Dog Breeding: Canine Evolutionary History and Implications for Human Genetics
Since as early as 15,000 years ago, humans have played a part in the species differentiation between dogs and wolves. Dogs, or canis familiaris was the first species to be domesticated, at least several thousands years before any other animal or plant species (Leonard, Vila and Wayne). From centuries of selective breeding more than 400 distinct breeds of dogs have been produced that differ greatly in morphology (form and structure, such as body size, coat length and color), behavior, and disease susceptibility. (Parker, Sutter, and Ostrander). The holding of dog shows and the later establishment of the kennel clubs in Britain, America, and France in the late 19th and early 20th century have had a generative effect on pedigree dog breeding and showing throughout the world (Sampson and Binns). These breeds have developed not from natural selection, but from selection by humans for various uses in different societies, leading to different proclivities for certain behaviors like retrieving, herding, and guarding, between breeds. Natural selection and geographic separation may have also contributed to genetic differentiation, resulting in additional breeds. Even within a breed exists variability between individual dogs in their suitability as pets or working dogs, which reflects the heterogenic background of dog breeds (Giger, Sargan, & McNiegel).
The differences in cranial and skeletal proportions among dog breeds are greater than that among wild dogs. The great diversity in morphological variation found in dogs makes them excellent models for understanding morphological variation in humans. Domestic dog breeds exhibit great diversity in behavioral patterns as well as distinct behavioral patterns from their wild dog ancestors. In spite of this great diversity in phenotypic expression of traits, domestic dogs have diverged only recently from their wild ancestor, the gray wolf, and the two species have very similar genomes, or hereditary information. Only a small subset of genes has changed throughout the process of domestication and understanding this process has provided a unique window into how rapid diversification in both domestic and wild species. This wide variety of behavior, phenotype, and disease susceptibility displayed by different breeds, makes dogs an especially useful model for studying the traits that affect human health. In fact, more human disease syndromes have been observed in dogs than in any other domestic mammal, leading to a greater ability to characterize genes that influence phenotypic traits (Young and Bannash). Specifically uniformity within these breeds allows for identifying and mapping the genes involved in complex traits, especially those tied to disease susceptibility and progression (Parker, Sutter, and Ostrander).
The recent availability of the dog genome sequence has led to greater recognition of the importance of the domestic dog in identifying genes that determine basic aspects of mammalian development (Parker, Sutter, and Ostrander). Further, cognitive scientists have recently begun investigating special skills for reading human social and communicative behavior apparent in dogs than in other animals more closely related to humans, such as chimpanzees (Hare and Tomasello). Such a finding raises the possibility that convergent evolution has occurred, or that both Canis familiaris and Homo sapiens may have evolved similar social-communicate skills in both species for specific kinds of social and communicative interactions with humans (Hare and Tomasello). It could be the case that these two distantly related species independently evolved these analogous traits as a result of a similar evolutionary process. Thus if dogs’ social skills do in fact represent a case of convergent evolution with humans then insight into the selection processes that drove such evolution might allow for the development of testing whether similar processes shaped human cognition.
One example of the superior social-communicative abilities in dogs compared to chimpanzees has been found using the object-choice paradigm, in which an attractive object is hidden in one of several hiding locations in such a way that the subject does not know which location conceals the object. The human experimenter then indicates the location of the object. If the subject chooses the right container he is allowed to retrieve the reward, while if he chooses the wrong container, he is only allowed to see its true location. This procedure is then repeated between 10 and 20 times so as to compare the individual’s performance against chance and to give the subject a chance to learn the experimenter’s instructive behavior. All primates have shown poor proficiency at finding hidden food rewards by using social-communicative behaviors from humans. Dogs consistently show much greater awareness of even subtle indications from humans of where the reward is hidden. Other research has shown that dogs can gauge whether or not a human has visual access to his surroundings in a number of contexts. They have also consistently shown an ability to learn about their environments from humans from either communicative behaviors like pointing or noncommunicative behaviors like glancing. Such social inferences have only been observed in language-learning human children and not even in nonhuman primates (Hare and Tomasello).
The fact that domestic dogs exclusively, and not wild dogs or nonhuman apes possess these human-like social-cognitive skills raises some interesting possibilities, such as convergent evolution. Several possibilities have been postulated to account for this finding. One possibility is that such abilities arise from dogs having been socialized with humans. Chimpanzees raised from infancy with adults spontaneously use many social cues in the object-choice task. Some have suggested the possibility that dogs’ social-cognitive skills evolved during the years of domestication. Such a possibility has been explored in comparative studies of the genetics of domestication in foxes and dogs (Hare and Tomasello). Studies of mtDNA in dogs that began in 1996 has provided increasingly more accurate evidence for origin of dogs, for example providing evidence for a geographic origin in East Asia (Savolainen). Comparisons between wolf and dog mitochondrial control regions have also suggested that dogs arose through multiple events of domestication within multiple wolf populations. Such findings carry some interesting implications for human cognition: for example, some aspects of human-like social cognition may potentially evolve not specifically as adaptations, but instead as a result of selection on unrelated social-emotional systems like the limbic and endocrine systems and not the neocortex (Hare and Tomasello). These findings also suggest that humans’ social-cognitive abilities may have evolved in a similar way, that is, a kind of self-selection may have taken place in that a more human-like temperament was naturally selected for while overaggressive or despotic individuals were either killed or ostracized.
Dogs have also been found to show consistency in human-like personality traits over time. In a study by Svartberg, Tapper, Temrin, Radesater, and Thurman (2005), dogs were given behavioral tests three times over about three months. In response to 10 subtests exposing dogs to situations such as the appearance of an unfamiliar person, play, prey like objects, and metallic noises, dogs showed significant stability between trait scores for Playfulness, Chase-proneness, Sociability, and Bolcness. The scores for Aggressiveness and Curiosity/Fearlessness, however, differed between the first two tests, suggesting that these two traits in dogs are more sensitive to novelty.
Our close genetic relationship with dogs seriously puts into question the concepts of uniquely “human” constructs, such as “personality.” Dogs too display great stability in personality traits over time, personality traits that are central to the (at least Western) definition of humanity, such as extraversion, or sociability. The fact that distinct behavior patterns that vary between breeds can be tied specifically to biological factors reminds me of the discussions we have been having in class about personal accountability. If behavior patterns in mammals are largely genetically determined as well as environmentally, then this seriously threatens the existence of free will and thus accountability.
The fact that dogs can be bred to exhibit specific behavioral patterns and personality traits really causes me to consider whether human parental behavioral patterns and personalities can really be attributed very significantly to personal choice. We do not tend to hold a dog morally accountable for positive or negative behaviors associated with its breed (though we might prefer one breed over the other or euthanize an especially violent dog).
Through selective breeding we have created a species uniquely suited in its variation and within-breed uniformity for a greater understanding of our own genes, as well as a template for potentially understanding aspects of our own phenotypic expressions of genes. Study of the dog’s genome has led us to a greater understanding of genetic predispositions for disease and the general development in mammals of particular traits, as well as social-cognitive development in humans, suggesting interesting possibilities for the definition of human identity.
1) Giger, U., Sargan, D. R., & McNiel, E.A. Breed-specific Hereditary Diseases and Genetic Screening. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 249-290). Cold Spring Harbor, NY: 2006.
2) Hare, B., & Tomasello, M. Behavioral Genetics of Dog Cognition: Human-like Social Skills in Dogs are Heritable and Derived. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 497-514). Cold Spring Harbor, NY: 2006.
3) Leonard, J. A., Vila, C., & Wayne, R. K. From Wild Wolf to Domestic Dog. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 95-118). Cold Spring Harbor, NY: 2006.
4) Parker, H. G., Sutter, N. B., & Ostrander, E. A. Understanding Genetic Relationships Among Purebred Dogs: The PhyDo Project. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 141-158). Cold Spring Harbor, NY: 2006.
5) Sampson, J., & Binns, M. M. The Kennel Club and the Early History of Dog Shows and Breed Clubs. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 19-30). Cold Spring Harbor, NY: 2006.
6) Savolien, P. MtDNA Studies of the Origin of Dogs. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 119-140). Cold Spring Harbor, NY: 2006.
7) Svartberg, K., Tapper, I., Temrin, H., Radesater, T., & Thorman, S. Consistency of Personality Traits in Dogs. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 141-158). Cold Spring Harbor, NY: 2006.
8) Young, A., & Bannasch, D. Morphological Variation in the Dog. In E. A. Ostrander & U. Giger (Eds.), The Dog and its Genome (pp. 47-66). Cold Spring Harbor, NY: 2006.