The mobile nuclear family has throughout history coexisted with the polygamous type. Even in the Western part of the world, where monogamy has long been at least the nominal rule, some people have set up polygamous families more or less openly …

If monogamous societies have always included informal polygamy, the technical polygamous societies – which make up fully three fourths of the world – have been largely monogamous.

Robert Wernick
The Family (Human Behavior), p. 35
Time-Life Books, 1974