How Can People Hate Other People They Don't Even Know?

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13. Hunter-gatherers first launched violent raids at least 13,400 years ago

This study from ScienceNews supports your claim. A short excerpt:

More than 8,000 years before the rise of Egyptian civilization, hunter-gatherers went on the attack in the Nile Valley.

Skeletons of adults, teens and children excavated in the 1960s at an ancient cemetery in Sudan known as Jebel Sahaba display injuries incurred in repeated skirmishes, raids or ambushes, say paleoanthropologist Isabelle Crevecoeur and her colleagues. The site, which dates to between 13,400 and 18,600 years ago, provides the oldest known evidence of regular, small-scale conflicts among human groups, says Crevecoeur, of the University of Bordeaux in France.

Although people buried at Jebel Sahaba don’t show signs of having fought in a one-time battle, they participated in an early form of sporadic warfare, the researchers conclude May 27 in Scientific Reports.

“Repeated violent episodes were probably triggered by well-recorded environmental changes” around the time people were buried at Jebel Sahaba, Crevecoeur says.

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