Canis lupus familiaris
domestic dog facts

Dog origin and domestication

• First domesticated animal

  Dog is arguably the earliest animal domesticated by humans. Dog ancestors probably started to circle around temporary settlements of ancient hunters/gatherers for food scraps well before development of agriculture (the time when most of the animals and plants were domesticated). Perhaps, the first advantage of having them around for humans was the opportunity to collect information about changes in surroundings by observing the dogs' behavior. Thus, perhaps most ancient function of dogs in life of humanity was serving as a sentinels, which remains relevant up today.

• Two phases of domestic dog evolution

  1. They evolved as a species distinct from their ancestral form. Based on calibration point between the wolf and coyote and a mitochondrial molecular clock, time since divergence between the wolf and domestic dog was estimated to be between 76,000 and 135,000 years ago.
  2. They diverged into various breeds that have their distinct behavioral and morphological characteristics. However, it was not until 200-300 years before present that the majority of dog breeds were established leading to approximately 400 varieties. Most ancient dog breeds with most genetic similarity to wolf's are dingo, NGSD, Chow-chow, Shar-Pei, Akita, Alaskan Malamute, and Siberian Husky.

• Archeological evidence

  Fossil evidence places dogs in close proximity with humans as early as 31,000 years before present in a cave located on territory of Belgium. Additional evidence was found in France placing dogs with humans 26,000 years ago, and dog-like fossils have been found in Russia dated approximately 13,00-17,000 years before present. In all of these sites, the dog fossils are as large or larger than modern wolves, making the classification as domestic dog difficult and controversial.
  Small dogs were first found in burial sites in the Levant area of Israel, south of the Mediterranean, dating approximately 12,000 years ago. Overall, multiple line of evidence suggest that Middle East was critical for breed development through selection of specialized morphologic traits including size which is associated with mutation at insulin-growth factor (IGF1) locus found exclusively in wolves from this region of the world.

• Wolf is an ancestor

  Darwin wrote
  "I do not believe, as we shall presently see, that all our dogs have descended from any one wild species".
  Phylogenetic analyses derived from molecular markers support an origin of the domestic dog from one ancestor, the wolf, Canis lupus, thus refuting Darwin's hypothesis. However, most studies of variation at the mitochondrial control region suggest origin of dogs from different wolf stocks followed by introgressive hybridization between dogs and wolves (most often, female dogs and male wolves). Most modern domestic breeds share genetic signatures, to the greatest extent, with wolves from Middle East. However, breeds like Akita has more in common with Chinese wolves whereas European breeds such as Staffordshire bull terrier have more genetic similarity with European wolves. Wolves continue to influence the genetic diversity of dogs. In the United States, over 100,000 wolf-dog hybrids exist. Dogs genes may also be influencing the genetic composition of wild wolves. In Italy and in Spain, gray wolves interact and may interbreed with semi-feral populations of domestic dogs which may threaten the genetic integrity of wolf populations.
• All Canis species, as well as the dhole and the African wild dog, have identical chromosome numbers (2n=78), and all species in the genus Canis are known to hybridize. However, only grey wolves (Canis lupus) have been suggested to be the ancestor of domestic dogs and golden jackals (Cuon aureus) to contribute to dogs' gene pool.
  Dogs' brains are smaller than those of their ancestors, wolves. The reduction of the brain may be result of morphological modifications undergone by various dog breeds. Also, dogs' dependence on humans for food and shelter and in many cases for critical decision making in various circumstances could have contributed to more "economical" brain size. However, dogs have many advantages as cognitive research subjects because they are enthusiastic and cooperative, they enjoy being with people and follow their commands.

• Evolution of social cognition hypotheses

  • Canid generalization hypothesis. Wolves live in cooperatively hunting social groups, making it likely that they need to interpret the behavior of conspecifics and quarry alike, and this ability may then generalize to humans. This hypothesis predicts that many canids (especially wolves) should perform at least as well as dogs on social tasks.
  • Human exposure hypothesis. The domestic dogs are learning their skills during their individual ontogenies. This hypothesis predicts that variation in individual dogs' experience with humans will be associated with variation in task performance; and that young dogs should have relatively poor skills.
  • Domestication hypothesis . There has been selection pressure on dogs during the process of domestication for specific skills of social cognition and communication with humans. This hypothesis predicts both that dogs should be more skillful than wolves and that variations in experience with humans should not affect the performance of either species.

• Dog's genome

  Dog's genome consists of large number of small acrocentric chromosomes (2n = 78). It has been suggested that there is a relaxation of selection after domestication, leading to the build-up of a large number of non-lethal mutations serving as a raw material for artificial selection. In the wild, these mutations are usually cleared through purifying selection.
  Dogs, like cats, enjoy extensive medical surveillance that is second only to human health care. There are over 370 inherited disorders in the purebred dog population. Some 360 of them are also observed in humans. Of the identified disorders in which the mode of inheritance is known with reasonable certainty, more than half are identified as autosomal recessive. However, some important heritable defects, such as hip dysplasia and osteoarthritis in dogs, involve multiple genes and environmental factors.

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Dog breeds' diversity

• Breed definition

  A breed is defined as a group of organisms having common ancestors and certain distinguishable characteristics developed by artificial selection and maintained by controlled propagation. Although most modern breeds have existed for fewer than 400 years, each has its own distinctive characteristics. Fixation of the phenotype by breeding closely related individuals resulted in morphology, behavioral characteristics, set of inherited diseases, and variation in life expectancy specific to a particular breed. There are 157 U.S.-recognized breeds of domestic dog.

• Size diversity of dog breeds

  Two order of magnitude difference in size between Chihuahua (0.5 kg) and Great Dane (80 kg) is often cited as an example of intriguing phenotypic diversity of domestic dogs. Similarly, heights vary from nine inches (Pekingese) to three feet (Irish wolfhound).

• Life expectancy

  The size is one of the traits closely associated with life span. In a study of over 52,000 dogs, the likelihood of reaching 10 years of age was greater than 85% for Poodles, 75% for mongrels and Beagles, and only 30% for Burmese Mountain Dogs. Unrelated to their size, the shortened average lifespan of Cavalier King Charles spaniels, Irish wolfhounds, and Great Danes, for instance is due to a high risk of cardiomyopathies.

• Behavioral variation

  Differences between breeds that herd versus guard livestock illustrate breeds' behavioral diversity. Herding breeds, such as border collies, are used to manage the movement and behavior of livestock. Guarding breeds, such as the kuvasz, live among the livestock, usually unattended, and guard against predators. Both types of dog have been developed to work with livestock; however, they present radically divergent behavioral responses: herding dogs express predatory motor patterns such as stalking and some breeds (for example, Australian cattle dog) exhibit grab-biting behavior; whereas, guarding breeds do not chase, stalk, or even attempt to play with livestock.

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Feeding habits

• Diet of canids

  Most species within the dog family Canidae are predators and must receive dietary protein from prey, which may consist completely of invertebrates in such species as fennec fox or crab-eating fox. Members of genus Canis are considered to be omnivores with wolves being more dependent on meat than jackals and coyotes who can subsist on fruit and other plant material when prey is scarce.

• Dog feeding behavior

  Due to diversity of modern dogs it is always risky to generalize about "the dog" regarding any aspect of behavior including feeding. In contrast to cats, hunting behavior in domestic dogs in general and in some specialized breeds in particular (for example, hounds, retrievers, fox terriers, etc.) was greatly modified in comparison with the wolf, and most dogs are not capable of hunting for food. Feral dogs usually subsist by scavenging. However, several breeds of dog have a reputation for being able to consume large meals very rapidly, which possibly is the legacy of competitive feeding in the wolf.

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Dog vocalizations

Origin of dog-specific bark (selection pressures)

Barking is most commonly recognized as hallmark vocalization of domestic dog.

• May have been modified according to so-called motivational-structural rules of vocal communication in mammals (Morton, 1977 (.pdf)): concept of convergence of many animal sounds used in "hostile" and "friendly" contexts, for example, harsh low-frequency sounds when threatening and hostile and pure tone-like when frightened or suffering. In accord with this concept, the barking in many animals, including the domestic dog, is probably associated with mobbing and the motivational states that accompany mobbing (Lord et al., 2009).
• May play role in human-dog communications (similarly to domestic cats that have modified vocalization (cats' vocalizations at GeoChemBio)).
• Is affected by learning through the process of ontogenetic ritualization (Tomasello et al., 1994 (.pdf)): young animals not only learn imitatively their communication modes from conspecifics, but also individually conventionalize them with each other.
• Evolved under constrains of anatomical and physiological factors of ancestral vocal apparatus (vocal fold length and thickness, etc.).

Why dogs bark more than other canids?

• At the beginning of domestication, humans could have specifically selected dogs that barked more, for instance, as an alert function.
• Barking could have increased through indirect selection, i.e. in selecting for some other trait such as tameness, humans could have inadvertently selected for barking. This hypothesis is supported by Dimitri Belyaev's fox domestication experiment. Belyaev started with fearful foxes and selected only for tameness. After 30-35 generations, most of remaining foxes were as tame as dogs. Additionally, a small percentage had floppy ears and piebald coats, and many of them vocalized more frequently.
• Excessive nervousness and noisiness can decrease survivability of animals in the wild. Disadvantaged dogs supported by "forgiving" humans had a chance to reproduce and barking as well as other deleterious traits could persist for generations. Thus, in the absence of negative selection and as a result of permissive environments, excessive barking could gradually develop in some breeds as a natural way of animal to express itself vocally in times of stress, excitement, etc.
• Regardless of how increased barking evolved, at some point humans directly selected for barking in some dogs and against barking in others. For example, livestock guarding dogs are specifically bred for their barking and vigilant behavior whereas some hunting breeds are selected to be silent while working.
• Captive environment may contribute to development of barking in dogs by indirect reinforcement. For example, when postal carriers evoke barking by entering the dog's territory and then leave while dog is still barking, they reinforce the behavior. When dog that wants to go outside attracts owner's attention, owner reinforces the barking by paying attention and letting the dog outside.

Comparison with other canids

Dogs are different from their closest relatives, wolves and coyotes, in that they use barking in a wider range of circumstances than the other two who use barking mainly in defensive position or as a warning signal. Jackals, and especially foxes, exhibit a wider range of vocal signals than wolves and dogs.

Vocal repertoire of canids

Dog vocalization modes can be classified on the basis of acoustic properties (frequency, roughness/noisiness and rythmicity) as well on the basis of their functionality.

• Grunts Used in greeting and contact seeking by dogs and wolves
• Whines Used by dogs, wolves and coyotes in greeting, submission, defense, contact seeking, pain, loneliness and in group (pack). Dogs also may use in play initiation.
• Yelps Used by dogs in greeting, submission, defense, contact seeking, pain, loneliness. Coyotes also may yelp in pain and in contact seeking.
• Screams Used by dogs as well as wolves in submission and in pain. Coyotes, wolves and foxes may use in defense. Foxes may scream also in greeting and contact seeking.
• Howls Used by dogs and wolves in greeting, loneliness and in group (pack), by coyotes in loneliness and in group. Wolves also howl in defense.
• Growls Used by dogs, coyotes, wolves in defense, to threaten and in group. Dogs may also use in greeting and in pain. Foxes growl in defense and to threaten.
• Yaps Used by dogs, coyotes, wolves and foxes in defense and to threaten.
• Snapping the teeth Used by dogs and wolves in play initiation, defense and to threaten.
• Pants Used by dogs and foxes in play initiation.
• Barks May be used by dogs (breed-specific) practically in all contexts except in submission. Some breeds do not show any propensity to bark (for example, Basenji, Chow-chow, Shar-pei). Barks are also used as threatening signal by wolves, coyotes and foxes.

Foxes also have meows, bleats and clicks in their repertoire.

Source (modified): J. A. Cohen, M. W. Fox. Behavioural Processes (1976). Vocalizations in wild canids and possible effects of domestication.

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More about dogs at GeoChemBio

• Dog reproductive cycle (mating, estrous cycle)
• Dog development (from fertilization to adult)
• Dog taxonomy (full taxonomy of Canidae)
• Canine behavior (life with humans)
• Dog-to-dog communication (canine language illustrated)
• Bibiography (research articles and reviews)

Dog dieseases at MetaPathogen

• Dog hookworm (Ancylostoma caninum)
• Heartworm (Dirofilaria immitis)
• Canine Distemper Virus (CDV)

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