Comment by mattm

Strictly in terms of different cultures, more cultures have polygamy than strict monogamy. If the advantage was evolutionary, you would not find so many cultures that have a degree on polygamy.

Polyandry on the other hand, is extremely rare which makes complete sense when factoring in the effort required for a woman to raise her children.

http://eclectic.ss.uci.edu/~drwhite/worldcul/Codebook4EthnoA...

  # of cultures - Maritial Composition:
  36 - Missing Data
  186 - Independent nuclear, monogamous
  453 - Independent nuclear, occasional polygyny
  69 - Preferentially sororal, cowives in same dwelling
  18 - Preferentially sororal, cowives in separate dwellings
  344 - Non-sororal, cowives in separate dwellings
  157 - Non-sororal, cowives in same dwelling
  4 - Independent polyandrous families