Intergroup conflict was commoner in prehistoric societies than in historic ones

Evidence

Because intergroup conflict seems to have been much more common in prehistoric societies than in historic societies (Bamforth, 1994; Ember, Daly, & Wilson, 1978; Keeley, 1996; Wrangham & Peterson, 1996), women most likely faced considerably greater threat of sexual assault from out-group than from in-group males, if one corrects for the amount of time spent in the proximity of both categories of males. — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 1193

Categorization

• QUESTION: The comparative-warfare claim is contested (cf. Pinker’s declining-violence thesis on the historic side); worth chasing the Keeley citations which argue for constant prehistoric warfare.
• corroborated: 2 independent passages support this claim — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 1193