Theodore C. Bergstrom noted in his paper "On the Economics of Polygyny" (U. Mich. Center for Research on Economic and Social Theory, Working Paper Series 94-11 - see below) that "Although overt polygamy is rare in our own society, it is a very common mode of family organization around the world. Of 1170 societies recorded in Murdock's Ethnographic Atlas, polygyny (some men having more than one wife) is prevalent in 850. The following is for those who would enjoy a more technical paper about polygyny from a Social/Economic Scientific perspective:
http://www.econ.ucsb.edu/~tedb/Evolution/polygyny3.pdf
http://www.econ.ucsb.edu/~tedb/Evolution/polygyny3.pdf