“In the January 2012 issue of the Philosophical Transactions of the Royal Society, three West Coast scholars – Joseph Henrich of the University of British Columbia, Robert Boyd of UCLA, and Peter Richerson of UC Davis – published an article entitled “The Puzzle of Monogamous Marriage.” The authors point to the following paradox:
The anthropological record indicates that approximately 85 per cent of human societies have permitted men to have more than wife (polygamous marriage), and both empirical and evolutionary considerations suggest that large absolute differences in wealth should favour more polygamous marriages.
Yet, monogamous marriage has spread across Europe, and more recently across the globe, even as absolute wealth and differences have expanded. Here, we develop and explore the hypothesis that the norms and institutions that compose the modern package of monogamous marriage have been favoured by cultural evolution because of their group-beneficial effects – promoting success in inter-group competition. In suppressing intrasexual competition and reducing the size of the pool of unmarried men, normative monogamy reduces crime rates, including rape, murder, assault, robbery and fraud, as well as decreasing personal abuses.
By assuaging the competition for younger brides, normative monogamy decreases (i) the spousal age gap, (ii) from seeking wives to paternal investment, normative monogamy increases savings, child investment and economic productivity. . . Polygamous societies engage in more warfare.
Quoted from William Tucker’s Marriage and Civilization (Regnery Publishing: 2014), pp. 87-88.