It is a mutually beneficial relationship. The productive ones can breed (and we encourage this), and we eat most of them. We give them all of the reproductive success that they need to produce more chickens, and then we eat most of them. They reproduce more in captivity, and have a much larger population, than they ever would in the wild - even though we eat most of them.
Are there wild chickens? Not being facetious, just curious. I don't mean chicken-like birds, I mean wild chickens.
However, from what I've learned about chickens over the years (breeding them in fact) there's really only one species ~ but the wild progenitor lives in South America. The "wild chickens" in Africa are simply domesticated chickens that have "reverted to the wild", kind of like Arkansas razorbacks.
I think the reason "they" decided there were two species of chickens is that otherwise, if there were only one, and it originated in the Americas, that would mean there had to have been pre-Columbian contact, but with the Indians discovering Africa.
I suspect in the long run this question will be resolved to the satisfaction of everybody, as well as the chickens.