So, an economist's definition of hatred...
"is the willingness to pay a price to inflict harm on others." In laboratory settings, social scientists have observed subjects playing the "ultimatum game," in which, say, with a total kitty of $10, Player A offers to split the cash with player B. If B accepts A's offer, they divide the money accordingly, but if B rejects A's offer, both players get nothing. "In thousands of trials around the world, with different stakes, people reject offers of 30 percent [$3 in our example] or less," says Glaeser. "So typically, people offer 40 or 50 percent. But a conventional economic model would say that B should accept a split of even one cent versus $9.99, since you are still better off with a penny than nothing." (If a computer, rather than a human, does the initial split, player B is much more likely to accept an unfair split”a confirmation of research conducted by professors at the Kennedy School of Government. . .)
Clearly, the B player is willing to suffer financial loss in order to take revenge on an A player who is acting unfairly. "You don't poke around in the dark recesses of human behavior and not find vengeance," Glaeser says. "It's pretty hard to find a case of murder and not find vengeance at the root of it."
Another interesting point...
The psychological literature, he found, defines hatred as an emotional response we have to threats to our survival or reproduction. "It's related to the belief that the object of hatred has been guilty of atrocities in the past and will be guilty of them in the future," he says. "Economists have nothing to tell psychologists about why individuals hate. But group-level hatred has its own logic that always involves stories about atrocities. These stories are frequently false. As [Nazi propagandist Joseph] Goebbels said, hatred requires repetition, not truth, to be effective.
Then there is the mention of the race-based violence against black people in late 19th century...all of which was based on propoganda by rich people to avoid the spreading of wealth amongst them.
So, finally what it comes down to, in my opinion, is that the reasons are not always evolutionary or natural or a fear of being extinguished...it can also be individual greed...ok, there might be some that argue that greed is also a facet of survival, but then again, is it always the case ? I mean, is greed for everything based on the survival instinct ?