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Anyone who has ever thought seriously about religion is bound to have thought about violence. It’s everywhere in our holy books: Open anyone’s bible to any random page and you’re not likely to read for very long before you stumble on some smiting, slaying, gouging, ripping apart, or something of the sort. It’s more than a stylistic choice: Bibles are manuals for moral life, and every discussion of good and evil is necessarily going to touch on that most extreme form of human behavior: violence toward another living person.

But what if we’ve understood violence all wrong? What if we’re much more likely to use violence not against those we perceive as others, strange and foreign, but against those who are most similar to us, our friends and neighbors and kin?

That’s the thrilling idea that Russell Jacoby, professor of history at the University of California, Los Angeles, entertains in his new book, Bloodlust. “Despite an ocean of words about violence—its origins, course, and prevention,” he writes, “something has gone virtually unrecognized: its primal form is fratricide.” And it begins, of course, with Cain and Abel, history’s first recorded murder. Jacoby spoke to Long Story Short host Liel Leibovitz. [Running time: 27:02]

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to Long Story Short.