Well, apparently human beings brought the instinct to “enslave” weaker human beings from their animal ancestors! There is a warrior ant in amazon that can do only one thing with its jaw-kill! So to bring up its babies and do chores it does a heinous thing again and again. It raids the nests of weaker ants, kills them and steals their hatchlings, then they grow up as slaves, when these slaves grow old, they go out to raid another nest!
Scary, huh? I wont like such neighbours!