Hi!There are several reasons for this. The most important of them is the increase in proportion of women with the passage of time. Demographic surveys have proved that in the coming years, every country of the world will be overloaded with women. Polygamy is to keep maximum number of women within the routine social fabric. Secondly, Medical science says that hormones responsible for sexual desire are twenty percent more secreted in males than females. Implies that a male has same level of hormones after three to four days of previous intercourse. While females are different in behaviour. Some have the same desire after one month and some after many months. In case of pregnancy, a muslim mother cannot fulfill desire of his husband for almost three years. She has to deliver the child, feed him for two years and to take care of him, all day and night. From medical point of view, her body cannot afford frequent sex in such circumstances.Male sex hormones create aggression, if this aggression is not soothed thruough proper channel, it starts finding other outlets. Males become irritant and aggressive and less pateint in matters of every day life. This creates problems , sometimes leading to separation. However, there are strict rules to observe polygamy. Husbands have to treat all wives equally in all routine matters. If they fail to do so, they will have to face severe punishment here and hereafter. Polygamy, if observed following the theme behind it, is the only solution to get rid of sex marktes and exploitation centres.