Income and Mating Patterns

Robert Wright in The Moral Animal, a popular presentation of evolutionary psychology, 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 to a woman than all of another .

That 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, perhaps with the assistance of brothers and other blood relatives, a sister’s child being half as good, genetically speaking, as a child of your own. 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. The long term strategy implies a preference for good fathers behaviorally, the short term for good fathers genetically.

In a very poor society, the short term strategy is not viable because a woman cannot afford to bring up a child without the assistance of its father: It’s long term or nothing. So we would expect that rising incomes would be associated with an increasing number of women choosing the short term strategy. That, allowing for substantial time lags in social institutions, might help explain the large changes in observed behavior in developed societies over the past seventy years or so.

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 parents 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.

Both Wright’s analysis and mine treat polygyny as a consumption decision by the husband, hence more likely in the rich, but Edward Lane in The Modern Egyptians, an account of Egyptian life in the early nineteenth century, reports that:

Polygamy, … is more rare among the higher and middle classes than it is among the lower orders; and it is not very common among the latter. A poor man may indulge himself with two or more wives, each of whom may be able, by some art or occupation, nearly to provide her own subsistence; but most persons of the middle and higher orders are deterred from doing so by the consideration of the expense and discomfort which they would incur. … I believe that not more than one husband among twenty has two wives.

Lane’s “higher classes” probably did not include the very rich, who on other evidence had multiple wives and concubines, but his report suggests the possibility of polygamy not as a consumption activity but as a firm structure, with three or more adults sharing a household. That fits the pattern of the only polygamous (polyamorous) household I have observed, with multiple adults sharing the work of running and supporting a household and rearing children. The Oneida commune in the 19^th century was a much larger version of that pattern with several hundred members all married to each other. A commenter on a post on my old blog cited an article about the poorest poor in Bombay that said that men who work street sweeping there frequently join in pairs to support a woman because they do not have enough money to support a woman on their own. An arguably superior version is fraternal polyandry, practiced in Tibet and some other resource poor societies. Having the two (or more) husbands be brothers is a partial solution to the problem of men wanting to spend their resources on their own children since a child of the shared wife by one husband is a nephew or niece of the others.

In a modern society the combination of contraception and paternity testing would provide a different solution to that problem; some modern polyamories are polyandrous.

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