I’ve often wondered why the Europeans adopted monogamy. Some might say this is just another example of the Enlightenment values. But that to me is ducking the question. The Enlightenment values, something about individual freedom, are not guaranteed by monogamy — patriarchy dominated in the West until very recently, and Pakistan allowed its women to vote before Switzerland did. If you’re happy to lord it over one wife, why should you shrink from lording it over a harem? So it’s not the Enlightenment that caused the West to adopt monogamy. In fact, it’s not even clear that the Enlightenment values even necessarily endorse monogamy: if a bunch of individuals want to live in a hippy commune then surely that’s their business.
I’ve also wondered why the Europeans, or Christians to be more precise, scorned consanguineous marriage (as in marrying your cousin). Christians are unique among the Semitic faiths in this regard. Jews and Muslims are generally, although by no means always, endogamous. It’s not only the Semitic-inspired societies where consanguineous marriage is practised: in South India, among some castes, marrying one’s maternal aunt/uncle is quite common.
Angus Maddison has an interesting perspective. According to him, the Church actively encouraged monogamy and non-consanguineous marriage. In a world of high infant mortality, monogamous non-consanguineous marriages would have meant fewer heirs when one died. In such situations, the Church would have stepped in and acquired the property. If you married within your clan, or had a number of wives so that the chance of a son surviving to adulthood was higher (women typically didn’t own property — yet another proof that the Enlightenment didn’t cause monogamy), the Church lost out on your property. So it was the Church acting as a despotic government that led to the Europeans adopting monogamy and rejecting consanguineous marriage. In the Muslim world, inheritance laws were clearly established early on (they are written in the Quran), so the Islamic state had little room to grab your property.
But this despotic action by the Church had interesting unintended consequences — there always are unintended consequences. Monogamy and non-consanguineous marriage led to a weakening of clan ties, leading to individualism on the one hand and loyalty to the nation state on the other. These of course shaped the rise of the West.