Thursday, July 12, 2007

Income and Human Mating Patterns

I've been reading Robert Wright's The Moral Animal, which seems to be a good popular presentation of evolutionary psychology. Two points occurred to me.

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.

In a very poor society, the short term strategy is not viable because a woman cannot afford to bring up a child by herself–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 fifty years ago.

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.


Anonymous said...

Speaking of Economics and Human Mating Patterns, I thought you might be interested in this in the New York Times.
More Sex is Safer Sex: The Unconventional Wisdom of Economics
-- Dagonell (from Live Journal)

Anonymous said...

As I understood years ago Steven and David are friends.

David Friedman said...

Steve and I are friends. He sent me a copy of the book. I sent him an explanation of why I thought he failed to justify the title.

I think I'm also a character in the book.

Anonymous said...

I'm skeptical that your "short term strategy" makes sense in an evolutionary psychology sense. In human's evolutionary environment (presumably hunter gatherer bands) were women often wealthy enough to raise children on their own? I would expect that gathering enough nutrition for two people while taking care of a helpless baby would be beyond the means on a single provider.
I'd guess the strategy is less hardwired and more the result of people dynamically adapting to the opportunities available. More economic psychology than evolutionary.

Anonymous said...

"In human's evolutionary environment (presumably hunter gatherer bands) were women often wealthy enough to raise children on their own?"

Never, but the death rate among hunter-gatherers, especially males, tends to be so high that these cultures have to develop a web of relationships that ensure orphans and widows are supported. In all the cases that I can think of, this safety net would also protect "abandoned" women and children. In the more extreme matrilineal cultures in Africa, a woman's main support comes from her brothers and other male blood relatives, whether she's in a permanent relationship with a lover or not. In other hunter-gather cultures, marriage is a key organizing principle, but the deficit of surviving adult males is corrected by polygyny, and it is very rare for a fertile woman to remain unmarried or a child to remain without a father.

Possibly the high death rate makes hunter-gatherers more aware than usual of the need for carrying on their band. In addition, children, natural or adopted, are ones only chance of continuing to eat if one happens to live past the point of being able to get ones own food - and it takes several children to provide a good chance of one of them surviving. So children are generally so valued that nearly everyone is quite happy to adopt a child, related or not, and a woman with small children is more valued than a girl of unproven fertility.

A man who got a woman pregnant and declined to marry her and raise the child would usually be regarded as daft, and some other man would snap up the woman along with the child. Probably more typical for "single motherhood" is a woman whose lover died before a marriage could be arranged, or a woman left pregnant by a traveling trader or raped by raiders from another tribe. Generally, among hunter-gatherers such a woman can easily find a husband and stepfather for her child.

Primitive agricultural societies can be much different; they often grow right up to the maximum population their fields or irrigation water supply can support, and so a starving woman and children might evoke a "better them than us" reaction more often than an impulse to add another wife and more children to your household. I think such hard-heartedness has to be learned, but cultures that adapted to these conditions have ways of teaching it. There are Old Testament passages that encourage such hard-heartedness (as well as the mass murder of strangers), and other passages that limit it, e.g. the specific injunction to take care of your brother's widow. Jesus tried to ameliorate this, but both the medieval church and the sterner Protestants came up with many ways of classifying others as condemned by God...


Anonymous said...

Some years ago I read an article about the poorest poor in Bombay. The article said that men who work street sweeping there frequently join in pairs to support a woman, often lying about it ('living with my brother and his wife') because they do not have enough money to support a woman on their own. So - half a wife is better than none?

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Andy said...

"I sent him an explanation of why I thought he failed to justify the title."

Would that be the "More Sex is Safer Sex" bit, or the "Unconventional Wisdom..." bit of the title?

Anonymous said...

Prof. Friedman

Any chance of your providing a brief explanation of why Steven Landsburg failed to justify the title?

David Friedman said...

Alex asks about my criticism of the title of Steve's new book.

If you look at the analysis he offers, it involves a sexually inactive man having more sex at the expense of a sexually active man. AIDS transmission goes down--but the amount of sex doesn't go up, all that changes is who is having it.

To justify the title he would have to consider something like a case where a sexually inactive man has one more unit of sex than before and a sexually inactive (or active for that matter) woman has one more unit, with nobody having less. But in that case AIDS transmission goes up, not down.