Dog breeds can be looked at like wild island populations, as long as we take care to coordinate assumptions and quantify terms. In breeds, the virtual island is the stud book and immigration to the island only happens when the stud books are open and breeders bring in fresh blood.
A fundamental fact of population genetics is that in closed populations (i.e., without immigration) the presence of only a small number of individuals, sustained over several generations, will lead to the depletion of genetic variation. Thus, the number of individuals is a crucial parameter in determining the amount of genetic variability that can be maintained in a population. This, in turn, influences the probability of long-term survival of a population because genetic variation is requisite for evolutionary adaptation to a changing environment. Thus, maintaining the population numbers and genetic variation must be a central theme of plans for long-term population management.
– Viable Populations for Conservation, Soulé
Chapter 6: Effective population size, genetic variation, and their use in population management; Lande and Barrowclough
In the context of population genetics, every single dog breed was founded by “only a small number of individuals.” Even ones where official stud books show hundreds of “founders.” Hundreds are small numbers in terms of population genetics, and even if we have a stud book with several hundred founders, they are not ideal founders, they are likely already related with many alleles in common, many alleles in saturation, and many genes with only one allele.
Except for definitional hybrids like Longdogs, Lurchers, and Designer Dogs; all breeds also fit the next condition: sustained closed breeding over several generations. This is absolutely true for breeds within closed registries and it is substantially true even for dogs in “open” registries.
To my knowledge, the last non-Border Collie to be Registered on Merit with the ISDS was a Bearded Collie named Turnbull’s Blue in 1984. I’ll write more about him later.
So our breeds exist as closed populations, with a small number of individuals, and this is sustained over many generations. Thus, it’s no surprise that we see the depletion of genetic variation.
And this last bit is so important, it’s worth saying twice.
Genetic variation is a requirement for evolutionary adaptation to a changing environment.
It’s not only that we should strive to give dogs the genetic capital to survive the great arc of history and the imperceivable progress of evolution, but we should likewise seek to preserve and and cherish their versatility and diversity that we haven’t already squandered.
The more traits, qualities, and abilities we appreciate the more likely those traits are to survive to the next generation and beyond. One trick breeds live and die on that trick. So a diversity of purpose as well as a diversity of genes are essential tools for the long term survival and health of our breeds.
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