Income and Human Mating Patterns
1. Wright argues that monogamy tends to be associated with societies that are either very poor, so a man cannot support two families, or have fairly even income distributions, so that half of one man is almost always worth less than all of another from the woman's standpoint.
It occurs to me that the first point is also relevant to women's choice between their two alternative mating strategies, long term and short term. The long term strategy is to pair up with the most desirable man she can get and jointly produce and rear children. The short term strategy is to get pregnant by the most desirable man she can and then rear the child herself. There seems to be good evidence that both women and men are equipped for their roles in both strategies, with different preferences among potential mates according to which is being followed.
2. Wright cites anthropological evidence that dowry, payments by the bride's family to the groom, is almost always associated with socially enforced monogamy. His explanation is that without enforced monogamy, the very desirable--most obviously the wealthy--man can trade half of himself for all of a bride. If he can't do that, he trades all of himself for all of a bride plus some cash. (My summary of Wright's analysis, not his)
I think he is missing something. As I argued long ago in my Price Theory chapter on love and marriage, polygyny, by letting some men bid for more than one wife, bids up the price of a wife on the marriage market. If women own themselves the result is more favorable terms in marriage. If their husbands own them the result is higher bride price or lower dowry, since a dowry (ignoring lots of complications) is a negative bride price. Enforced monogamy lowers the price of a wife not merely to the man who would otherwise have had two wives but to all men, hence makes bride price less likely and dowry more likely.