Who Benefits from Polygymous Marriage?

Here are some questions and suggested answers about marriage and polygyny that occur to me as I am writing lectures. 

First: What is marriage? 

I answer that marriage is a reciprocal exchange between one or more males and one or more females in which the female(s) offer the male(s) the opportunity to mate in exchange for the promise of investment in her offspring. 

I note that this is not restricted to the human species.  The pied flycatcher, a frequently adulterous English bird, exemplifies the system rather perfectly.  Adultery, of course, is what happens when one of the parties is tempted to cheat.  Males cheat by accepting the mating opportunity and then refusing to invest.  Females cheat by encouraging the male to invest in offspring that are not his own.  I also note that this excludes harem species to the extent that the male invests little or nothing in his offspring. 

It also excludes same sex marriage among humans, but I suggest that this may have no political or moral implications.  If same sex marriage is not really marriage, it is an extension of marital institutions to cover a very new kind of association.  That has to be judged according to its merits and I am, for what it’s worth, in favor of legal same sex marriage.

Second: what kind of marriage systems are there?

Three are logically possible:

1.       Monogamy (one male, one female),

2.      Polygyny (one male, more than one female), and

3.      Polyandry (one female, more than one male).

Monogamy is the most common in every human society, I suspect.  Most men (and apparently all male pied flycatchers) can only afford one wife and family.  Polygyny is also very common wherever some males do bring home enough bacon to support additional wives and kids.  Polygyny is thus, obviously, dependent upon social stratification. 

Third: why is polyandry so rare? 

There seem to be only one or two cases.  The reason seems obvious: if some number of females successfully monopolizes more than one male, then an equivalent number of females will be without mates.  Since more mates for a female does not mean more offspring, polyandry will reduce the reproductive potential of a society that practices it.  That will necessarily make it a bad option for most human societies. 

Fourth: who benefits from polygyny?

I find this question to be very interesting in so far as it is susceptible to logical analysis.  I am confining myself here to the logic of Darwinian strategies, so no one should think that I am making a case for polygyny in modern societies.  I am also making the cost/benefit analysis against the case of a society where all the marriages are monogamous.  Here is my list of winners in order of benefit:

1.       High status males

2.      All females who marry high status males (relative to those who marry monogamously)

3.      Each additional wife (relative to previous wives of the same husband)

4.      Woman who marry monogamously

Here are the losers, in order of loss:

1.       Males who are denied mates

2.      Males who marry monogamously

3.      Each wife relative to the next wife with the same husband. 

It’s pretty clear why high status males are the big winners.  They get as many wives and offspring as their status, substance, and stamina can afford.  Some men can be very big winners from a Darwinian point of view. 

Females do not benefit to a similar degree; however, in a polyandrous system, all the females get to marry up.  Consider a system in which there are fifty males and fifty females, ranked from one to fifty according to how competitive they would be in a free marriage market.  If each male is allowed three wives, then females one, two, and three all get to marry Prince Charming.  Females four, five and six get Prince Charming’s slightly less charming brother.  In this scenario, all the females get to marry up and the benefits get bigger as you go down the list of marriageable ladies.  In a larger system, where some females must settle for one husband, they still benefit.  Since the higher status males are soaking up the supply of wives, the remaining women will have a surplus of males to choose from. 

Of course, if females and males are roughly equal in numbers in the marriage market, for every male who gets three wives there will be two guys who have to go without.  Those are the big losers in the polygynous market.  Males who marry monogamously will have to pick their wives from the supply of females who didn’t rank even as a third wife for some fortunate aristocrat. 

Finally, there is the intra-familial conflict between multiple wives.  Cinderella does not benefit from the system, as she has to share Prince Charming and his resources with wives two and three.  Wives down the line benefit from marrying up, but wives one pay a cost for wives two and three in each case.  Tales of polygynous marriages almost always present the conflict between the older wife and the new girl in the harem. 

From a Darwinian point of view, most women benefit from polygyny and most men do not.  That hardly makes a case for polygyny even for women in modern times.  Polygyny requires a large degree of social stratification, which is one reason that it has been largely abandoned in modern societies along with those Downton Abbey houses.  This does explain a lot of the drama that is based on polygynous marriages a lot better than Freud ever explained anything.  Just sayin’.