For many of us the companionship of “man’s best friend” is a daily source of joy, providing a connection to nature that helps us to appreciate the more simple things in life.  However, dogs can also be a public nuisance, especially when bad behaved or aggressive.  Every

throughout the world millions of dogs are euthanized by veterinarians because of behavioral problems, such as aggression towards people and/or other animals.  In searching for reasons for these aggressive behaviors the blame is often put on certain dog breeds, which then receive the reputation as being vicious.  Which breeds are affected varies not only from country to country, state to state or city to city, but even from one decade to another.  For example, breeds that have been labeled as vicious in the U.S. over the past 70 years include the Bloodhound, Doberman Pinscher, Chow Chow, German Shepherd Dog, and more recently the Pit Bull.  Dog breeds with the reputation of being dangerous have been and continue to be the target of local banning campaigns in an attempt to legislate against ownership of the breed(s) in question.  In the last decade breed bans in European countries like Great Britain included mainly pit bull-type breeds (e.g. American Pit Bull Terrier).  In 2000, local breed-specific legislation reached its climax in the German state of Nordrhine-Westphalia where 42 dog breeds were either banned or their ownership restricted, after fatal dog attacks on people.

     While public policy has moved toward the banning of certain breeds in an attempt to protect the public from vicious dogs, many ethologists, veterinarians and veterinary organizations (e.g., the American Veterinary Medical Association) oppose breed specific legislation.  Reasons for such opposition are that such legislation does not improve the control of vicious dogs but rather discriminates against owners of breeds that have a reputation of being dangerous.  What is more, legislation against so-called “dangerous” dog breeds poses another serious problem: enforcement.  How do animal control officers determine whether a dog is a member of a breed in question?

     To understand the problem of determining an individual dog’s breed we first must look at the history of the domestic dog and the development of modern breeds.  Archeological evidence indicates that the dog was the first animal domesticated by hunters, gatherers and foragers of the last Ice Age about 14,000 years ago (Clutton-Brock, 1995).  According to the most wide-spread and accepted theory, the domestic dog “likely originated from a large genetically diverse population possibly derived from wolf populations existing in different places and at different times” (Vilà et al., 1999).  Although dogs are taxonomically considered a separate species (Canis familiaris), from a geneticist’s point of view they are not a true species.  In fact, researchers have recently shown that there is less genetic difference between dogs, wolves and coyotes than there is between the ethnic groups of the human species (Coppinger and Schneider, 1995).

     So what exactly is a breed?  Per definition, breeds are groups of related animals, which are sufficiently similar in their genetic make-up and physical appearance to produce physically similar offspring when mated with each other (Blood and Studdert, 1999).  For example, the mating of two members of the Golden Retriever breed will produce offspring with physical characteristics that resemble those of Golden Retrievers (i.e., golden coat color, dark-brown eyes, floppy ears etc.).  Most of the modern dog breeds have a recent origin, with many breeds having been developed only within the past 150 years (Dennis-Bryan and Clutton-Brock, 1988).  The development of breeds is based on artificial selection by humans, a process where dogs are selected for certain physical characteristics (e.g., coat color) or behavioral traits (e.g., guarding).  During this process dogs have become a morphologically diverse species that is unique among mammals (just think about the differences in size and conformation between a Great Dane and a Chihuahua).  Such morphological diversity has been maintained and perpetuated through breeding controlled by breed societies.  Each dog breed is managed by a national breed society (e.g., the American Kennel Club), which is organized under an international umbrella organization, the Fédération Cynologique Internationale.  The breed society maintains a register of the animals that are members of the breed and sets the standards for physical appearance that must be attained.

     Because of this focus on a high degree of phenotypic uniformity (coherent physical appearance) many breeds became closed gene pools during their development.  Therefore, low levels of genetic variability within a breed and the occurrence of breed-specific genes or haplotypes (DNA sequences) would be expected within most dog breeds.  The identification of genes or haplotypes that are specific for a certain breed would enable us to determine a dog’s breed scientifically.  However, comparison of DNA sequences among members of different dog breeds revealed that there are high levels of genetic variability within breeds (Vilà et al. 1999).  At least two reasons have been proposed for this finding.  First, the founding stock of our modern dog breeds was likely drawn from a large and genetically diverse pool of dogs (Dennis-Bryan and Clutton-Brock, 1988).  Many of our modern dog breeds were created by crossbreeding, e.g., Golden Retrievers are believed to originate from the mating of a Flat-coated Retriever with a Tweed Water Spaniel and interbreeding of the offspring with Irish Setter, Labrador Retriever and Bloodhound (Alderton, 1993).  Second, dog breeds were actually not as highly inbred during the development of our modern breeds as it was assumed.  Although the goal of high phenotypic uniformity within a breed led to closed gene pools at some point during the development of modern breeds, dog breeders occasionally outcrossed their purebred dogs to avoid negative effects of inbreeding on health and behavior (Ubbink et al., 1992).  Thus, the introduction of foreign haplotypes due to genetic exchange between breeds and the short history of our modern dog breeds hindered the accumulation of breed specific genes (Vilà et al., 1999).  In fact, genetic differences among breeds are so minute that we cannot currently identify an individual dog’s breed based on DNA analysis (Templeton, 1990).

     In summary, a dog’s breed cannot currently be determined by using scientific methods such as DNA analysis.  Identification of an individual dog’s breed based on papers from a kennel club relies on the integrity of the breeder and does not guarantee pure genetic ancestry.  “Breed-specific ordinances imply that there is an objective method of determining the breed of a particular dog, when in fact, there is not at this time” (Canine Aggression Task Force, 2001).  Thus, the usefulness of such legislation is highly questionable.

Dr. Cornelia Wagner, DVM, MS     September 9, 2002

References:

Alderton, D. (1993): Eyewitness Handbooks: Dogs. Dorling Kindersley Limited, London, UK.

Blood, D.C., and Studdert V.P. (1999): Saunders Comprehensive Veterinary Dictionary.  2nd edition, W.B. Saunders, Hartcourt Publishers Limited, London UK.

Canine Aggression Task Force (2001): A community approach to dog bite prevention.  Journal of the American Veterinary Medical Association 218 (11), pp. 172-1749.

Clutton-Brock, J. (1995): Origins of the dog: domestication and early history.  In: Serpell, J. (ed.) The domestic dog: its evolution, behaviour and interactions with people. Cambridge University Press, Cambridge, UK.

Coppinger, R., and Schneider, R. (1995): Evolution of working dogs.  In: Serpell, J. (ed.) The domestic dog: its evolution, behaviour and interactions with people. Cambridge University Press, Cambridge, UK.

Dennis-Bryan, K., and Clutton-Brock, J. (1988): Dogs of the last hundred years at the British Museum (Natural History). London: British Museum (Natural History).

Templeton, J. W. (1990):  Canine DNA fingerprinting: can it identify breeds? Journal of the American Veterinary Medical Association 196, pp. 1357, 1359, 1365.

Ubbink, G. J., Knol, B. W., and Bouw, J. (1992) The relationship between homozygosity and the occurrence of specific diseases in the Bouvier Belge Flanders dogs in the Netherlands-inbreeding and sisease in the Bouvier dog. Veterinary Quarterly 14, pp. 137-140.

Vilà, C., Maldonado, J. E., and Wayne, R. K. (1999): Phylogenetic relationships, evolution, and genetic diversity of the domestic dog.  The Journal of Heredity 90 (1), pp. 71-77.