Inbreeding: excerpt from my Middlesex research paper

The Psychology of Breed Specific Evolution, Selection and Behaviour

Editor Note:  Although the following was a minimal part of my research and lifted out of context of the project as a whole, I believe the information to be of value for those interested in learning more about the ‘science’ of breeding. 

…One unplanned direction of research was that of the breeder as there were a surprising number of dogs within a breed category that yielded curious, ‘uncharacteristic breed’ results, thus is was necessary to explore a further area of ‘human imposition’.

The evolution of breeds and effects of selective breeding and inbreeding

The development of a dog breed involves the breeding of a small number of select dogs and reproductive dominance of further dogs that confirm closely to the desired standard.  Such restricted breeding practices reduce population sizes which result in the increase of genetic drift[1] and decrease of genetic diversity.  The genetic variation is threatened further by bottlenecks associated with significant environmental and cultural events.  One example is that of the English Mastiff whose United Kingdom registration dropped to three by the end of the First World War[2] and the subsequent number of Mastiffs recorded during this era with information recorded as “unknown” or “unregistered” parents suggesting that dogs resembling a Mastiff and vouched as such by the breeder likely ‘tainted’ the original breed bloodline, (Baxter, 2004).  During the same time period the breed suffered to near extinction in the United States, (Hoffman, 2004), ultimately altering this breed (and other breed’s) appearance and character traits across continents.  The following quote from the American Kennel Club web site is a testament to the breed standard disconnect that arose from this particular bottleneck:


“Long-standing rules and regulations were interpreted more loosely and, in many instances, disregarded altogether.”

Over time enthusiasts assume control and re-construct their breed standard’s integrity, which was a practice that entailed extensive and repeated inbreeding.  Inbreeding was the result of scarce and desirable mating options, most especially for rare breeds.  Additionally, little was known in regards to genetic science and the implications thereof.  Inbreeding was also a reflection of the social attitudes of the time where purebred dogs represented wealth and a dog’s ‘conformation’ and appearance were primary driving factors for choosing mating partners.  As social attitudes change, so do the individual breed standards, and in many cases, the more exaggerated the unique features of the dog, the more attractive it is to own and subsequently breed.

The long-term effects of inbreeding are numerous.  Extensive use of a single stud or dam or generation thereof can accelerate loss of alleles[3] and skew the gene pool toward the alleles that the dog carries.  The dog is used because of their desirable traits, which will be more common, as will those for the lethal equivalents.  If a bad gene is linked[4] to a desirable one, the results may be complexly problematic.  Furthermore, and in relation to behaviour as well as health, loss of alleles and genetic drift can be so subtle it may be unnoticed by the breeder and innate behaviour such as herding ability and guarding instincts can be diminished if the breeder is not using the behaviour as part of their selection criteria.  To reduce the loss of alleles in the population, the breeder must have thorough knowledge of up to five pedigree generations.  Additionally, if two dogs do not share ancestors for four generations, but share many in the fifth and beyond, mating them would be inbreeding, (Sharp, 1999).

Similarly, selective breeding for appearance without regard to temperament will yield ‘breed flawed’ character traits which may constitute problematic behaviour and may account for inconclusive survey responses…


Diane Kunas, MA, MCFBA

Middlesex Research Project

Winter 2010

The Psychology of Breed Specific Evolution, Selection and Behaviour

pp. 26 – 27

[1] A genetic drift is the change in the frequency of a gene variant which over time may cause gene variants to disappear completely, thus reducing genetic variation.

[2] The Kennel Club registry for English Mastiffs in 1918.

[3] The DNA codings of an allele determine distinct traits that can be passed from parent to offspring.  A dog can only have a maximum of two alleles for any given gene, (Sharp, 1999).

[4] Sits close on the chromosome.


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