Regarding human breeding experiments, it might be a good idea to review the Wikipedia article on eugenics.
think the edited writing prompt puts an interesting twist on it. I don’t know of any real concentrated eugenics effort that lasted for anywhere near the duration the prompt asks for.
What if some secret cult has been doing eugenics in the shadows for a thousand years, and one day we get to meet the product of that process – a being that’s supposedly human in the same way a chihuahua, a rottweiler and a St. Bernard are all supposedly the same species as a grey wolf?
Bonesaw would probably love it.