The warlords, satraps, and barons of ancient times visited cruel burdens upon the underclass, but there was a natural limit to what they could do. Though a man could be treated like a dog, in the end a man was a man, and a dog was a dog.
We are entering an age in which, if the line of development is not broken, our rulers will not recognize natural limits to what they can do. Viewing nature as an unnatural obstacle, they will set themselves against it. If they can treat a man more like a dog by stitching a few dog genes into him, they will try to do it, and say they are improving the human stock.