We know about men being polygamous from our ancient sources. All of our forefathers had several wives, and according to eastern tradition a man can have several wives, as many as he can support. It is quite another matter whether he benefits from it. But in reality this is our nature, and in reality this comes from the Spiritual World.
By studying the structure of the spiritual world we discover the way our spiritual prototypes were created. In the spiritual world our spiritual prototype is called Zeir Anpin (ZA) (Small Face,) and the spiritual prototype of a woman is called Malchut (Kingdom.) And they are created in such a way that there is ZA—one and only, but there are eternally many Malchut that exist. That is to say, that naturally spiritual roots define the polygamy of men.
Courtesy of http://www.youtube.com/watch?v=f1Bs9_k3kVc