Polygamy

In societies where rich men are much richer than poor men, women (and their children) are better off sharing the few wealthy men; one-half, one-quarter, or even one-tenth of a wealthy man is still better than an entire poor man. As George Bernard Shaw puts it, "The maternal instinct leads a woman to prefer a tenth share in a first-rate man to the exclusive possession of a third-rate one."

(Psychology Today: Ten Politically Incorrect Truths About Human Nature)

In some instances concubines had wider latitude to act in their own interests than they might have had in poor marriages. An Icelandic folk saying of uncertain age goes, "Better a good man's frilla [a kind of concubine] than married badly."

(Jesse Byock: Viking Age Iceland)

Since some icelanders had more than one woman, others must have felt very cold indeed, alone in bed during those icy icelandic nights. The disadvantages of polygamy for non-elite males should be evident to anyone who was taught New Math at school:

Non-injective and non-surjective: BAD (unless you are lucky A, that is)

Bijective: kind of OK for everybody I guess. Surely better than this.