more than one wife,what about more than one husband ?

if more than one wife then why not more than one husband as both male and female r the same in todays life.both have the equal contribution to life.

Well... women could do that, but that would end up in utter mess. Imagine she's pregnant and she wouldnt even know who the father is :). And she has to bear that child and raise him/her. In mens case its not an issue. Besides that its not accepted in society where a woman has multiple husbands. Yet, theres no rule as such which says men can do it and women cant ;)