A Multispecies Approach to Co-Sleeping: Integrating Human-Animal Co-Sleeping Practices into Our Understanding of Human Sleep

Abstract

Human sleeping arrangements have evolved over time and differ across cultures. The majority of adults share their bed at one time or another with a partner or child, and many also sleep with pets. In fact, around half of dog and cat owners report sharing a bed or bedroom with their pet(s). However, interspecies co-sleeping has been trivialized in the literature relative to interpersonal or human-human co-sleeping, receiving little attention from an interdisciplinary psychological perspective. In this paper, we provide a historical outline of the “civilizing process” that has led to current sociocultural conceptions of sleep as an individual, private function crucial for the functioning of society and the health of individuals. We identify similar historical processes at work in the formation of contemporary constructions of socially normative sleeping arrangements for humans and animals. Importantly, since previous examinations of co-sleeping practices have anthropocentrically framed this topic, the result is an incomplete understanding of co-sleeping practices. By using dogs as an exemplar of human-animal co-sleeping, and comparing human-canine sleeping with adult-child co-sleeping, we determine that both forms of co-sleeping share common factors for establishment and maintenance, and often result in similar benefits and drawbacks. We propose that human-animal and adult-child co-sleeping should be approached as legitimate and socially relevant forms of co-sleeping, and we recommend that co-sleeping be approached broadly as a social practice involving relations with humans and other animals. Because our proposition is speculative and derived from canine-centric data, we recommend ongoing theoretical refinement grounded in empirical research addressing co-sleeping between humans and multiple animal species.

Full text

A Multispecies Approach to Co-Sleeping
Integrating Human-Animal Co-Sleeping Practices into Our
Understanding of Human Sleep
Bradley P. Smith
1
&Peta C. Hazelton
1
&Kirrilly R. Thompson
1
&
Joshua L. Trigg
1
&Hayley C. Etherton
1
&Sarah L. Blunden
1
#Springer Science+Business Media New York 2017
Abstract Human sleeping arrangements have evolved over time and differ across
cultures. The majority of adults share their bed at one time or another with a partner
or child, and many also sleep with pets. In fact, around half of dog and cat owners
report sharing a bed or bedroom with their pet(s). However, interspecies co-sleeping
has been trivialized in the literature relative to interpersonal or human-human co-
sleeping, receiving little attention from an interdisciplinary psychological perspective.
In this paper, we provide a historical outline of the “civilizing process”that has led to
current sociocultural conceptions of sleep as an individual, private function crucial for
the functioning of society and the health of individuals. We identify similar historical
processes at work in the formation of contemporary constructions of socially normative
sleeping arrangements for humans and animals. Importantly, since previous examina-
tions of co-sleeping practices have anthropocentrically framed this topic, the result is an
incomplete understanding of co-sleeping practices. By using dogs as an exemplar of
human-animal co-sleeping, and comparing human-canine sleeping with adult-child co-
sleeping, we determine that both forms of co-sleeping share common factors for
establishment and maintenance, and often result in similar benefits and drawbacks.
We propose that human-animal and adult-child co-sleeping should be approached as
legitimate and socially relevant forms of co-sleeping, and we recommend that co-
sleeping be approached broadly as a social practice involving relations with humans
and other animals. Because our proposition is speculative and derived from canine-
centric data, we recommend ongoing theoretical refinement grounded in empirical
research addressing co-sleeping between humans and multiple animal species.
Hum Nat
DOI 10.1007/s12110-017-9290-2
*Bradley P. Smith
b.p.smith@cqu.edu.au
1
Appleton Institute, Central Queensland University, 44 Greenhill Road, Wayville,
SA 5034, Australia

Keywords Co-sleeping .Human-animal co-sleeping .Human-animal relationship .
Social norms .Pets .Dogs
The relationship between humans and other animals has a long history. Since the
domestication and socialization of animals in the late Pleistocene (~12,000 years BP),
animals have been recognized across various cultures for their ability to aid human
survival, health, and healing (Thompson and Smith 2014; Walsh 2009). Domestic dogs
(Canis familiaris), in particular, have lived alongside humans for at least this long and
are considered one of the most successfully adapted human-domesticated animals
(Clutton-Brock 1999;Frantzetal.2016;Larsonetal.2012; Vilà et al. 1997).
Present-day Western and modern industrialized societies show consistently high levels
of pet ownership. In Australia, for example, almost two thirds of households contain a
pet (Australian Companion Animal Council 2010). Strong psychological attachment to
pets is also common (Archer 1997) and for some, the relationship with their pet may
supplement or even supplant interpersonal relationships (Veevers 1985). Recently,
investigations into the sleeping behavior of pet owners has revealed that pets play as
significant a role in the sleeping lives of their owners as they do in their waking lives
(Smith et al. 2014; Thompson and Smith 2014). Allowing animals to live inside the
home, as well as to share the private space of the bed and/or bedroom, highlights the
value and status that is bestowed on them. Around half of pet owners (predominantly of
dogs and cats) share their bedroom or bed with their pet(s) during the night (Shepard
2002; Smith et al. 2014;ThompsonandSmith2014). Although human-animal co-
sleeping is not a new phenomenon, what we know about the practice of co-sleeping is
limited to studies of human adults, or parent-child co-sleeping arrangements. This has
led to an incomplete and anthropocentric understanding of co-sleeping.
In this review, we discuss interpersonal and interspecies co-sleeping in parallel, with
a focus on humans sleeping with dogs. Given the similarities between adult-infant and
human-dog sleeping, we propose that human-animal co-sleeping deserves greater
academic consideration. By approaching co-sleeping broadly as a social practice
involving human relations with other human and non-human animals, we respond to
a call for a greater understanding of the variable manifestations and meanings of sleep
(Williams et al. 2010). Moreover, a comprehensive understanding of human-animal co-
sleeping has significant practical implications for human sleep, human-animal relations,
and animal welfare.
Background
Defining Co-Sleeping
Definitions of “co-sleeping”or “bed sharing”usually infer human partners sharing a
bed, or parents and children sharing a bed or bedroom (Ball 2006; Dittami et al. 2007;
Goldberg and Keller 2007; McKenna and Volpe 2007). Goldberg and Keller define
parent-infant co-sleeping as when both are “in close enough proximity to exchange at
least two sensory stimuli, such as touch, smell, movement, sight and/or sound”
(2007:459). Moreover, co-sleeping need not occur for the entire night, but rather, any
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portion of the night (Ball 2002). Although definitions vary, they fail routinely to include
non-human animals. In this review, we advocate an extension of the definition of
human co-sleeping to include sharing beds or rooms with animals.
The Evolution of Co-Sleeping
The sleeping body is considerably vulnerable (Hislop 2007; Williams and Crossley
2008). As a result, individuals may only allow people into their home or bed whom
they trust (Ekirch 2001; Williams and Crossley 2008; Worthman and Melby 2002).
With the exception of beliefs around out-of-body and numinous experiences (McCaul
2008), the sleeping body is typically thought of as non-relational and involuntary.
However, co-sleeping arrangements require negotiation between dysfunctions or con-
flicts and the perceived social and psychological benefits (Meadows 2005; Williams
et al. 2010). From this perspective, sleep can be approached as the interaction of
individual biological requirements and shared social experience (Meadows et al.
2008). Co-sleeping, however, extends beyond interpersonal relationships, with the
addition of non-human animals into human sleep practices. This has the potential to
provide valuable insight about human co-sleeping practices, the social dimensions of
sleep, and interspecies relations.
Sleeping arrangements have evolved over time and across cultures. In medieval
European society—spanning the fifth to fifteenth centuries—for instance, sleep was a
public and communal affair in which it was not uncommon to receive visitors in the
bedroom, or for many people to sleep in the same bed (Arber et al. 2012). During this
period, it was also customary to share a bed with passing travelers and for students
attending boarding schools to share beds (Crook 2008). Sleeping with others was viewed
by some as a way to increase personal security (Worthman and Brown 2007), conserve
resources, and generate warmth (Ekirch 2001). By the fifteenth to seventeenth centuries in
the British Isles, household beds became increasingly important, and represented signif-
icant assets that were reserved for those with the means to afford them. Parents most likely
slept apart from children other than infants, although occasionally, entire households of
European peasants shared the same beds (Ekirch 2001,2006).
In contemporary Western or industrialized cultures, however, sleep is commonly
regarded as an individual and private experience in which the body and mind are able to
optimally rest and recuperate (Williams et al. 2010). This normative shift from sleep as
a public and social affair to a private one arose through a complex “civilizing”process
(Elias 1929). During the Victorian era (1837–1901), a domestic ideology emerged
which questioned the established practice of a single bedroom sheltering multiple
sleeping bodies, often from different families. In some circumstances, limitations on
available bedchambers forced all family members to share a single bed (Crook 2008).
This raised concerns about interfamily promiscuity and the even greater “moral evil”of
incest (Crook 2008). Given this context, social norms and rules began to dictate that
each person should sleep in a single bed, in a private place away from public view, and
wearing appropriate sleeping attire, gradually introducing the concept of the private
bedroom and private sleep to many social classes (Arber et al. 2012).
The emergence of the individual sleeping space was increasingly viewed as an
indicator of wealth and prosperity in many Western industrialized societies, and private
sleeping arrangements became sought after as a symbol of prestige (Blunden et al.
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2011;Crook2008;Ekirch2001). Modern medical and scientific understanding further
normalized private sleep spaces by identifying aspects of parent-child co-sleeping as
risk factors for Sudden Infant Death Syndrome (SIDS), and by advocating that infants
sleep in a separate space in the parents’bedroom (Moon 2011). Parents choosing to
ignore this perspective and continue co-sleeping are sometimes viewed as negligent,
rebellious, or selfish, which can produce feelings of embarrassment, shame, or stigma
(Arber et al. 2012).
By privatizing sleep, the “civilizing”process introduced four general functions of sleep
and the bedroom: (1) Independence, where privacy, autonomy, and personal control
became normative dimensions of adult sleep (Arber et al. 2012); (2) Health,wherethe
bedroom became a place for convalescence when injured or unwell (Crook 2008); (3)
Functionality, where sleep has become more positively construed as fundamental for
enhanced productivity and performance in everyday life; and (4) Sexual relations,where
the increased number of bedrooms within a household enabled greater sexual segregation
between children and their parents (Crook 2008). These four beneficial functions of sleep
and the bedroom have been well researched in relation to interpersonal co-sleeping
practices, with a focus on adult-adult and parent-child co-sleeping practices.
Adult-Adult Co-Sleeping
Decisions regarding sleeping partners vary greatly not only between cultures, but also
within different social and cultural groups (Williams and Crossley 2008; Williams et al.
2010; Worthman and Brown 2007). For example, among the semi-nomadic Efé people,
located in the Ituri rainforest of the Democratic Republic of Congo, virtually no
individual sleeps alone (see Worthman and Melby 2002). It would not be uncommon
for grandparents, two adults, and visitors to sleep together. Williams et al. (2010)note
that the vast majority of adults in modern society do not sleep alone, particularly those
in Western postindustrial populations. Moreover, choice of bed companions can mirror
and strengthen social relationships and structure, and research has found that member-
ship within a social unit partly determines with whom people choose to sleep
(Worthman and Brown 2007).
Conversely, sleeping partners may generate conflict over different sleep require-
ments, differences in body temperature, as well as sleep behaviors such as snoring,
restless legs, sleep-talking, and parasomnias (Hislop 2007;Meadows2005). Despite
these inconveniences, couples continue to co-sleep for reasons linked to social and
physical intimacy, reassurance, companionship, mutual trust, vulnerability, and a culture
of togetherness, particularly in contemporary Western societies (Hislop 2007; Williams
et al. 2010). In one case presented by Meadows (2005), a male participant continued to
sleep with his partner despite frequently disturbing her throughout the night or when she
was ill. The participant argued that the intimate nature of co-sleeping was far more
valuable than sleep quality. Meadows (2005) argues that although the closeness of
sleeping together is a social product, psychological factors also impact adult co-sleeping.
Parent-Child Co-Sleeping
In Western cultures, parent-child co-sleeping is a highly contentious practice among
parents and experts, fraught with confounding factors and definitional issues (Goldberg
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and Keller 2007; McKenna and Volpe 2007; McKenna et al. 2007), health concerns,
and taboo. Leading health and pediatric organizations advise against parents and
children sharing a bed because of a positive correlation with Sudden Infant Death
Syndrome (SIDS). Yet other experts in pediatric sleep, medicine, and breastfeeding
strongly question these recommendations because of their impact on parenting beliefs,
cultural values, and breastfeeding duration (Blunden et al. 2011; McKenna et al. 2007).
They further argue that there are ways to mitigate bed-sharing risks, such as using
appropriate bedding or having the child’s and parents’beds in the same room
(McKenna and McDade 2005; McKenna et al. 2007). Despite these opposing views,
sleeping with children from birth remains the norm in many cultures, as has been
observed in rural and urban Egypt (Worthman and Brown 2007) and indigenous
cultures in unindustrialized populations (Blunden et al. 2011). Intergenerational co-
sleeping is generally more prevalent in collectivist Asian countries (Mindell et al. 2010)
than in the more individualistic West (Ramos et al. 2007).
Human-Animal Co-Sleeping
Whilst co-sleeping practices of adult-adult and parent-child arrangements have been
well researched (as previously outlined), sleeping or sharing a bed with animals has
been relatively ignored. Yet sleeping with, or alongside, animals is not novel. Early
anthropological accounts of “traditional”cultures that mention co-sleeping with ani-
mals tend to emphasize the benefits of human-animal co-sleeping. In particular, dogs
seem to serve a protective purpose. Aboriginal Australians, for instance, were often
reported to sleep alongside their dogs (and/or dingoes) for warmth and for protection
from evil spirits (Smith and Litchfield 2009). Indeed, the reference to a “three dog
night”—a night so cold, it takes sleeping with three dogs to keep warm—has since
become an Australian colloquialism (Smith and Litchfield 2009;ThompsonandSmith
2014). Gabra herders in northern Kenya have also been observed to sleep in close
proximity to their watchdogs tasked with driving off predators and alerting them to
stock raiders (Worthman and Melby 2002). In preindustrial England, dogs were placed
outside the sleeping quarters to guard the occupants and alleviate security-related
anxieties (Ekirch 2001). During this time cats were often given free range within the
sleeping quarters to help keep pests, such as rodents, at bay (Ekirch 2001). It was also
not uncommon for families throughout the British Isles to bring farm animals into their
sleeping quarters. This allowed for the protection of cows, sheep, and other livestock
from predators and thieves and also provided additional warmth (Ekirch 2001,2006).
In a cross-cultural study of human-pet dynamics across 60 (non-Western) societies,
Gray and Young (2011) found that pet ownership practices, and the species kept,
differed. This was evident in feeding practices, positive interactions with pets (e.g.,
grooming, playing), negative interactions with pets (e.g., killed to be eaten, physical
abuse), and in the sleeping location of these animals: outside, inside, away from people,
or near people). Dogs, the most commonly kept pets in 53 of the 60 societies, and cats,
were about as equally likely to be reported sleeping outside, inside away from people,
or inside near people. Of the 53 societies in which dogs were kept as pets, seven
allowed them indoors. In only six of the societies did dogs have “nocturnal sleeping
arrangements”both within the home and near people. Cats were permitted indoors at
night around people in only two cultures. The findings from this cross-cultural study
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suggest that co-sleeping with animals was historically uncommon. This research also
proposed that the doting on pets apparent in modern Western cultures—including co-
sleeping practices—is a cross-cultural aberration, albeit one that has spread widely in
recent decades (Gray and Young 2011). Although pet ownership in contemporary
industrialized countries is quite common, the prevalence and reasons for the practice
of human-animal co-sleeping are not well understood. As with parent-infant co-
sleeping, pet owners appear divided in their decision to co-sleep. Various cross-
sectional research conducted by media groups, the pet care and pet food industries,
and predominantly from non-dedicated or non-validated surveys, suggests that approx-
imately one in two pet owners share their beds or bedroom with their pets (Duthuluru
et al. 2014; Shepard 2002;ThompsonandSmith2014).
Whilst little to nothing has been written about the impact of the “civilizing”process
on human-animal co-sleeping, the same four general functions of sleep and the
bedroom described above can also be observed in social proscriptions or taboos around
human-animal co-sleeping. That is, sleeping independently from animals could be seen
as a part of this “civilizing”process that: (1) distinguishes human behavior from more
“animal-like”behaviors; (2) reduces the risk of contracting zoonotic diseases—recall
the phrase, “If you lie down with dogs, you get up with fleas”; (3) enables the higher-
quality sleep required to effectively contribute to society during waking hours; and (4)
avoids inappropriate sexual contact with animals (see point 1). Overall, these functions
discouraging human-animal co-sleeping can be related to the enforcement of a demar-
cation between human culture and animal nature (Ortner 1974). However, the need
for—and implications of—prioritizing human culture over animal nature are being
increasingly challenged, as evidenced in environmental movements, animal-welfare-
and rights-based social action, psychological investigations into humans’“creatureli-
ness”(Beatson and Halloran 2007), and sustained research interest regarding potential
benefits of human-animal relations.
Disincentives for Human-Animal Co-Sleeping
Current perspectives view both human-animal co-sleeping and interpersonal co-
sleeping (e.g., parent-child) with the same apprehensions and tend to focus on the
negative aspects or consequences of human animal co-sleeping (e.g., Smith et al. 2014;
Thompson and Smith 2014). The following section explores these concerns. The
parallels between child and animal co-sleeping behavior can be grouped into four
overarching concerns: (1) health, (2) impaired functioning, (3) avoiding the develop-
ment of problematic behaviors, and (4) sexual dysfunction.
Health Concerns
Co-sleeping with infants remains a controversial topic primarily because of its links
with infant injury and mortality since bed sharing is an identified risk factor associated
with SIDS. In addition, bed-sharing infants are more prone to sleep accidents, including
being crushed by a parent, resulting in entrapment and suffocation. This finding is still
debated as other factors, such as parental smoking, drug and alcohol use, bedding used,
and overcrowding, are greater risk factors and confound some reported results
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(Goldberg and Keller 2007; McKenna and McDade 2005; McKenna et al. 2007). As a
result, several major health and parent organizations, including the American Academy
of Pediatrics, strongly discourage bed sharing because of this potential risk, resulting in
many Western parents now avoiding the practice. However, co-sleeping is often
referred to only as bed sharing (Thoman 2006) whereas co-sleeping actually also
includes room sharing, creating confusion for parents and a fear and avoidance of co-
sleeping more broadly. A number of parent and health organizations advocate for room
sharing in the first 6–12 months of life, as this has been found to reduce the risk of SIDS
(McKenna and McDade 2005; McKenna et al. 2007). Consequently, discourse regard-
ing parent-child co-sleeping remains convoluted, contradictory, and confusing, with the
result that some parents generally avoid co-sleeping. Parents who choose to co-sleep
may be viewed by some people as neglectful of their child’ssafety(Arberetal.2012).
Although SIDS is not an explicit concern when considering human-animal co-
sleeping, the practice of co-sleeping with animals can be perceived as controversial
for other issues, such as those relating to the transmission of zoonotic diseases.
Zoonoses are a product of interaction between humans and domestic or wild animals,
and exposure to certain diseases can be exacerbated by human-animal co-sleeping
(Beck 1975;Love2010). A series of recommendations aimed at preventing the spread
of disease associated with animals from various North American veterinarian and
public health organizations, concluded that sharing a bed with a dog was significantly
associated with infections such as Chagas disease, Methicillin-resistant Stapylococcus
aureus infections, Capnocytophaga canimorsus,andPasteurella spp. (Chomel and Sun
2011). However, zoonotic infections acquired from sleeping with a pet are relatively
uncommon (Chomel and Sun 2011;Herzog2014), particularly if the animal is kept
clean and receives regular veterinary attention (Smith 2012). Also, the aforementioned
recommendations were based on very rare cases (Chomel and Sun 2011;Herzog2014).
On the other hand, whilst the focus of contracting zoonotic diseases primarily targets
their transmission from animals to humans, two thirds of human diseases are zoonotic
and can also infect animals (Cleaveland et al. 2001). Therefore, co-sleeping can impact
not only the owner’s health, but also the health of the pet. Apart from contracting
zoonotic diseases, co-sleeping with pets is known to provoke allergies or asthma in
some pet owners as allergens are commonly shed on animal fur, contributing to the
view that having a dog in the bed is unhygienic (Plaut et al. 1996).
Impaired Functioning
Co-sleeping increases individual vulnerability to nightly disturbances that may impair
daily functioning. In adult-adult co-sleeping, women are more likely than men to
experience disturbances throughout the night (Dittami et al. 2007). Bed partners of
individuals who experience sleep disorders, such as obstructive sleep apnea, frequently
awaken throughout the night, resulting in decreased sleep efficiency (Beninati et al.
1999; Troxel et al. 2009). Research also suggests that children who co-sleep with
parents have more nighttime awakenings, which may in turn impact the parents’
functioning the next day (Keller and Goldberg 2004). Chronic and severe sleep
disruption can leave parents vulnerable to depression, impaired physical health, in-
creased stress, and reduced overall quality of life (Sadeh et al. 2011; Richard et al.
1998). Children may also suffer the consequences of ongoing disrupted sleep, including
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compromised maturation, affect regulation, memory consolidation, and learning, as
well as impacts on cognitive functioning and behavior regulation (Sadeh 2007).
Severe sleep disturbance resulting from sharing a bed has the potential to impair
daytime functioning and well-being. However, less severe disturbances consisting of
fewer awakenings or shorter disruptions (see Keller and Goldberg 2004) may not be
enough to cause significant daytime impairment. This suggests that the number of
wakings itself is unlikely to be a suitable indicator of impaired daytime functioning
specifically associated with co-sleeping. Finally, it is likely that co-sleeping parents are
more aware of their children’s nighttime disturbances because they are in closer
proximity to their child throughout the night (Ramos et al. 2007). This also suggests
that nighttime awakenings might be underreported for non-co-sleeping infants.
However, not all awakenings are negative. For example, McKenna and Gettler
(2016) describe the practice of “breastsleeping”and argue that awakenings while co-
sleeping are actually healthy and normal for breast-feeding. Further, differences may
exist between human-human and human-pet attachment relating to ongoing physiolog-
ical regulation (for example, physiological regulatory effects such as heart rate, breath-
ing rate, body temperature, blood pressure) that underlies sleep disturbances or frag-
mentation. Thus, disturbances can be viewed as a means of resetting or correcting heart
perturbations, aiding in oxygenation, and partner-induced arousals can lead to healthier
infant sleep, sensory-based—transient and epochal—arousals and engagements. Since
solitary sleep in sensory-deprived environments pushes infants into deeper sleep stages,
it can decrease the likelihood of infants arousing to terminate apneic episodes and
reinitiate breathing (see McKenna and McDade 2005). It would clearly be worthwhile
to improve our understanding of these mutual regulatory processes between adults and
pets, in comparison with adults and adults, and adults and infants.
Undoubtedly, the presence of an animal in the bed or bedroom may negatively
impact sleep quality and quantity. One point of difference, however, is that although co-
sleeping with children may create sleep disturbances that impair daily functioning of
both parent and infant, human-animal co-sleeping disruptions are most likely to affect
only the functioning of the pet owners (Smith et al. 2014). In a survey of Australian
sleeping practices, Smith et al. (2014) compared owners who co-slept with their pets
(10%) with those choosing not to. In age- and gender-matched comparisons,
disregarding ownership status and pet species, results suggested that co-sleeping with
pets negatively impacted sleep latency and quality. Consequently, owners sharing a bed
with their pet took longer to get to sleep, were more likely to feel tired upon waking,
and were more likely to report sleep disturbances from animal noises throughout the
night than were those who did not share their bed with their pet. Yet, these findings
regarding the link between co-sleeping and sleep quality were limited in scope, as data
did not reveal the location of the pet in room, the species of pet, the exact impact of a
pet on sleep latency, the sources of animal noises disrupting sleep, or whether distur-
bances were considered problematic by owners (Smith et al. 2014).
In an American study of pet-owner co-sleeping by Duthuluru et al. (2014)similar
findings were reported: almost a third of pet owners who co-slept (n= 148) reported
being awakened by the pet at least once per night, and those who co-slept more than
four nights per week also reported poorer sleep quality. These figures are comparable to
those in studies of parent-infant co-sleeping (Goldberg and Keller 2007). Sleep distur-
bances arising from human-animal co-sleeping may also be related to mismatched sleep
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cycles (Campbell and Tobler 1984). In particular, dogs sleep polyphasically, averaging
three sleep/wake episodes per nighttime hour, with active sleep immediately preceding
spontaneous arousals that may conflict with the monophasic sleep/wake cycles of
humans (Adams and Johnson 1994; Smith et al. 2014). Furthermore, Adams and
Johnson (1994) found that regardless of a dog’s sleeping state, whether they are in
active or quiet sleep, they remain responsive to auditory stimuli, particularly barking.
Unfortunately, without objectively measuring sleep quality in these co-sleeping ar-
rangements—such as through simultaneous actigraphic and accelerometric measure-
ment of pet and owner sleep—determining the physiological impact of such sleep
disruptions is problematic.
Problematic Behaviors
Parent-child co-sleeping has been reported to produce undesirable behaviors in children,
including bedtime resistance (Lozoff et al. 1984; Mandansky and Edelbrock 1990)and
dependency (Brazelton 1992;Ferber1985). Since the privatization of sleep in Victorian
times, co-sleeping has been viewed by some as an indulgence that “spoils”and may lead
to “lazy”and recalcitrant children (Jenni and O’Connor 2005). Co-sleeping children
may exhibit abnormal psychological dependency and display separation anxiety when
separated from their parents during the day (Morelli et al. 1992). Parents have reported
that parent-child co-sleeping is related to sleep problems that promote maladaptive
sleep-onset associations and habits that are reliant on parent interaction (Mandansky
and Edelbrock 1990; Mao et al. 2004; Mindell et al. 2010; Ramos et al. 2007). When
mothers provide continuous bodily contact throughout waking and co-sleeping periods
to reduce anxiety and tension, infants may begin to depend on their presence for
emotional regulation and be more likely to experience profound distress when separated
from the parent, both during the day and at night (Sadeh et al. 2010).
Importantly, arguments proposing that co-sleeping leads to negative effects are
neither straightforward nor conclusive, particularly for human-infant dyads. Many
studies detailing negative behavioral outcomes resulting from co-sleeping largely
depend on whether the co-sleeping is a deliberate choice of the mother or is a reaction
to another’sbehavior(“reactive co-sleeping”; e.g., Mandansky and Edelbrock 1990).
The particular culture being studied should also be used to frame interpretations; co-
sleeping is frequently discussed from the perspective of a Western, industrialized society
(e.g., Mao et al. 2004), which does not necessarily reflect normative behavior worldwide
(see McKenna et al. 2007). Indeed, several studies have reported positive outcomes from
co-sleeping that may relate to both human-human and interspecies co-sleeping. For
example, Keller and Goldberg (2004) note that children who sleep with their parents
while young are in fact are more self-reliant and exhibit more social independence,
rather than the opposite. Heron (1994) also reported that children who were never
permitted to share their beds were more fearful and more difficult to control than
children who consistently slept in their parents’bed at night. Mosenkis (1998)found
far more positive than negative adult outcomes for individuals who co-slept as a child,
among multiple ethnic groups: African Americans and Puerto Ricans in New York and
Puerto Ricans, Dominicans, and Mexicans in Chicago. Across all of these groups, co-
sleepers exhibited greater feelings of satisfaction with life than did non-co-sleepers. The
benefits may also extend to the mothers themselves; women who co-slept as children
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had higher self-esteem than those who did not (Crawford 1994). Thus, co-sleeping,
contrary to some opinion, may indeed promote confidence, self-esteem, and intimacy,
possibly by reflecting an attitude of parental acceptance (Lewis and Janda 1988).
As with parent-infant co-sleeping, co-sleeping with animals may produce similar
undesirable or dysfunctional behaviors in the pets as it does in infants. Dog owners are
often advised that letting a dog sleep on the bed may “spoil”the dog and cause
undesirable behaviors (Voith et al. 1992). Multiple sources suggest that allowing dogs
into the bedroom may create competitive aggression, predominantly when attention is
not paid to the dog, or the dog may become aggressive toward other dogs in the
household (see Thompson and Smith 2014). For example, competitive aggression and
separation-related elimination problems—such as urination and defecation—may be
more prevalent among room-sharing dogs (Jagoe and Serpell 1996) and, conceivably,
dog-owner co-sleeping might produce an “unbalanced”attachment, favoring a stronger
attachment of the dog to the human, exacerbating adverse reactions to separation (Jagoe
and Serpell 1996). Conversely, and as mentioned earlier, pets may be invited into the
bedroom as a result of behavioral problems, such as scratching at doors or repetitive
barking if excluded from the room (Thompson and Smith 2014). That implies that
negative outcomes may exist independent of the co-sleeping arrangement, and that co-
sleeping amplifies or perpetuates these issues within both children and pets. At present,
it is difficult to determine directionality: whether behavioral problems are antecedents
or consequents of co-sleeping arrangements.
Sexual Dysfunction
Parent-child co-sleeping may raise concerns involving sexuality in the bedroom,
particularly as children get older. When the “civilizing”process increased segregation
between children and their parents, it established and enforced “controlled”and
“acceptable”infant-parent relationships (Blunden et al. 2011; Crook 2008). Co-
sleeping can increase children’s proximity to auditory and visual exposure to adult
sexual behavior and, as a result, has been labeled as one potential indicator of
emotionally incestuous parenting, which may represent a perversion of childhood
(Okami 1995;Thompson2010). Some literature has even suggested that co-sleeping
may promote abnormal attraction to the maternal caregiver, or convey messages of
seduction to children who imitate adult sexualized behavior without adequately under-
standing the context (Okami 1995;Thompson2010). Furthermore, co-sleeping can
interfere with physical intimacy and sexual relationships between parents because of
the child’s close proximity. Having this third person in the adult caregivers’bed creates
a distraction and a competitor for the concern, attention, and affection of one or both
sexual partners (Stein et al. 1997). Parents who co-sleep with older children (5–9years)
report significantly higher level of marital distress than parents of solitary sleepers
(Cortesi et al. 2008), which may be related to this reduced opportunity for intimacy.
Whilst this may be true, the argument for sexual dysfunction as a result of co-sleeping
is somewhat tenuous. Germo et al. (2007) found no difference in overall adult relation-
ship satisfaction between solitary sleeping, early co-sleeping, and reactive co-sleeping
parents living with younger children. In a study of extended parental absence during
employment rotation—with one partner in the military—children who co-slept, includ-
ing older boys (≥3 years) who shared a bed with their mothers, exhibited few emotional
Hum Nat

or behavioral problems and were even underrepresented in corresponding base psychi-
atric populations (Forbes et al. 1992). A longitudinal examination of bed-sharing effects
on life cycle stages from infancy to 18 years of age concluded that sharing a bed in
infancy and early childhood displayed no association with sleep problems, sexual
pathologies, or any other problematic consequences (Okami et al. 2002). The authors
concluded that when bed sharing is practiced safely, and as a part of valued family
relational dynamics, the likelihood of harm was minimal (Okami et al. 2002).
Animals’presence in the bed or bedroom may interrupt normative sexual relations
between bed partners, which could then act as a source of conflicts or issues regarding
intimacy between couples, particularly if the pet is unwelcomed in the bed by one
partner only (Thompson and Smith 2014). Co-sleeping alongside animals may also
raise concerns of sexual acts involving pets (Miletski 2005). Although this practice has
been evident throughout human history, its affiliation with unhealthy romantic attach-
ments, socially aberrant sexual acts, and particularly its animal welfare implications
support its illegality and low prevalence (Dekkers and Vincent 1994;Miletski2005).
There is, however, little reason to link zoophilia among pet owners as a prevalent and
normative motivation for co-sleeping.
Motivations for Human-Animal Co-Sleeping
Despite the many apprehensions surrounding human-animal co-sleeping, its high inci-
dence would suggest that its advantages likely outweigh any disadvantages. Despite
potential negative repercussions of human-animal co-sleeping, approximately half of all
animal owners appear to remain motivated to co-sleep with their pets, suggesting that
there are likely benefits to continuing the practice. Clearly, co-sleeping with a pet
considerably increases the time an owner spends proximate to the animal. Given that
some studies have reported that pet ownership can provide a number of benefits to human
physical, psychological, and social health (Crawford et al. 2006;Smith2012), this
suggests that co-sleeping may provide or enhance psychological benefits. Yet the opposite
may hold true for some owners. For example, those who are lonely may be more likely to
sleep with their pets, and whilst this may be comforting, an unhealthy pathological level of
pathological attachment may ensue (see “Attachment and Emotional Closeness”).
Our understanding of what motivates humans to share their bed with their pets is
currently limited. However, motivations for parents choosing to co-sleep with children
appear to be relatively well-established (Ball 2002). As in parent-infant co-sleeping, the
decisions made by a pet owner about where their pet sleeps during the night are
dependent upon philosophical, psychological, and cultural orientations, as well as
emotional and practical factors (Smith et al. 2014). Given that there is likely to be some
similarity with parent-child co-sleeping, the following section considers how motiva-
tions explaining adult-child co-sleeping may extend to human-animal co-sleeping.
Early Co-Sleepers and Reactive Co-Sleepers
Practical reasons, such as a lack of space, may account for the development of some
parent-child co-sleeping arrangements (Germo et al. 2007); however, the decision is
often a reflection of parenting strategies or philosophies. Two forms of parental co-
Hum Nat

sleeping have been identified: early co-sleepers, and reactive co-sleepers (Keller and
Goldberg 2004). Early co-sleeping parents plan to co-sleep from birth, or begin to do so
within the first months of their child’s life. These parents report a satisfaction with
sleeping arrangements (Germo et al. 2007) that appears to be congruent with parenting
beliefs (Goldberg and Keller 2007). Reactive co-sleeping parents, however, use co-
sleeping as a palliative response to nighttime sleep problems, including sleep-onset
difficulty, frequent or prolonged night-waking, and intense crying. These parents tend
to be dissatisfied with the sleeping arrangements (Germo et al. 2007), to rate waking at
night as significantly more problematic despite no significant difference in frequency
compared with other co-sleeping families, practice more co-sleeping for part of the
night only, and usually begin co-sleeping when the child is one year or older (Keller
and Goldberg 2004).
Similar to early-co-sleeping parents, pet owners may have made the decision to co-
sleep with their pet from the time of adoption. This could be due to a lack of alternative
sleeping spaces, a conscious decision to be close and develop a strong relationship with
the pet (as noted above), or in order to ease the animal’s transition to the new household
(e.g., adopted or very young animals). Reactive co-sleepers may also co-sleep with
some pets but not with others, introducing them into the bed or bedroom to reduce
specific problematic behaviors. For example, the pet may be more distracting when
separated from their owner at night (Thompson and Smith 2014). Thus, the different
antecedents and consequences for these two co-sleeping groups need to be considered
separately, and they are in many cases applicable to human-animal co-sleeping as well.
One major point of difference, however, is that co-sleeping with pets is typically an
ongoing arrangement (i.e., for the life of the pet), whereas co-sleeping with children
decreases as the child ages, and eventually terminates at maturation and separation.
Attachment and Emotional Closeness
There may also be symbolic, relational, and visceral explanations for these similarities
and differences. For instance, parents who choose to co-sleep with children often regard
the arrangement as a form of parent-child interaction, providing security and an
opportunity for bonding time (Ball 2002; Welles-Nystrom 2005). Parents interviewed
in one study often co-slept with their infant for practical reasons, such as breastfeeding
and alleviating or managing sickness, or mitigating risk of SIDS, although reasons of
psychological security were also offered (Ball 2002). Ball (2002) further proposed that
co-sleeping could remove distancing effects felt by fathers and assist in increasing
paternal involvement. Overall, co-sleeping with spouses and children has been regarded
as protective, comforting, and vital to foundational relationships and emotional patterns
of family life (Worthman and Brown 2007). As noted above, the social guidelines of
who sleeps with whom reflects broader sociocultural values around belonging, identity,
care, and intimacy.
Of additional note is an apparent link between infant sleep patterns and infant
attachment status. McNamara et al. (2003) found that infants classified as insecure-
avoidant exhibited significantly fewer night wakings (at 6 months) and shorter dura-
tions of night-waking episodes (at 15 months) relative to their insecure-resistant
counterparts. Importantly, the relationship between sleep and early infant attachment
also reflects certain unique features of early infant sensory and motor integration,
Hum Nat

learning, communication, and motivation, as well as the regulation of biobehavioral
systems by the maternal caregiving interactions (Hofer 2006).
In ways comparable to the aforementioned reasons humans co-sleep with romantic
partners and children, pets can provide a source of comfort, companionship, and act as
substitutes for human social support (Beck and Madresh 2008). For example, some dog
owners consider their dog to be a member of the family, suggesting they should have
the same rights and privileges as a family member (Brown 2002). Other pet owners
may take this view a step further, perceiving their relationship with their dog as they do
with children, and will often interact with their dog accordingly (Archer 1997;Belk
1996;Brown2002; Veevers 1985). Interestingly, some dog owners choose to let their
dog(s), but not their child/children, sleep on their bed. If animal owners view their pets
as human substitutes, it makes some sense to regard human-animal co-sleeping as
another social dimension of sleep. Unfortunately, no study has yet considered these
potential motivations for co-sleeping; whether pet owners who currently co-sleep with
their pet have previously done so, or currently co-sleep with their children; and the
degree to which children and pets are comparable in this context.
Attachment theory might offer one explanation for why certain animal owners want
to co-sleep with their pets: to remain “close,”feel secure, and avoid separation anxiety
experienced by either the dog or owner (Archer 1997; Thompson and Smith 2014). In
its original form, attachment theory explains interpersonal experiences of affectional
ties between children and adults; however, it now also encompasses adult-adult rela-
tionships (Thompson and Smith 2014) and human-animal relationships (Beetz et al.
2012;Kurdek2008). Animal owners frequently turn to their pets for social support in
emotionally stressful situations (Kwong and Bartholomew 2011; Trigg et al. 2014,
2015,2016).
Attachment behavior is often used to describe any form of behavior that results in a
person attaining or maintaining proximity to a caregiver (or attachment figure) and is
most apparent whenever the person is sick, fatigued, or frightened (Bowlby 1982).
Essentially, attachment consists of two major, but separate, dimensions: anxiety,which
consists of the individual worrying about the attachment figure being unavailable
during times of distress, resulting in the person endeavoring to be close to them; and
avoidance, where both emotional and behavioral independence from the attachment
figure is sought and experiences of closeness and dependency are discomforting
(Kurdek 2009). Typically, when people cannot easily maintain contact with an attach-
ment figure, characteristic attachment behaviors arise; separation anxiety, contact
maintenance, and proximity seeking (Kurdek 2008; Zilcha-Mano et al. 2011,2012).
Thus, the role of attachment in co-sleeping behavior suggests that some humans may be
unconsciously motivated to co-sleep with their pets in order to feel secure and avoid
separation distress (Thompson and Smith 2014).
Indeed, there is preliminary evidence that dog owners who allow the animal to sleep
in their bedroom exhibit higher global attachment to the dog than do those who ensure
that their dog sleeps elsewhere (Martens et al. 2016). Whilst this interpretation of
attachment theory, and of seeking emotional closeness, has the potential to explain
human-animal co-sleeping, there is no universal consensus of what constitutes pet
attachment. The degree of attachment between a dog and its owner depends on the
owner’s needs and the dog’s personality and behavior (Brown 2002; Woodward and
Bauer 2007). Zilcha-Mano et al. (2011) propose that pet owners’different dispositions
Hum Nat

or orientations influence the way they experience relationships with their pets, and that
these differences contribute uniquely to the prediction of expectations about the pet and
emotional reactions to their death. Further, attachment theory does not take into account
individuals who feel securely attached or emotionally close to their dog yet feel no
need or desire to share their bed with their dog. Nor does it consider owners who
sleep with a dog because it is their partner’s dog and choice, rather than for the
reason that they themselves are securely attached to the dog (Smith et al. 2014;
Thompson and Smith 2014).
Pets as “Extended Selves”
The idea that animals (primarily companion animals) can be viewed as “extended
selves,”as proposed by Belk (1988,1996) and later Brown (2007,2011), provides a
more phenomenological explanation for close relationships between humans and
animals and offers one explanation for why people take risks for the animals in their
care (Thompson 2013). That is, the relationship with a pet can be so important to the
identity of some humans that pets might be best understood as special cases of extended
human selves (Belk 1988). In a sense, the animal can be viewed as an extension or part
of human self, wherein animals, analogous objects, money, other people, and so forth,
can be used in defining and developing human identity. Likewise, Thompson and
Smith (2014) propose that if a pet were considered an extension of a particular human,
it would not be surprising if it accompanied that human self in sleep. In particular,
owners who are unable to accompany their pets during the day might attempt to
maximize contact and interaction through co-sleeping during the night. A similar
explanation is provided by some working mothers when describing reasons for
sharing a bed with their child at night. In this case, co-sleeping can account for
lost time with their infants during the day, validate their maternal role, and ensure
that their infants know that their mothers love them and want to be with them
(McKenna and Volpe 2007).
Transitional Objects for Solo Sleeping Practices in Children
Thompson and Smith (2014) further suggest that pets can play a role as transitional
objects (or subjects) to encourage independent sleeping practices among children who
would otherwise seek comfort and security by sleeping in their parents’or siblings’bed
(also see Triebenbacher 1998). The term originally applied to objects such as blankets
and comforting toys to which children develop a strong attachment, but pets may also
be perceived by children as “living security blankets,”helping to mediate the connec-
tion between the child’s inner mind and outer reality (Lee 2008;ThompsonandSmith
2014; Triebenbacher 1998). The pet is independent, because it has its own character-
istics, but also becomes a part of the child as it takes on qualities projected by the child
(Noonan 1998). Transitional objects hold particular importance to children because
they provide the child with comfort and help alleviate anxiety or distress
(Triebenbacher 1997). Consequently, in the role of transitional objects, pets may assist
in the development of independent sleeping practices as they serve comfort and security
functions that children would otherwise seek in parental interactions (Thompson and
Smith 2014; Triebenbacher 1998).
Hum Nat

Conclusion
Apart from its clear reproductive function for the survival of the species, as well as
physiological support for the quality and quantity of sleep that are essential to individ-
ual health and well-being, co-sleeping fulfils basic psychological needs and reinforces
and maintains social relations. Throughout history, humans have shared their sleeping
spaces with other humans and other animals. However, the study of co-sleeping
practices is anthropocentrically framed: it is heavily biased toward interpersonal co-
sleeping to the neglect of interspecies co-sleeping. The result is an incomplete under-
standing of overall co-sleeping practices.
In the absence of targeted experimental research into motivations for human-animal
co-sleeping, this review has identified potential explanations through existing theories
of adult-child co-sleeping. Empirical research is required to determine how the con-
cepts of early co-sleepers, reactive co-sleepers, attachment, emotional closeness, ex-
tended self, and transitional objects apply to human-animal sleeping. Where existing
theories do seem to accommodate human-animal sleeping, there is a further need to
determine in what ways, under what circumstances, and what precisely they might
contribute to human society and development.
Existing theories and concepts need to be adapted or redefined to accommodate
some important differences between adult-child and human-animal co-sleeping. For
example, whereas co-sleeping with a child characterizes the early developmental stages
of adult-child relations, co-sleeping with a pet is likely to occur for the life of the pet. In
a household of pets, partners, and children, animal bedfellows often remain after other
humans have left. Finally, since our propositions are based on canine-centric research,
we also recommend detailed examination of human co-sleeping with other animal
species, particularly cats, but also less conventional species. Given that sleep accounts
for a large portion of human and animal life, and that interspecies co-sleeping impacts
humans, animals, interpersonal relations, and interspecies relations, there is an urgent
need for researchers to truly contemplate “who’sbeensleepinginyourbed?”
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Dr. Bradley Smith is a senior lecturer in psychology at CQUniversity. He is interested in all facets of the
relationship between humans and both wild and domestic animals. Over the past decade, Bradley has focused
his research on the cognition, behaviour and domestication of canids.
Peta Hazelton has a bachelor of psychology (honours). She is interested in all aspects of the human-animal
relationship, particularly on interspecies co-sleeping. She currently works as a support worker in Integrated
Family Services.
Kirrilly Thompson is a cultural anthropologist at CQUniversity’s Appleton Institute. She uses ethnographic
methods to research the cultural dimensions of risk-perception and safety, especially around human-animal
interactions. Kirrilly has particular interests in human-animal interactions, behaviour change, high-risk
interspecies activities and equestrianism.
Joshua Trigg’sresearch centers on theoretical and applied approaches to understanding human and non-
human animal relationships. His background is in psychology where he examines the roles that human/
companion-animal bonds plays in motivating and inhibiting early natural hazard preparedness and risk
behaviour by animal guardians in Australia. He is a current PhD candidate researching at the Appleton
Institute for Behavioural Science, Central Queensland University, Australia.
Hayley Etherton’sprimary research focuses on children, youth, families, and sleep. Her work aims to
advocate for the needs of families within their unique contexts to improve health, development and well-
being. She has a Bachelor of Psychology (Honours) and is a current PhD Candidate at the Appleton Institute
for Behavioural Science, CQUniversity.
Sarah Blunden (MAPS, BAPsych Hons, MSocSc, PhD) is a clinical psychologist, Head of Paediatric Sleep
Research at the new Adelaide campus of Central Queensland University, The Appleton Institute, Director of
the Paediatric Sleep Clinic, and founding Director of the Australian Centre for Education in Sleep. She has a
keen interest in early childhood sleep and development of the mother/child dyad relationships.
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