Ooh! I love chicken history!
I would recommend reading Why Did the Chicken Cross the World. It’s so good, I read it twice!
Chickens were found in America since the first settlers.
Also, Polynesians introduced chickens to South America even before Columbus arrived.
Most “breeds” before Columbus were more like landraces, so they didn’t breed super consistently, but they had enough in common to be considered “breeds”. There are a few that were actually selectively bred for consistency.
By commonplace do you mean in Europe or America or worldwide?
The most common breeds were probably the various gamefowl types. These were selected to fight, so of course they had similar characteristics. The other breeds were more localized. Most chickens were just barnyard mutts.
Most, but not all breeds that existed in the west pre-Shanghai fowl were light breeds.
Dorkings, Hamburgs, Lakenvelders, Dominiques, Leghorns, Minorcas, White Faced Spanish, Buttercups, La Fleche, Polish (more or less, but with smaller crests), Campines, Braekels, Nankins, d’Anvers… and many more that I don’t feel like naming.
And of course in the east, they had more game fowl breeds, Silkies, Shanghai fowl, and many ornamental Japanese longtails and Chabos (Japanese bantams.)
We’re not using wacko methods to keep them from breeding true. Mongrels are the default. To create Orpingtons, William Cook crossed breeds with desired traits, then selected birds with all the traits he desired combined and inbred them, so they would all look the same and have the same great qualities.
And we still do it today. Ameraucanas are just Easter Eggers that were bred to be homozygous for pea combs, blue eggs, beards, slate legs, and to have certain colors and body types.
Breeds are created through inbreeding, which is a good thing, because without selection pressure, how would you get highly productive or aesthetic birds?
So many of the older breeds were produced from related birds. Maybe some birds were better fighters, or were better egg layers, or better able to escape predators, or faster growers, or just more attractive. Farmers would of course keep these ones, and hatch from them, deliberately or because more fertile, tougher birds were what were making babies. The only thing is, from one farmer to the next you might have related birds of the same “breed” because they got them from each other, but someone could easily go another way because of what he wanted or dumb luck.
But with the advent of the hen craze and poultry shows, people bred birds to similar standards. If more than two people were breeding birds that performed and looked in the same way, you could get a breed.
Okay, meat and egg “hybrids” are different though. They come from two “pure” inbred (inbreeding leads to homozygosity) families that are super unrelated that are crossed together. The offspring from this first generation will be super consistent because they are almost perfectly heterozygous for either side, but the next generation will be any mixture of either side.
