Social Behavior of Dogs

The origin of the domestic dog remains a mystery. Genetic studies and fossil records show that dogs arose from wolves between 11,000 and 16,000 years ago, during the Pleistocene epoch before the development of agriculture. The wolf species from which the dog evolved is likely extinct and has yet to be identified (1, 2).

Contemporary wolves and dogs are closely related phylogenetically, as a result of common ancestry and later interbreeding. Therefore, today’s gray wolf is an excellent proxy for comparing lupine and canine behavior traits (1, 3).

Both a single domestication event and multiple events have been suggested by genomic studies of wolves and dogs (3).

One of the most remarkable aspects of canine behavior is the ability of dogs to thrive in mixed-species social groups. When given a choice, dogs appear to prefer relationships with humans (4).

The question of how dogs came to associate with humans remains open. Popular notions that domestication occurred as a result of wolves’ attraction to human waste dumps and subsequent selection and breeding of more sociable individuals by humans are being reexamined in light of new data (5, 6).

Some researchers posit that the domestication of dogs was made possible by the evolution of social tolerance and attentiveness toward conspecifics and humans (7). Others posit that domestication occurred because dogs evolved characteristics that enable them to exploit human caring.

A study of the morphological differences between wolf and dog eye muscles demonstrated that dogs, unlike wolves, can use their eyes to communicate social messages that trigger increased oxytocin concentrations in humans (8, 9).

For the past millennium, humans have selectively bred dogs to fulfill various functions, such as hunting and guarding, leading to an impressive variety of physical differences and behavior patterns (10). Nevertheless, there is as much behavioral variation between individuals within a breed as between breeds (10). Breed differences in behavior are confined primarily to the specific characteristics for which each breed was bred (5).

Determining the extent to which breed influences behavior in dogs is confounded by the genetic variation within breeds and the considerable effects of environment on individual behavior (10, 11, 12).Therefore, making assumptions based on breed (breed stereotyping) can lead to an inaccurate assessment of an individual dog’s behavior and hinder the ability to make appropriate recommendations. Of note, the size of a breed does not reflect its activity needs. Small terriers, for example, might be active working dogs.

Dogs are a gregarious species with a flexible, highly adaptable social structure. Unlike wolves, which form family groups (packs) composed of male-female breeding pairs and their offspring, domestic dogs form loose associations with unrelated dogs. It is common for dogs to bond with other dogs when introduced to one another either as puppies or as adults in a home environment.

Bonds between dogs are maintained by extensive social communication and play. Free-roaming dogs can be solitary or live in groups. Group sizes vary from two to six dogs (13). Agonistic interactions over resources are uncommon between dogs within a social group.

Despite persistence of the idea in popular culture, a dominance hierarchy does not describe dogs' social relationships with each other or with human companions. Priority access to valued resources is not fixed or linear. A dog’s access to a specific resource depends on the context. It is determined by the dog’s motivation to obtain the resource, perceived barriers to success, and previous learning (14).

A linear dominance hierarchy can be described only in relationships between conspecifics in which one individual consistently defers to another in all contexts. The purpose of a dominance hierarchy is to maintain social stability within a free-roaming group. Therefore, ongoing aggressive interactions among dogs in a social group are unlikely to be linked to linear dominance.

Canine social communication is complex and diverse. Dogs convey messages to other dogs and humans using visual signals (such as body posture, facial expressions, tail and ear positions, and piloerection), vocalizations, scents, pheromones, and touch.

Scent marking, enabling nearby and distant communication with other dogs, is a central feature of canine social communication. Dogs detect pheromones by wafting them into the vomeronasal organ with the tongue (15).

Although dogs are not known for visual acuity, their ability to perceive visual social signals is underrated. A study found that dogs can make inferences about another dog’s emotional state by observing whether the dog’s tail wags predominantly to the right or to the left (16).

The human ability to understand canine communication is limited by a lack of access to olfactory signals. With study, however, humans can learn to interpret canine body language, vocalizations, and touch signals.

Domestic dogs are nonseasonal breeders and have, on average, 2 heat cycles per year (range 1–4). Gestation lasts 60–63 days.

If a female dog does not become pregnant during estrus, she will experience hormonal changes as if she were pregnant. This is known as false pregnancy or pseudocyesis, which can be associated with overt physiological and behavioral changes, including lactation, nesting, and protective aggression of objects such as toys.

Castration in males has been shown to decrease roaming, mounting, and urine marking by 50% in 60% of dogs and by 90% in 25–40% of dogs. The effect of castration on aggression toward human and canine family members is less marked. A 50–90% decrease in aggression was noted in only 25% of dogs. Castration had little effect on aggression toward unfamiliar people (17). Castration was not found to prevent the development of aggressive behavior (18).

A framework of developmental stages based on the work of Scott and Fuller in 1965 is commonly used to characterize canine development (19). These stages can be described as sensitive periods in which the environment has an outsized effect on an individual dog’s behavior (20).

The timing of canine developmental periods corresponds to neural developmental milestones (21). The onset and duration of these periods are influenced by both genetic and environmental factors and should therefore not be considered absolute (20, 21).

Nevertheless, developmental stages provide guidelines for when puppies should be exposed to environmental and social stimuli for optimal social and emotional development (20, 21).

Veterinarians and their staff should work with breeders, trainers, and shelters to ensure that newly adopted dogs get off to the right start. By offering timely advice on preventing and constructively managing unwanted behaviors in puppies, veterinarians can prevent problems that can negatively affect the bond between dogs and their owners.

For new puppy owners, advice should include information about canine communication and normal behavioral requirements (eg, chewing, social play, object play, rest), socialization, setting up a safe and stimulating environment, and the principles and practice of positive reinforcement training.

Proper development of social skills is best accomplished by adopting puppies into the new home at approximately 8–10 weeks and beginning socialization as soon as possible.

New puppy owners should be encouraged to enroll their puppy in a puppy socialization class before it is 12 weeks old to expose it to various dogs, people, and other stimuli (eg, novel surfaces, noises, odors, moving objects, gentle handling) in a safe and controlled instructional setting.

To lessen the risk of contracting infectious diseases, some professionals have recommended delaying socialization until the puppy's maternal-derived antibodies wane (at 16–20 weeks of age) and the puppy vaccination series can be completed. However, postponing socialization and exposure to new experiences until a puppy is fully vaccinated misses the important socialization window, which can increase the risk that the dog will develop fear and anxiety-related problems later in life.

A study of puppy class participants found no difference in the rates of canine parvovirus infection between vaccinated puppies that did or did not attend socialization classes before the age of 16 weeks (25). Well-run puppy socialization classes can be a safe and effective way to introduce puppies to people, other dogs, and novel stimuli. Puppies may be enrolled in a well-run, indoor socialization class at 8 weeks of age.

In addition to being enrolled in formal socialization classes, puppies should be exposed to the environments and experiences they will encounter throughout their lives, such as grooming, car rides, visitors, and traffic sounds, so that they become habituated.

An effort should be made to avoid triggering fear when introducing novel stimuli. When a puppy shows fear, the puppy's caregivers should enhance its tolerance by gradually introducing the frightening stimulus at a nonthreatening intensity and pairing it with enjoyable activities, such as food treats and play, to foster a positive emotional response.

Puppies thrive on structure and predictability. Puppy owners should establish a daily routine that balances time spent meeting the dog's social and physical needs via exercise and play with time reserved for rest and solitary exploration via food puzzles and chew toys

Time spent away from the owner helps a puppy learn to be independent. This can be accomplished by teaching the puppy to rest on a mat out of view of the owner for gradually increased periods of time. Independence is also fostered by providing the puppy with activities, such as chewing or puzzle play, that it can enjoy on its own in a puppy-safe environment.

When the puppy cannot be effectively supervised, the household should be organized to promote success and prevent failure. By preventing undesirable behaviors while offering options acceptable to both owner and dog, owners foster their puppy's ability to make choices, decreasing uncertainty and anxiety, and ultimately preventing undesirable behaviors.

Oral behaviors ("mouthiness") are a common problem because puppies have a behavioral need for exploration and play. Therefore, providing constructive social activities that do not include mouthing or biting—such as tug games, retrieving, walking and running, chasing, hide-and-seek, playing with other dogs, training for rewards, and interacting with chews and food-stuffed toys—gives the dog something positive to focus on.

Veterinarians and veterinary staff should encourage puppy owners to start positive reinforcement training at a young age. Teaching puppies what to do (rather than what not to do) and setting up the environment to prevent unwanted behavior promotes the development of trust, confidence, and a strong human-animal bond. Providing guidance about training methods and ways of identifying qualified trainers is essential.

Because dog training is an unregulated industry in the US, dog owners might have difficulty distinguishing between qualified and credentialed trainers who use evidence-based methods and trainers whose approaches are outdated and lack scientific validation. Positive punishment and negative reinforcement do not help dogs learn alternative, desirable behaviors; instead, these approaches break down trust and increase the risk of fear, anxiety, and aggression.

The goal of training should be to establish good communication, build life skills (obeying basic cues, loose leash walking, etc), and reinforce good choices. Training that focuses on teaching puppies what to do (rather than what not to do) and setting up the environment to prevent failure promotes the development of trust, confidence, and joyful obedience.

• American College of Veterinary Behaviorists. Decoding Your Dog. Horwitz DF, Ciribassi J, Dale S, eds. Houghton Mifflin Harcourt; 2014.

• Miklósi Á. Dog Behaviour, Evolution, and Cognition. 2nd ed. Oxford University Press; 2015.

• Serpell J. The Domestic Dog: Its Evolution, Behaviour and Interactions with People. 2nd ed. Cambridge University Press; 2017.

• Scott JP, Fuller JL. Genetics and the Social Behavior of the Dog. University of Chicago Press; 1965.

• Martin K, Martin D. Puppy Start Right: Foundation Training for the Companion Dog. Karen Pryor Clickertraining; 2011.

• Also see pet owner content regarding normal social behavior in dogs.

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