness is not necessarily
indicative of past selection of course, but it is a common
assumption in behavioural ecology and evolutionary anthropol-
Juvenile traits other than face may have also been subject to
selection, of course. Tail wagging and other submissive behaviours
are more common in wolf puppies than adult wolves but persist in
the adult dog [5], and are more often human directed [16]. Such
behaviours, however, are not human-like or even universally
mammalian, so it is unlikely that they would be as salient as the
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face (to humans), which is widely understood to be an attention
grabbing stimulus in both humans and other animals.
Dog facial expressions have been described in classic studies
[17], but as the facial muscles of social mammals (including
humans) can exhibit great subtlety of movement, standardised
methods for facial movement measurement are needed to make
accurate observations within and between species. Scientists must
use validated, anatomically based systems for recording facial
expression. First, facial expressions are processed as whole units in
an automatic, streamlined manner which makes it difficult to see
the detail accurately [18]. Second, human observers tend to
categorise facial expressions in terms of emotion, which can affect
how comparisons between species are made [19]. The Facial
Action Coding System (FACS: [20]) is an anatomically based
facial expression coding system used in humans to counter these
problems, which identifies observable facial changes associated
with underlying muscle movement. Recently, the system has been
successfully modified for use with chimpanzees [21], rhesus
macaques [22], hylobatids [23] and orangutans [24]. The systems
are objective, reliable and standardised, and allow subtle
movements to be identified and quantified.
In the current study we used shelter dog rehoming as a proxy
for dogs’ selection over time. We tested whether humans (when
adopting dogs from a shelter) actively select for dogs, which appear
more juvenile in the face as a result of facial muscle contraction.
AU101 (inner brow raiser) raises the medial portion of the brow
increasing the apparent size of the eyes in relation to the face, and
as such enhances one of the features of the face associated with
infants. Subtle facial muscle movements were recorded using an
anatomically based facial muscle coding system (DogFACS). We
examined whether frequent use of these movements (AU101:
inner brow raiser) was associated with selection by humans using
real world shelter dog adoption speed as a proxy for human
selection over evolutionary time.
Materials and Methods
Ethics Statement
This study was carried out in strict accordance with the
recommendations in the ASAB/ABS guidelines for the use of
animals in research and was approved by the University of
Portsmouth Animal Ethics Committee.
Development of DogFACS
Footage from 28 privately owned dogs of varying breeds
(approximately 8–10 hours) from the Max Planck Institute for
Evolutionary Anthropology DogLab was the primary source for
DogFACS development. In addition, we sourced approximately
100 clips from (permission granted from the
copyright holder of each clip) and used ad hoc footage from 86
dogs at four dog shelters (Portsmouth City Dog Kennels; Wood
Green, The Animal’s Charity in Cambridge; The Dog’s Trust,
West London, Harefield and RSPCA Southridge Animal Centre,
London). Each facial movement was documented by appearance
changes, minimal criteria for identification and comparison to
other species, in line with FACS terminology (Table 1). The
muscular basis of each facial movement was verified in light of
dissection of a face from a specimen of a domestic dog (AMB) as
well as previously published dissections [25]. The manual is freely
available and requires certification to use (
Shelter Dog Data Collection
The study used a correlational design using data from a one-
shot, timed observation. Dogs were observed at the same four re-
homing shelters (above). The modal breed group (bull breeds,
which includes all breeds derived from the molasser breed,
Staffordshire Bull Terriers, Mastiffs and mixed bull breeds: as
classified by the shelter staff using criteria from the UK Kennel
Club) was chosen for analysis to minimise the variance associated
with breed differences, and totalled 29 dogs. Each dog was filmed
Figure 1. Example of facial movement AU101 (inner brow raiser) in a domestic dog (Rhodesian Ridgeback, not a subject in the
study), increasing the height and overall size of the orbital cavity (eye): A) neutral on right side of face, B) AU101 on right side of
Paedomorphic Facial Expressions in Dogs
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for a 2 min period (focal sampling) during controlled first contact
with the experimenter. The experimenter approached the subject’s
kennel room and stood in front of the room with a neutral stance
and holding out one hand. Each 2 min video sample (from each
dog subject) was coded using DogFACS to record the frequency of
facial movements (full DogFACS coding), duration of tail wagging
and time spent at the front of the kennel in close proximity to the
experimenter. The number of days between becoming available
for re-homing and leaving the shelter was recorded. Reliability
assessment was conducted on the behavioural coding (DogFACS
AUs and other behaviours: Table 2) for 30% of the sample (8 dogs)
using Wexler’s Agreement (Ekman et al., 2002):
Table 1. Comparison of action units (AUs) and the underlying facial muscles in humans [20] and dogs.
Action Units Facial Musculature
Humans Dogs Humans Dogs
Upper Face
1Inner brow raiser 101 Inner brow raiser Frontalis (medial) Frontalis is present but it does not seem
to raise the brow region. Levator anguli
occuli medialis raises the inner brow
2Outer brow raiser Not observed Frontalis (lateral) (As above)
4Brow lowerer Not observed Procerus, corrugator supercilii,
depressor supercilii
Not present
5Upper lid raiser Not observed Levator palpebrae superioris Not described
6Cheek raiser Observed only with 143 and 145 Orbicularis occuli Present
7Lid tightener Not observed (As above) (As above)
43 Eye closure 143 Eye closure Relaxation of levator palpebrae
Orbicularis occuli
45 Blink 145 Blink (As above) (As above)
Lower Face
9Nose wrinkler 109+110 Nose wrinkler and upper lip
raiser - nose wrinkler hard to code
Levator labii superioris
alaeque nasi
Levator nasolabialis, caninus, levator
labii maxillaris
10 Upper lip raiser 110 Upper lip raiser Levator labii superioris (As above)
11 Nasiolabial furrow deepener Not observed Zygomaticus minor Not present
12 Lip corner puller 12 Lip corner puller Zygomaticus major Zygomaticus
13 Sharp lip puller Not observed Caninus Present
14 Dimpler Not observed Buccinator Present
15 Lip corner depressor Not observed Depressor anguli oris Not present
16 Lower lip depressor 116 Lower lip depressor Depressor labii inferioris Platysma
17 Chin raiser Not observed Mentalis Present
18 Lip pucker 118 Lip pucker Incisivii labii (superioris and
inferioris), orbicularis oris
Only orbicularis oris present
20 Lip stretcher Not observed Risorius Not present
22 Lip funneler Not observed Orbicularis oris Present
23 Lip tightener Not observed Platysma Present
24 Lip presser Not observed Orbicularis oris Present
25 Lips part 25 Lips part Orbicularis oris, depressor labii
inferioris, levator labii superioris
Orbicularis oris, caninus, levator labii
maxillaris, levator nasolabialis, platysma
26 Jaw drop 26 Jaw drop Non-mimetic muscles: masseter, temporalis, pterygoid and digastricus
27 Mouth stretch 27 Mouth stretch (As above)
Action Units Facial Musculature
Humans Dogs Humans Dogs
Miscellaneous Action Units
8Lips towards each other Not observed Orbicularis oris Present
21 Neck tightener Not observed Platysma Present
38 Nostril dilator Observed during sniff (AD40) Nasalis Not present
39 Nostril compressor (As above) (As above) (As above)
Paedomorphic Facial Expressions in Dogs
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2(#AUs on which Coder 1 and Coder 2 agreed)
total #of AUs scored by the two coders
Proximity and tail wagging were treated as categorical variables
by using number of bouts instead of overall duration for the
reliability and agreement was also assessed using Wexler’s
Table 2. Wexler’s agreement calculations for the behavioural
Behaviour Agreement
EAD101 (ears forward) 0.69
EAD102 (ears adductor) 0.79
EAD103 (ears flattener) 0.73
EAD104 (ears rotator) 0.83
AU101 (inner brow raiser) 0.78
AD19 (tongue show) 0.71
AD137 (nose wipe) 0.86
AU25 (lips parted) 0.91
AU26 (jaw drop) 0.88
Proximity 1.00
Tail wagging 0.76
Figure 2. Relationship between frequency of AU101 and days before re-homing in the dog shelter. Curved line shows the power
Table 3. Relationship between behaviours exhibited during
the 2 min observation period and the number of days before
Behaviour Days before re-homing
Spearman’s rho p value
#AU101 (inner brow raise) 2.501 .008
#AU19 (tongue show) .070 .729
#AD137 (nose wipe) .339 .083
#AU25 (lips parted) .262 .187
#AU26 (jaw drop) .268 .176
#EAD101 (ears forward) 2.331 .091
#EAD102 (ears adductor) 2.236 .236
#EAD103 (ears flattener) 2.187 .349
#EAD104 (ears rotator) 2.005 .981
Tail wagging duration .424 .027
Time at front of kennel 2.393 .042
Age (months)
.153 .474
N = 24 as age was unavailable for some dogs.
Paedomorphic Facial Expressions in Dogs
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Two dogs were removed as their time before re-homing was
greater than the upper quartile by more than 1.5 IQR (82+87
days), and thus were perceived to be outliers (and their long
stay most likely due to unusual factors). Our final sample
included 27 dogs for analysis (Age range = 7–96 months,
M= 29.46 months). Nonparametric correlations (as the depen-
dent variable was not normally distributed) were used to explore
the relationships between the behavioural variables and the
number of days before re-homing (Table 3). AU101 and time at
the front of the kennel were the only variables significantly
negatively correlated with days before re-homing, indicating that
dogs that produced more of these behaviours were re-homed
quicker. Tail wagging was positively correlated indicating that
dogs that tail wagged more were re-homed slower. Note,
however, that if Bonferroni corrections were applied, no
variables would be deemed significant so these exploratory
findings should be taken with caution. Visual inspection of
scatter plots and curve estimation were used to explore the
relationships further. Time spent at the front of the kennel and
tail wagging had very weak or no linear or curvilinear
relationships with the dependent variable. AU101 had a
significant power curve relationship with the dependent variable
and the model explained a significant proportion of the variance
in re-homing speed (R
= 0.39, F(1,25) = 15.63, p,0.005), see
Figure 2. From the regression equation (y = 114.12x
, see
Table 4) we can predict that a dog that produces five AU101
during the 2 min observation will stay in the shelter for 49.83
days on average, but if it produces 10 AU101, this would be
reduced to 34.88 days, and if it produces 15, this would be
reduced to 28.31 days. As there is a negative power relationship
the slope becomes less steep as AU101 increases, and so the
benefit (in terms of re-homing) in producing AU101 reduces
with increasing AU101.
Domestic dogs who produced a high frequency of facial
movement to raise the inner brow (AU101) were adopted more
quickly from re-homing shelters. As AU101 enhances a key
feature of paedomorphism (eye size and height: [10]) this
suggests that dogs have evolved to manipulate the human
preference for paedomorphic features using the face. This is the
first empirical evidence that paedomorphism plays a key role in
humans’ current selection of dogs, and the first time that actual
investment has been used as an indicator of preference. If the
selection process in the shelter context emulates past selection
during domestic dog evolution, this preference may have also
been at work during early dog domestication.
Interestingly, tail wagging and close proximity to the human
were not strongly associated with speed of selection by adopters,
despite being factors that are commonly believed to indicate a
friendly temperament. In fact, higher durations of tail wagging
resulted in a longer period before re-homing. This finding
further supports the growing evidence that indirect manipulation
of human sensory preferences (particularly a preference for
juvenile facial characteristics) has been a particularly powerful
selective force in domestication [2,9], even more so than
genuine indicators of temperament. Importantly, it is highly
possible that these facial expressions do not correlate with
suitability as a pet, but, like superficial morphological traits, are
still preferred over more relevant behavioural traits [26].
In humans, the equivalent facial movement to AU101 is
AU1(inner brow raiser), which features heavily in human
sadness expressions [20]. It is possible, therefore, that human
adopters were responding not to paedomorphism, but instead to
perceived sadness in the dogs looking for adoption. However, it
is also possible that the human sadness expression is itself
derived from paedomorphism, and that sadness is attributed to
this specific facial movement because it enhances paedomorphism
and thus perceived vulnerability. Another possibility is that
humans are responding to the increase in white sclera exposed
in the dogs as the orbital cavity is stretched through AU101
action. Visibile sclera is a largely unique human trait [27]
(which likely contributes to our extensive gaze following abilities)
and people are more likely to cooperate or behave altruistically
when exposed to cues of being watched [28,29]. It is unclear,
however, whether it is the sclera specifically or simply the
presence of eyes per se which has such a powerful affect on
human behavior and attention, and so this is more a
complimentary hypotheses as opposed to an alternative.
Our real world data show that domestic dogs who exhibit
paedomorphic characteristics are preferentially and actively
selected by humans as pets from rehoming shelters. This
therefore supports the hypothesis that paedomorphic character-
istics in domestic dogs arose as a result of indirect selection by
humans rather than only being a by-product of selection against
aggression. Whether our findings are transferable to other
contexts, such as breeding, is unknown, and it is possible that
modern breeding practices put emphasis on such specific
morphological and behavioural traits that this effect is obscured.
However, given that recent evidence leans towards early wolf
domestication arising from tolerance of their presence rather
than direct selection per se [2,3], adoption from shelters might
be a more appropriate proxy than modern breeding. We can
therefore speculate that early domestication of wolves may have
occurred not only as wolf populations became tamer [2,3], but
also as they exploited human preferences for paedomorphic
Supporting Information
Raw Data S1 The raw data.
We would like to thank the following for access to their shelter dogs:
Portsmouth City Dog Kennels; Wood Green, The Animal’s Charity in
Cambridge; The Dog’s Trust, West London, Harefield and RSPCA
Southridge Animal Centre, London. We thank Jamie Whitehouse for
reliability coding. We also thank Alison Colyer (Statistics Team,
WALTHAMH) and Ed Morrison for helpful comments on the statistics,
and two anonymous reviewers for constructive help revising the
Table 4. Regression statistics (power curve fit) between
AU101 and the number of days before re-homing, showing
unstandardised co-efficients (B) and the associated standard
error (SE B), standardised co-efficients (b) and significance
values (P).
(Constant) 114.12 30.26
AU101 2.52 .13 2.62 .001
Paedomorphic Facial Expressions in Dogs
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Author Contributions
Conceived and designed the experiments: BMW AMB JK. Performed the
experiments: KP CCC LS. Analyzed the data: BMW. Contributed
reagents/materials/analysis tools: AMB. Wrote the paper: BMW JK.
Assisted with study design: SM.
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Paedomorphic Facial Expressions in Dogs
PLOS ONE | 6 December 2013 | Volume 8 | Issue 12 | e82686
... Dogs possess a wide repertoire of signals to interact with the environment and communicate their responses to different situations [1]. They can express themselves through facial expressions [2][3][4], which are sensitive to human attentional state [5], body posture [6,7], tail wagging [8] and vocalisations [9,10]. They are able to do so in distinctive ways depending on the emotional salience of a stimulus (positive or negative) that they are responding to. ...
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Dogs are good models for studying behaviour and cognition as they have complex social capabilities. In the current study, we observed how human emotional valences (positive, neutral and negative) affected aspects of dogs’ behaviour. We expected that dogs would exhibit more approaching behaviours in the positive condition and more signs of avoidance in the negative one. We analysed videos of 70 adult pet dogs of various breeds taken from an experiment in which one of two actors expressed an emotion and dogs could freely explore the environment for 30 s. Our results show that dogs exhibit differential behaviour when presented with different emotional valences. Two behaviours arose that might be linked to a reciprocal positive emotional state in dogs: tail raised between 90° and 180° and physical contact during sniffing. These behaviours are associated with an active search for information. In the positive conditions, dogs were more willing to explore the social environment and gather information from the actors.
... [33][34][35] . Paedomorphic facial attributes have been found to enhance the chance of adoption in both cats 36 and dogs 37 . Owners also infer the personality of dogs and expected relationship quality based on physical appearance 38 . ...
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Despite the serious problems with their general health and longevity, small brachycephalic breeds, especially the French bulldog, are becoming increasingly popular among pet owners. The motivations for the choice of short-nosed breeds have been extensively investigated in recent years; however, this issue has been addressed mainly by relying on owner reports, resulting in somewhat vague explanations of "cute looks", referring to the child-schema phenomenon and "behaviour well suited for companionship". In this study, we set out to compare the behaviour of two brachycephalic (English and French bulldogs) and a mesocephalic (Hungarian mudi) breed in a problem-solving context. The dogs were given the task of opening boxes containing food rewards. We investigated human-directed behaviour elements over success and latency (indicators of motivation and ability). ... We found that the short-headed breeds were less successful but much more oriented toward humans than mesocephalic dogs. Owners might interpret these behaviours as "helplessness" and dependence. The results support the hypothesis that infant-like traits may be present not only in appearance but also in behaviour in brachycephalic breeds, eliciting a caring behaviour in owners.
... It takes a human approximately 100 hours to learn how to code photographs or videos into FACS units by visual changes alone; however, modern research now includes computer programs that auto-code video (32). FACS has since been adapted to the human infant (33) and various animal (34,35) physiology. ...
... Besides these similarities, there are important differences between human infants' and family dogs' cognitive abilities and emotional processing. Dogs are non-conspecific social partners with different anatomy and the capacity to display facial expressions as compared to humans 36,37 . There is also evidence that they process human faces differently than humans do (e.g. ...
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Parents tend to use a specific communication style, including specific facial expressions, when speaking to their preverbal infants which has important implications for children’s healthy development. In the present study, we investigated these facial prosodic features of caregivers with a novel method that compares infant-, dog- and adult-directed communication. We identified three novel facial displays in addition to the already described three facial expressions (i.e. the ‘prosodic faces’) that mothers and fathers are typically displaying when interacting with their 1–18 month-old infants and family dogs, but not when interacting with another adult. The so-called Special Happy expression proved to be the most frequent face type during infant- and dog-directed communication which always includes a Duchenne marker to convey an honest and intense happy emotion of the speaker. These results suggest that the ‘prosodic faces’ play an important role in both adult-infant and human–dog interactions and fulfil specific functions: to call and maintain the partner’s attention, to foster emotionally positive interactions, and to strengthen social bonds. Our study highlights the relevance of future comparative studies on facial prosody and its potential contribution to healthy emotional and cognitive development of infants.
... Some adults have also been noted to interpret dog behavior in this way (Demirbas et al., 2016). Because of their paedomorphic, or baby-like, features (Waller et al., 2013;Kaminski et al., 2019), dog facial configurations are often perceived as cute, which may result in humans giving a positive appraisal when interpreting canine behavior (Borgi et al., 2014;Borgi & Cirulli, 2016). ...
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Personal wellbeing is greatly influenced by our childhood and adolescence, and the relationships formed during those phases of our development. The human-dog bond represents a significant relationship that started thousands of years ago. There is a higher prevalence of dog ownership around the world, especially in households including children. This has resulted in a growing number of researchers studying our interactions with dogs and an expanding evidence base from the exploration of child-dog interactions. We review the potential effects of child-dog interactions on the physical, mental, and social wellbeing of both species. A search of the SCOPUS database identified documents published between January 1980 and April 2022. Filtering for key inclusion criteria, duplicate removals, and inspecting the references of these documents for additional sources, we reviewed a total of 393 documents, 88% of which were scientific articles. We were able to define the numerous ways in which children and dogs interact, be it neutral ( e.g ., sharing a common area), positive ( e.g ., petting), or negative ( e.g ., biting). Then, we found evidence for an association between childhood interaction with dogs and an array of benefits such as increased physical activities, a reduction of stress, and the development of empathy. Nonetheless, several detrimental outcomes have also been identified for both humans and dogs. Children are the most at-risk population regarding dog bites and dog-borne zoonoses, which may lead to injuries/illness, a subsequent fear of dogs, or even death. Moreover, pet bereavement is generally inevitable when living with a canine companion and should not be trivialized. With a canine focus, children sometimes take part in caretaking behaviors toward them, such as feeding or going for walks. These represent opportunities for dogs to relieve themselves outside, but also to exercise and socialize. By contrast, a lack of physical activity can lead to the onset of obesity in both dogs and children. Dogs may present greater levels of stress when in the presence of children. Finally, the welfare of assistance, therapy, and free-roaming dogs who may interact with children remains underexplored. Overall, it appears that the benefits of child-dog interactions outweigh the risks for children but not for dogs; determination of the effects on both species, positive as well as negative, still requires further development. We call for longitudinal studies and cross-cultural research in the future to better understand the impact of child-dog interactions. Our review is important for people in and outside of the scientific community, to pediatricians, veterinarians, and current or future dog owners seeking to extend their knowledge, and to inform future research of scientists studying dogs and human-animal interactions.
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Comparative studies of human–dog cognition have grown exponentially since the 2000’s, but the focus on how dogs look at us (as well as other dogs) as social partners is a more recent phenomenon despite its importance to human–dog interactions. Here, we briefly summarise the current state of research in visual perception of emotion cues in dogs and why this area is important; we then critically review its most commonly used methods, by discussing conceptual and methodological challenges and associated limitations in depth; finally, we suggest some possible solutions and recommend best practice for future research. Typically, most studies in this field have concentrated on facial emotional cues, with full body information rarely considered. There are many challenges in the way studies are conceptually designed (e.g., use of non-naturalistic stimuli) and the way researchers incorporate biases (e.g., anthropomorphism) into experimental designs, which may lead to problematic conclusions. However, technological and scientific advances offer the opportunity to gather much more valid, objective, and systematic data in this rapidly expanding field of study. Solving conceptual and methodological challenges in the field of emotion perception research in dogs will not only be beneficial in improving research in dog–human interactions, but also within the comparative psychology area, in which dogs are an important model species to study evolutionary processes.
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Brachycephalic dog breeds are highly popular, yet their conformation-related disorders represent a major welfare concern. It has been suggested that the current popularity of such breeds can be explained by their cute, infant-like facial appearances. The concept of ‘kindchenschema’ refers to the observation that certain physical features of infant humans and other animals can automatically stimulate positive and nurturant feelings in adult observers. But the proposal that brachycephalic dogs possess heightened ‘kindchenschema’ facial features, even into adulthood, has never been formally investigated. Here, we hypothesised that relative muzzle shortening across a range of breeds would be associated with known ‘kindchenschema’ facial features, including a relatively larger forehead, larger eyes and smaller nose. Relative fronto-facial feature sizes in exemplar photographs of adult dogs from 42 popular breeds were measured and associated with existing data on the relative muzzle length and height-at-withers of the same breeds. Our results show that, in adulthood, shorter-muzzled breeds have relatively larger (taller) foreheads and relatively larger eyes (i.e. area of exposed eyeball relative to overall face area) than longer-muzzled breeds, and that this effect is independent of breed size. In sum, brachycephalic dog breeds do show exaggeration of some, but not all, known fronto-facial ‘kindchenschema’ features, and this may well contribute to their apparently cute appearance and to their current popularity as companion animals. We conclude that the challenge of addressing conformation-related disorders in companion dogs needs to take account of the cute, ‘kindchenschema’ looks that many owners are likely to be attracted to.
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We aimed to clarify the changes in facial morphology of cats in relation to their interactions with humans. In Study 1, we compared the facial morphology of cats (feral mixed breed, owned domestic mixed breed, and owned domestic purebreds) with that of African wildcats. After collecting 3295 photos, we found that owned domestic cats’ noses were significantly shorter than those of African wildcats and feral mixed breed, and there were no significant differences between the latter two. The eye angles were significantly more gradual in owned domestic purebreds than in the other groups. In Study 2, we examined the correlation between facial morphology and years with the owner, and found that the former is not affected by the latter. This suggests that changes in facial morphology are possibly transgenerational changes. The difference in facial morphology between wildcats and owned cats might be caused by domestication, and that between feral cats and owned cats might be due to feralization. In Study 3, we investigated whether cats’ facial features affect cuteness ratings. We asked human participants to evaluate the cuteness of cats’ face images and found that faces with shorter nose lengths were considered cuter. This suggests that owned domestic cats’ facial morphology is preferred by humans.
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Advances in animal motion tracking and pose recognition have been a game changer in the study of animal behavior. Recently, an increasing number of works go ‘deeper’ than tracking, and address automated recognition of animals’ internal states such as emotions and pain with the aim of improving animal welfare, making this a timely moment for a systematization of the field. This paper provides a comprehensive survey of computer vision-based research on recognition of pain and emotional states in animals, addressing both facial and bodily behavior analysis. We summarize the efforts that have been presented so far within this topic—classifying them across different dimensions, highlight challenges and research gaps, and provide best practice recommendations for advancing the field, and some future directions for research.
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Comparing homologous expressions between species can shed light on the phylogenetic and functional changes that have taken place during evolution. To assess homology across species we must approach primate facial expressions in an anatomical, systematic, and standardized way. The Facial Action Coding System (FACS), a widely used muscle-based tool for analyzing human facial expressions, has recently been adapted for chimpanzees (Pan troglodytes: ChimpFACS), rhesus macaques (Macaca mulatta: MaqFACS), and gibbons (GibbonFACS). Here, we present OrangFACS, a FACS adapted for orangutans (Pongo spp.). Orangutans are the most arboreal and the least social great ape, so their visual communication has been assumed to be less important than vocal communication and is little studied. We scrutinized the facial anatomy of orangutans and coded videos of spontaneous orangutan behavior to identify independent movements: Action Units (AUs) and Action Descriptors (ADs). We then compared these facial movements with movements of homologous muscles in humans, chimpanzees, macaques, and gibbons. We also noted differences related to sexual dimorphism and developmental stages in orangutan facial morphology. Our results show 17 AUs and 7 ADs in orangutans, indicating an overall facial mobility similar to that found in chimpanzees, macaques, and gibbons but smaller than that found in humans. This facial movement capacity in orangutans may be the result of several, nonmutually exclusive explanations, including the need for facial communication in specialized contexts, phylogenetic inertia, and allometric effects.
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In the past, dogs were bred to perform specific utilitarian roles. Nowadays, the dog's most common role is that of human companion. Our world has changed dramatically since the first dog breeds were developed, yet many of these existing breeds remain popular as companions. While dogs kept as companions can provide a range of benefits to humans, in some cases the relationship between dog and human can be tenuous or even dangerous. Many dogs exhibit behaviours their owners consider undesirable and these dogs may cause disruption and injury to humans and other animals. As a consequence, many are relinquished to shelters. It is proposed that some of this unsuitable behaviour may be the result of inappropriate dog-owner matching, made more likely by the general change in the role of dogs, from working dog to companion animal, coupled with a strong tendency for modern owners and breeders to select dogs primarily on the basis of morphological, rather than behavioural, characteristics. This paper highlights how roles for dogs have changed and the importance of taking physical health and behaviour, as well as perceived beauty, into consideration when breeding and selecting dogs as companions. The measurement of behaviour and limitations of existing canine behaviour assessments are discussed. Finally, it is suggested that scientific development of accurate behavioural assessments, able to identify desirable canine behavioural traits, would provide invaluable tools for a range of dog-related organisations.
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The origin of domestic dogs remains controversial, with genetic data indicating a separation between modern dogs and wolves in the Late Pleistocene. However, only a few dog-like fossils are found prior to the Last Glacial Maximum, and it is widely accepted that the dog domestication predates the beginning of agriculture about 10,000 years ago. In order to evaluate the genetic relationship of one of the oldest dogs, we have isolated ancient DNA from the recently described putative 33,000-year old Pleistocene dog from Altai and analysed 413 nucleotides of the mitochondrial control region. Our analyses reveal that the unique haplotype of the Altai dog is more closely related to modern dogs and prehistoric New World canids than it is to contemporary wolves. Further genetic analyses of ancient canids may reveal a more exact date and centre of domestication.
Physical traits that are characteristic of human infants are referred to as baby‐schema, and the notion that these affect perception of cuteness and elicit care giving from adults has a long history. In this study, infant‐similarity was experimentally manipulated using the difference between adult and infant faces. Human infant, human adult and cat faces were manipulated to look more (human) infant‐like or adult‐like. The results from the current study demonstrate the impact of infant‐similarity on human adults' perception of cuteness across the three different types of face. The type of face had a large impact on perceived cuteness in line with the expected infant‐similarity of the images. Infants and cats were cutest while adults were less cute. The manipulations of infant‐similarity, however, had similar effects on the perception of cuteness across all three types of face. Faces manipulated to have infant‐like traits were rated as cuter than their equivalents manipulated to have adult‐like traits. These data demonstrate that baby‐like traits have a powerful hold over human perceptions and that these effects are not simply limited to infant faces.
Hinde & Barden (1985, Anim. Behav., 33, 1371–1373) suggested that the teddy bear has evolved to match sign stimuli that release nurturant behaviour. Bears are usually bought for infants and young children. From an evolutionary perspective it seems paradoxical that young children who themselves require intensive nurture should exhibit a preference for objects that afford nurturing. The purpose of this study was to investigate the origin of the preference for nurturant sign stimuli. The preference for baby-featured bears was examined in three age groups: 4, 6 and 8 year olds. The 6 and 8 year olds significantly preferred baby-featured bears: however, the 4 year olds did not. The evolution of the teddy bear is thus apparently not driven by the ostensible consumer, the young child; the preference for baby features may be part of a wider, relatively late development of nurturant feelings towards young.