Picture an armed conflict between two tribes. What happened to the men and what happened to the women? The men from each tribe fought each other and the losing side of males were killed, often along with their children. The women, however, were kept for mating purposes. Women who pledged eternal allegiance to her tribe, the “I would rather die than sleep with the enemy”-types, were killed. So women developed a certain willingness to (sometimes reluctantly, other times not) mate with the men who killed their husbands, fathers and brothers. This happens even today.
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