"Because men, compared to male chimps, have such relatively small testicles (large testicles indicate a species where many males mate, one after the other, with the same female), we might guess that promiscuous societies were uncommon in the immediate human past."

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Actually, there is a sense in which polygynous marriage has not been the historical norm - even where polygyny is permitted, multiple wives are generally reserved for a relatively few men who can afford them or qualify via formal rank. For eons and eons, most marriages have been monogamous, even though most societies haven't been

— Robert Wright