Us vs. Them is not in our genes (or brains), but in ourselves
In The Chronicle Review, On the perennial subject "us vs. them," while noting significant recent books, Carlin Romano offers us "Good News From the Ancients!" (January 23, 2011):
Rethinking the Other in Antiquity, by Erich S. Gruen, out this month from Princeton University Press, like all excellent scholarship massages the mind in useful new directions. Gruen, a Berkeley professor emeritus of history and classics, wields his command of ancient sources to shake a widely shared historical belief—that ancient Greeks and Romans exuded condescension and hostility toward what European intellectuals call the "Other." For those Greeks and Romans, that largely meant peoples such as the Persians, Egyptians, and Jews. Even if Gruen doesn't wholly convince on every ground that Greeks and Romans operated like Obamas in togas, regularly reaching out to potential enemies, his careful readings of Aeschylus, Herodotus, Tacitus, and others introduce us to a kinder, gentler ancient world. His analysis confirms how even back then, tossing people into a category and then hating them en masse was a choice, not an evolutionary necessity.Yes, it is a mental construct: Me better, you worse, as Carlin puts it - or in the version more familiar to me: Me Tarzan, you wrong.
Defensive claims of superiority pop up again and again through history, not because there is a "gene" or neural circuit for it but because the circumstances that excite the temptation keep reappearing, and all you need after that is a human brain, period.
Thus, when we hear that "they have found the brain area for prejudice," we would most wisely interpret as follows: "This is a brain area that prejudice may activate in some individuals."