Yesterday's news prominently featured an Israeli air strike in Gaza that killed leading Hamas militant Nizar Rayan, all four of his wives, and 9 or 10 of his 12 children. I wonder if the Muslim approval of polygyny, allowing men to have up to four wives if necessary for humanitarian reasons, may help explain why Islamic militants seem to be some of the most aggressive on the planet. I would think that, other things being equal:
• The men most prone to seek multiple wives would tend to be the assertive and even aggressive ones. (This premise intuitively makes sense, but that's all the more reason to give it careful scrutiny before making any significant bets on my reasoning here.)
• Every time a polygynist takes an additional wife, his action has a double-whammy effect on the makeup of the next generation's population: It reduces the number of women available to bear the children of more-passive men, and it increases the number of women who will bear the children of assertive ones.
• Thus, in a society that allowed multiple wives, over time we would expect more descendants of assertive men, and fewer descendants of passive ones, than we would expect in a monogamous culture.
Assuming intuitively that assertiveness is at least partially determined by heredity (another assumption requiring critical scrutiny), this gives us a clue about how a society might eventually look after X generations of polygyny.
The above analysis is pretty simplistic, of course. It doesn't take into account other factors that doubtless contribute to the hyper-aggressiveness of Islamic militants, such as overcrowding in Palestinian 'refugee camps' and the inability of many Islamic societies to generate the kind of widespread economic progress that is comparatively common in the West. (The latter may itself be due in part to a population prone to aggressiveness.) Nor does it take into account the increased likelihood that aggressive males might die violently before fathering as many children as they might have in a normal lifespan.
But I do suspect it there may be something to it.