" Societies that chose ‘normative monogamy’, or an insistence upon sex within exclusive marriage, tended to tame their young men, improve social cohesion, balance the sex ratio, reduce the crime rate, and encourage men to work rather than fight. This made such societies more productive and less destructive, so they tended to expand at the expense of other societies. "

― Matt Ridley , The Evolution of Everything: How New Ideas Emerge