monogamy is evolutionarily advantageous

formation of monogamy ensures diversity in the human gene pool.

my reasoning is as follows.
a human male in the case of reproduction is in the position of choice because females are limited by pregnancy. given the freedom, a human male will spread his sperms as far as possible, which is the seen today as the animcal instinct, and have multiple children concurrently. females however will have the burden of waiting for one child to come before having another. without monogamy, only the strongest and smartest guys get laid. soon the human gene pool will be filled with the traits of a small fraction of males. therefore the species would be less adaptive towards the changing environment.

when monogamy is enforced through cultural and social structures, however, a great many more guys can get laid due to removal of monopoly.

this also explains another problem that i have been thinking about for a long time. that is, why humans have evolved to wear clothes. by covering up the private parts, humans are less aroused sesually when they meet the opposite sex. on one hand, this may shift our attention to more "constructive" activities such as the development of civilization, which will benefit the survival of the species. (although i do not see how we could have known this before we created civilization). on the other hand, this could also be a by-product of the desire to keep monogamy, so that each person is only aroused by his or her partners in designated situations. and therefore benefit the species.

there might be a nother reason for clothing. maybe it acts like a dam, so that a human only conducts sexual acts when they meet the most desirable partner. this is because?