From the link you posted: Breed
1. A race
or other animals
(or of plants
), perpetuating its special or distinctive characteristics
. Twice fifteen thousand hearts of England's breed.
(Shak) Greyhounds of the best breed.
2. Class; sort; kind; of men
, things, or qualities. Are these the breed of wits so wondered at?
(Shak) This courtesy is not of the right breed.
3. A number
produced at once; a brood
is usually applied to domestic
to wild animals
and to plants; and race
Race (or breed) as applied to humans is not a genetic construct. Yes, blacks have different characteristics than whites, but those distinctions are maintained either by lack of opportunity for inbreeding (distance) or prejudice. My wife was born and raised in the Philippines, and is a Filipina, but our daughter is, in these terms, a half-breed. Happily so, I'll add.
In the absence of an external pressure determining breeding, these are the only two ways I know to maintain a 'breed' - distance, or prejudice.
Horses, left in the wild, will interbreed. Indeed, my Appy is the result of an Appaloosa stallion who broke down his fence, and mated with a purebred Arabian show mare through another fence. Had the mare been a mustang, the offspring would not have been eligible for registration with the main registry of Appys. But the stallion would not have cared.
If you turned a bunch of Arabians loose in the wold, they would change with time, showing increasing variability unless there was some form of natural selection preventing some of the variability. My Arabian mare is pushing 16 hands, so I suspect one could take a group of Arabians and eventually breed into a large horse. A lot would depend on the internal genetic variability within your population, but one could certainly shift the mean.
As I understand it - and I am not a breeder of anything - the Appy registry argued to allow solid colors based on the solid colors retaining the ability genetically to sire Appy colors. I don't agree with that, since I think you should breed toward a goal. I tend to prefer performance goals for dogs and horses, but I understand those who include colors as well.
If indeed the Nez Perce had a rigorous breeding program - and I don't doubt you - then they were acting as a registry. They had specific goals, and only included those horses for breeding that would help them reach those goals.
A registry merely states what its goal in breeding is, and then includes those horses bred for that purpose, with the idea that constantly breeding them will reduce the genetic variability and increase the chance of a given crossing meeting the breed standard.
Thus the largest registry of Border Collies has refused to set an appearance standard, since they maintain the only real test of a Border Collie is performance. I think they still allow registry on merit, although I'm not certain. I know they used to do so.
The AKC has entered into a competition with them, trying to turn Border Collies into dogs that look a certain way. Conflicting goals, so they should be different breeds. I know many Border Collie breeders call the AKC version "Barbie Collies".
IMHO. In any case, I thank you for the discussion and for your insights into what is happening in the Appaloosa world.