With the men I know in my life, if THEY were responsible for having babies, the first time they had a period the pain and inconvenience would have them running to the nearest surgeon to have a complete hysterectomy... so the human race would have died out decades ago.
Women have periods so they can make room a baby, after they get there first period it happens around 4 days evey month and once a woman stops having periods they cant have another baby and do you really want to bleed 4 days every month?
its really not fair. i think guys dont have periods because they cant take on the pain of cramps every month. men can most be described as weak. women have to have periods every month while guys get to be jolly and dandy . in conclusion GUYS CAN'T HANDLE THE PAIN!