Supply and demand, yes. But polygamy?
I live in a place where polygamy is allowed, but generally avoided. One of my friends has two wives. When asked why, he once quipped “more suppliers means more competition and better service for the customer”. Now I know, both intuitively and through observation, that people with two wives seldom lead “peaceful” lives. As an economist, how would you explain that?
Your friend is demonstrating the truth of the old saying that the only thing more dangerous than an economist is an amateur economist. He’s right that ex post he potentially enjoys the benefits of competition, but he neglects the question of ex ante bargaining.
The truth is that most people who argue against polygamy simply cannot count. Polygamy does not create extra wives – it just changes the dynamics of who marries whom. A few rich or otherwise attractive men will marry several women each, and other women will therefore be in short supply and in a strong bargaining position. (In a patriarchal society, it will put their fathers in a strong bargaining position instead, but this is not the fault of polygamy itself.) Women get more choice: they can share a millionaire with someone else, or they can take their pick from humbler men, many of whom will never marry and each of whom, presumably, will be very eager to please.
Your friend may have found a way to enjoy his double marriage, although I wonder about that. Wise women will have insisted on binding conditions before entering into a marriage with a polygamist. Your friend must have found a way to wriggle out of these – or he’s hiding his pain. But what is certainly clear is that in reducing the supply of wives for other men, he has placed them at a serious disadvantage. I am not sure why he is still your friend at all.
Also published at ft.com.