...is pretty much my life. My fatal flaw is huge ego, no work ethic. I habitually talk big about things I know nothing about, always assume I'm right, and generally make an arrogant ass of myself on a regular basis. So please, take the following as it is intended: a need to get thoughts out of my brain so I don't lose the brilliant insight I just had, and in three months come back and wallow in how stupid and foolish I was.
I'm going to take a break from talking about dog training, which I have actually done a little, and talk about dog breeding, which I definitely know nothing about. I don't think I've ever actually touched a pregnant dog.
One of my hobbies is collecting and reading old dog books. I recently borrowed two on dog breeding from my kennel club's library.
Assuming they are indicative of the mindset of the time, the goal of breeding purebred dogs was to breed perfectly predictable animals. One book takes it to the logical conclusion and suggests that a truly "Pure" dog would be homozygous for every gene. AA bb XX, but not Aa bb Xx. Conceptually, if you selected the most fit alleles to breed for, you could have a perfect super dog that was the picture of breed type, healthy, and robust.
As the understanding of genetics has advanced, it has become clear that this is not only likely impossible (due to incomplete dominance and co-dominance, as well as polygenetic inheritance and mutation), it is a bad goal. In an extremely specialized environment - like laboratory or Antarctica extreme - it's possible that a completely Pure population of animals might survive or even thrive. When the window of survivability is narrow, minor variations are quickly extinguished. Low genetic diversity might keep the population more robust.
This is nothing like the environment we keep dogs in. Looking at the United States dog population as a whole, there is a huge amount of variability in the environments. Some homes are hot, some are cold, some cycle through both regularly. Some cycle through both irregularly. Some homes are active, some are inactive. Some are experienced homes, some are inexperienced. Some homes want highly specialized and predictable behavior patterns, some want generalized behavior and some want diluted behavior altogether. Lepto is a problem in some areas but not others. Conceivably, there should be enough genetic diversity across all dogs for there to be a dog to fit nearly any environment.
The value of well-bred dogs is predictability, not purity. Purebred breeding is a means to that end, not a goal in and of itself. If purity was the goal, Gatsby would be a valuable dog. I love the dog, but it's criminal that a dog like him was brought into the world on purpose.