These forces put man in a position of wanting it both ways – stable long term partners associated with producing heirs and secondary partners used outside the accepted relationship. Indeed, Scheidel asserts that the first monogamous societies (Greece and Rome) were socially imposed. By this he means there was social pressure to monogamous based on the increasing importance of cooperation among coalitions (peer groups), needed to deal with external challenges. This pressure led to a moral standard that monogamy should be the only acceptable marriage practice.
In both Greece and Rome there grew to be severe penalties for having sexual relations with someone else’s wife, but no penalties for relations with slaves or concubines.