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The Evolution and Domestication of the Dog

It is not hard to understand how many different ways dog’s companionship serves human needs today. Dogs, resulting from domestication enjoy a truly unique status as companion animals. No other domestic animal enjoys the comfort and companionship afforded the dog. However, understanding how dogs achieved such unique status one might want to study evolution and domestication theories to explain how this remarkable relationship developed. There are differing views how dogs evolved and domestication occurred based on current evidence.

The available evidence provided through academic studies of fossil remains, animal distribution, comparative anatomy, biology, and the natural environment has helped us understand how this process may have taken place. It is through these studies that we can draw better conclusions about the ancestry and domestication of the dog.

The theories: how might the dog have evolved?

Artificial selection suggests that early man was successful in taking wild wolf puppies: breeding them and eventually training them to perform tasks such as hunting and providing protection from other predators. These tame wolves selectively bred to more tame wolves eventually creating over thousands of years a new population now referred to as dogs. An anthropologist, Dr. Colin Groves has suggested “…the human-dog relationship could be almost as old as modern man…basing his hypothesis on recent DNA research” and concluding “…humans domesticated dogs and dogs domesticated humans” (Perspectives in Human Biology, 1999).

“Darwin described the evolution of life as a process of natural selection…a competitive struggle to survive.” Those able to survive with limited resources, competition for food and space, evading predators and disease; sustain unpredictable shifts in the environment, changes in climate, these individuals might possess characteristics that make them more likely to survive and reproduce (Encarta, 2004).

In Darwin’s Origin of Species he says, “[c]an it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of years?” He suggests, “…individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind” (Darwin, 1859).

The evidence

Archeological evidence

Archeological evidence indicates the domestic dog has been around at least 14,000 years BP (before present) and that domestication probably began in Europe and western Asia. However, “[t]he archaeological record cannot resolve whether domestic dogs originated from a single wolf population or arose from multiple populations at different times…circumstantial evidence suggest that dogs may have diverse origins”, according to Wayne (Vila et al.,1997).

Fossil remains from archeological sites in North China dating 300,000 years BP, a cave in south France dated at 150,000 years BP and a site in Kent, England dated at 400,000 years BP has provided evidence of bone fossils from early hominids and wolves located in close proximity. These sites provide possible evidence that a close relationship may have existed between early hominids and wolves prior to 14,000 years BP. What the exact relationship may have been still remains unclear.

However, according to Wayne and his associates at UCLA, domestication may have occurred as early as 100,000 years ago or more and early efforts of domestication may not have produced “significant morphological change in the protodog, thus explaining the absence of dog skeletal artifacts appearing before 14,000 years ago” (Vila et al.,1997).

Wayne and his associates hypothesis states, “…domestic dogs may not have been morphologically distinct from their wild relatives…the change around 10,000 to 15,000 years ago from nomadic hunter-gatherer societies to more sedentary agricultural population centers may have imposed new selective regimes on dogs that resulted in marked phenotypic divergence from wild wolves” (Vila et al.,1997).

Clutton-Brock agrees and says, “[t]hese tamed wolves were many generations away from the true domesticated dog, but they were its precursors.” Some of the fossil evidence shows “slight morphological differences from those of wild wolves”. These slight differences include a “shortened facial region…compacted teeth…metapodial and toe bones…more slender than those of wolves.” This evidence provides slight anatomical differences, which may support Wayne’s theory (Serpell, Chapter 2, 1995).

The earliest fossil evidence of domestication were found at sites in Oberkassel in Germany dating 14,000 years BP and a site in Israel dated to 12,000 years BP. The Israeli site, know as Ein Mallaha includes a burial site containing a skeleton of a puppy that had been buried with a human. Stone dwellings, evidence of grinding grain and tomb burials indicated the site was a permanent settlement. The fossil evidence indicates the inhabitants were likely early hunter-gatherers on the verge of becoming agriculturists. These permanent settlements likely provided the beginning of domestication of what we know today as the dog.

The remaining question on the origin for the domestic dog remains unclear. However, Lindsay says, “the dog is a domestic wolf” but the exact origin of its predecessors remains debated. Some think the Indian Wolf (Canis lupis pallipes) is the most likely progenitor of the dog. The conclusion based on a smaller size thus less threatening to early humans. Others have selected the Chinese Wolf (Canis lupus chanco) concluding the smaller size and mandible morphology supports, “the apex of the coronoid process turns back in both the Chinese wolf and the domestic dog but not in the jaw bone of other wolf species.” Still others have identified Canus lupus arabs, a western Asiatic wolf and the European wolf as the ancestor for most of the European breeds. According to the “genome of Arctic and European spitz-type breeds”, Canis lupus lupus has the greatest representation (Lindsay, 2000).

According to Clutton-Brock, “[t]he similarity in size and osteological characteristics of most of the remains of domestic dogs found on prehistoric sites in many different parts of the world may indicate that a small population of dogs diffused from a founder group in the early prehistoric period.” He maintains, “wolves must have been tamed and lived around human settlements in many parts of the world, and a single litter of puppies from any one of these could have provided the foundation stock for a large population of domestic dogs that subsequently became very widespread” (Serpell, Chapter 2, 1995).

Based on fossil evidence, locations of archeological sites and comparative anatomy the early prototype dog likely received diverse genetic influence from several wolf species in different regions and during different times. Lindsay says, “…the biological ancestry of the dog is now certain…based on both genetic and behavioral studies the dog is a domestic wolf” and agrees the closest relative remains unknown (Lindsay, 2000).

According to Coppinger and Schneider, there are several views on the true origin of the dog, with the most common and accepted being that Canis lupus, is the “wild progenitor,” while still another suggests the wolf with “…some degree of hybridization with other members of the genus Canis, particularly jackals and coyotes contributed to the present day dog. Still another possibility suggests the dogs’ origin may have originated from other modern primitive breeds such as the Australian dingo, New Guinea singing dog and the Asiatic and African pariah dog. However, some consider the origin of the dog a mystery and therefore any speculation is “premature” (Serpell, Chapter 3, 1995).

We can speculate the early progenitors were wolves and possibly included other members of the same species. According to taxonomy the wolf and dog are both members of the order Carnivora and classified in the family Canidae with coyotes, foxes, jackals, wolves and dogs and further classified in the Genus Canis, which includes wolves, jackals and dogs. All these members can interbreed and successfully produce offspring. According to Serpell, “no other group in the animal kingdom has achieved such a diversity of form in so short a time as C. familiaris.”

However, the “anatomical similarity” between the species does not provide the answer to the question of origin. According to Serpell, “…the real difference between them is behavioral: dogs are tamable and trainable, wild canids are not” (Serpell, 1995).

Biological evidence

Recent scientific discoveries in molecular biology and genetics have helped further explain how the dog may have evolved. To assist in explaining the biological process it might be helpful to understand a little about genetics. O’Heare provides the explanation as, “[a] genotype for a trait consists of the specific alleles that an individual possesses related to that trait…the term phenotype…describe[s] how that trait is expressed or displayed.” To explain this process further, O’Heare provided the following.

The genotype is the genetic blueprint and provides the instructions for the organism to produce proteins,
which then produce structures of the body. A genotype is the underlying genetic basis for a phenotype.
The proteins interact with each other and with the environment to form larger, more complex structures.
These proteins and structures are referred to as phenotypes. They are the physical, observable traits
produced by the genotype. The genotype (the blueprint) provides the potential for a range of possible
phenotypes (the result you see).

How this process helped the dog evolve is explained as “[w]hat is actually expressed within that range of potentiality will depend on how the environment interacts with the structures as they develop” (O’Heare, 2003).

“Evolution refers to changes in allele frequencies within a population of organisms over time…that individuals do not evolve…populations evolve” and as a result “…allele frequencies within the population change from generation to generation” (O’Heare, 2003).

Natural selection, O’Heare says, “…refers to the environmental influence on the reproductive success of some individual members of a population of organisms” and “…alleles from the reproductively successful organisms will be increased in the next generation and the alleles of the reproductively unsuccessful will alternatively decrease…variation in traits is common” (O’Heare, 2003).

Those individual traits affecting adaptability for a species might include “variable aggressiveness, size, confidence, and prey preference.” The more adaptable the trait, the more chance it will be passed on to the next generation. The “[a]daptive variations of traits are passed on at a greater rate than maladaptive traits…and with this inheritance come changes in the frequencies of the alleles involved from one generation to the next in the population.” This is what O’Heare refers to as evolution (O’Heare, 2003).

However, Mitochondrial DNA studies have not conclusively proven the exact lineage the dog derived from. Therefore, any assumptions would be pure speculation. However, we can be certain that the most likely trait facilitating the domestication process was the dog’s willingness to accept and live in close proximity to humans.

Evidence of domestication

Without any clear fossil evidence that dogs existed prior to 14,000 years ago one can only presume early man had a relationship with tame wolves as early as 400,000 years ago or later. The archeological and scientific evidence does not support or prove whether man utilized wolves in any role or whether any close, relationship existed.

The Natufian burial site at Ein Mallaha, containing a woman clutching what appears to be a tame wolf or dog puppy has significant cultural value. Another Natufian burial site located in Israel contained a man with two adult canids identified as dogs. This archeological evidence provides proof of domestication and a much closer partnership to early hominids. Considering these finds it may be unlikely dogs were domesticated prior to approximately 14,000 years ago.

What defines domestication?

Clutton-Brock explains the domestication process as “two interwoven processes.” The first biological process resembles natural evolution where the “parent animals become reproductively isolated from the wild population and form a small founder group…that will at first be very inbred, and which will undergo a process of genetic drift.” These founder groups would increase and genetically change through natural selection due to environmental changes and human influences. According to Clutton-Brock, “these tamed wolves would have become less and less like their wild forebears because inherently variable characteristics, such as coat colour, carriage of the ears and tail, over all size and the proportions of the limbs would have been altered by the combined effects of artificial and natural selection” (Serpell, Chapter 2, 1995).

The second “cultural process” began when early humans took possession and integrated these early dogs into their societies. Clutton-Brock says, “…the wolf became a dog…it was no longer a wild carnivore but a part of human society with physical characteristics adapted to its economic, aesthetic or ritual functions…with the latest phase…individual ownership…was enforced with a collar and leash” (Serpell, Chapter 2, 1995).

For a wild animal’s survival it is necessary to have a “high degree of perception…quick reactions to stress” and according to Clutton-Brock the opposite characteristics are necessary for domestic animals such as, “…docility, lack of fear and tolerance of stress” (Serpell, Chapter 2, 1995).

Biological and structural changes may take place, according to Clutton-Brock, such as “hormonal changes, reduction in size of brain, less acute sight and hearing, and the retention of juvenile characteristics and behavior into adult life” (Serpell, Chapter 2, 1995).

Behavioral characteristics of domestication

We know following the Ice Age, ending approximately fourteen-thousand years ago, Mesolithic societies “…began to gather for the first time in permanent settlements…coincidental with the first fossil evidence of dogs as we know them.” This created a “niche” for tamer wolves to domesticate themselves. Driven by a new and easily accessible food source, these tamer wolves may have been “genetically predisposed” having a lower threshold of “flight distance” thus enabling them a “selective advantage in the new niche over the wilder ones” (Coppinger, 2001).

Lindsay describes the early relationship of humans and tame wolves as “mutualism” between the two species. He says, “wolf-pack territories may have formed around human camps, thus providing a natural protective shield against the threat of predation by other less friendly wolves and competing human groups” resulting in “an ecological niche” which further facilitated the “protodog” to undergo “novel morphological and genetic changes gradually leading to domestic dogs” (Lindsay, 2000).

This type of close contact, according to Lindsay, “requires that the animal in question possess a high fear threshold and a reduced tendency to flee, essential behavioral characteristics of domestication.” The “scientific evidence for a genetically divergent distribution of temperament traits based on relative tameness and confidence among canids has been demonstrated” by the Belyaev fox studies (Lindsay, 2000).

According to these studies performed by Belyaev, he successfully bred “less fearful individuals” over several generations creating a tame “human friendly” fox. “Although a similar genetic basis for social tolerance has not been demonstrated in wolves,” it could reasonably be believed that a percentage of early wolves were less fearful and more tolerant of human presence. This “adaptive behavioral polymorphism in wolves and its relevance to domestication have been discussed in detail by Fox (1971) and Scott” (Lindsay, 2000).

It could be concluded from this evidence the single most significant trait “less fearful” contributed to what was described earlier by O’Heare as “…alleles from the reproductively successful organisms will be increased in the next generation and the alleles of the reproductively unsuccessful will alternatively decrease…variation in traits is common” (O’Heare, 2003). This single trait may have been all that was necessary to provide the tame wolf populations with what they needed to become more reproductively successful therefore passing on their genetic diversity.

From this, we could conclude that based on the archeological and scientific evidence and the behavioral characteristics the ability to live in close proximity to human settlements provided the variation necessary to further facilitate the adaptation of the tame wolf populations to the ever changing environment in which they lived thus perpetuating the ongoing evolution from wolf to dog.

Behavioral differences – between wolf and dog

As a result, of continued domestication it seems dogs have undergone considerable behavioral changes furthering them farther away from their now canine cousin the wolf. The domestic dog has transformed into a more docile and affectionate animal than the wolf. According to Lindsay, “…dogs have lost the lupine carnivorous drive and predatory behavior exhibited by wild canids.” Even though dogs prefer meat, their diets today can consist of a vast variety of foods, unlike what their “ancestral progenitors” may have eaten (Lindsay, 2000).

Other notable differences are that dogs “tend to mature physically and sexually much more readily than wolves…dogs become sexually mature around 7 and 10 months” and “wolves reach sexual maturity at approximately 22 months.” Additionally, “…dogs will readily mate with multiple partners, have biannual breeding cycles, and male dogs are fertile year round.” Wolves tend to be more “selective and monogamous,” having annual breeding cycles and at times other than during the breeding cycle the males testes atrophy “rendering the wolf infertile” (Lindsay, 2000).

Some distinct differences are the dog’s ability to alarm bark and scent mark. Wolves perform these behaviors, but less frequently. It is important to note not all-domestic dogs bark, Lindsay suggests the “…tendency to bark may be socially facilitated or learned.” He says, “Coppinger and Feinstein have disputed the functional and communicative value of the dogs barking behavior” and Lindsay says they have argued “…that barking behavior is poorly directed, excessively ambiguous, ‘indecisive’ – even meaningless.” He said, “…they conclude that the dog’s increased tendency to bark is an inadvertent symptom of domestication…rather than a genetically selected tendency” (Lindsay, 2000).

The dog’s excessive need to mark by urinary scent distinguishes them from wolves. This appears to be an excessive way to communicate and the exact cause is unknown. Some scientist have speculated it may serve to communicate territory, however according to Lindsay, “Scott (1967) argued that canine scent marking does not serve a territorial function, but rather functions more or less to communicate that the dog has been recently in the area” (Lindsay, 2000).

Other behavioral differences include the “…display of aggressive behavioral patterns” between the species. It has been noted that wolves “reaching sexual and social maturity, tend to compete much more aggressively and earnestly for social status.” Lindsay says, “fighting styles…differ significantly” noting that dogs “…tend to limit their attacks to the head, neck, and shoulder” and wolves tend to make better use of “body blocks…attacking extremities” rendering the opponent into a more vulnerable position (Lindsay, 2000).

A truly unique quality retained by the domestic dog is the typical dog’s willingness and tolerance to accept strangers. Wolves tend not to accept strangers even among their own pack. The typical wolf would be wary of human presence and tend to have a low threshold for flight. Today environmental pressure from humans continues to make it difficult for wolves to thrive in many regions of the world.

According to Lindsay, an important influence of domestication is the “attenuation of predatory instincts.” He says, “wolves possess a set of innate predatory behavior patterns that are readily evoked by an adequate stimulus…presented with a prey animal, wolves respond in a species-typical manner by emitting an appropriate series of behavior sequences.” The sequence of behaviors may include crouching, stalking, worrying, charging, pouncing, biting, and shaking. Presented with “…the same prey stimulus, dogs may do little more than play or tease the target animal” (Lindsay, 2000).

The question of intelligence between the species seems to separate some scientist, with some insisting wolves are more intelligent. According to these scientists, “…wolves must work for their living” and have considerable “…variations in proportional brain sizes.” Lindsay concludes, “…such speculation is fascinating” however he suggests, “it may be more productive to study relative intelligence among canids by comparing their performance under controlled conditions and discuss intelligence in terms of quantifiable learning skills and problem-solving abilities” (Lindsay, 2000).

One of the more endearing qualities of dogs is the tendency to retain puppy like characteristics well into adult life, most likely an adaptation of domestication. According to Lindsay, “…several behavioral changes can be detected in the direction of youthfulness.” He says, “…domestic dogs appear in many respects to act like 4- to 6- month-old wolf puppies.” The process of retaining these childlike qualities is known as neotony (Lindsay, 2000).

Lastly, wolves tend to form social bonds with humans in the absence of adult conspecifics and fear. On the other hand, dogs form attachments to humans easily, actually preferring human contact rather than conspecifics when given a choice. The reduced flight tendency resulting in tameness and acquired through domestication has aided in creating a strong motivation to seek social contact with humans.

The dog continued to evolve from the early protodog, eventually trained to herd, guard livestock and assist in hunting. Most recently, deliberate breeding processes selecting various desirable traits has given us over 400 recognized breeds of dogs. This diversity is unknown in any other species and truly makes the dog unique. Today, dogs serve us in many different functions and we continue to find more ways to utilize them every day.

References

Coppinger, Raymond, and Lorna Coppinger. Dogs: a new understanding of canine origin,
behavior and evolution
. Chicago: Chicago UP, 2001.

Darwin, Charles Robert. The origin of species by means of natural selection.
New York: Gramercy, 1979.

King, Christopher. “Evolution.” Microsoft Encarta Online Encyclopedia
2004.

Lindsay, Steven R. Handbook of applied dog behavior and training. 2 Vols.
Iowa: Iowa SP. 2000. Vol. 1.

O’Heare, James. Dominance Theory and Dogs:
Ottawa: DogPsych. 2003.

Marilyn Koyanagi. “Is human evolution a closed chapter?”
Rev. of Perspectives in human biology, by C. Loring Brace.
Natural Science 1, Nov. 1998.

Serpell, James, ed. The domestic dog: its evolution, behavior, and interaction with people.
Cambridge: Cambridge UP. 1995.

Vila, Carles, et al. “Multiple and Ancient Origins of the Domestic Dog.”
Science, 276, (1997): 1687-89.

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