Question Summary:
Why is polyandry prohibited?

Question Detail:

 
Why in Islam its primissable for med to marry 4 women but women cant marry 4 men?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
You enquire why is it permissible in Islām for a man to have four wives whereas women can only have one husband. The straight forward and simple reply is Allah permitted men to have a maximum of four wives and Allah prohibited women to have more than one husband at a time. Allah is Al-Hakeem (All Wise). Every order of Allah has wisdom in it and is best suited for the individual and time.
When we apply our limited intellect to the differences in the enquired issue, we understand that it is a well-established research and fact that males and females differ in their character and conduct based on their natural make up. Consider the following:
-A US team at the University of Pennsylvania scanned the brains of nearly 1,000 men, women, boys and girls and found striking differences. Male brains appeared to be wired front to back, with few connections bridging the two hemispheres. In females, the pathways criss-crossed between left and right. These differences might explain why men, in general, tend to be better at learning and performing a single task, like cycling or navigating, whereas women are more equipped for multitasking, say the researchers in the journal Proceedings of the National Academy of Sciences (PNAS). The same volunteers were asked to perform a series of cognitive tests, and the results appeared to support this notion.[1]
-The researchers also believe the physical differences between the two sexes in the way the brain is hardwired could play an important role in understanding why men are in general better at spatial tasks involving muscle control while women are better at verbal tasks involving memory and intuition. Psychological testing has consistently indicated a significant difference between the sexes in the ability to perform various mental tasks, with men outperforming women in some tests and women outperforming men in others. Now there seems to be a physical explanation, scientists said.
“These maps show us a stark difference - and complementarity - in the architecture of the human brain that helps to provide a potential neural basis as to why men excel at certain tasks, and women at others,” said Ragini Verma, professor of radiology at the University of Pennsylvania in Philadelphia.
Men tend to outperform women involving spatial tasks and motor skills - such as map reading - while women tend to better in memory tests, such as remembering words and faces, and social cognition tests, which try to measure empathy and “emotional intelligence”. [2]
Researchers also mention “Females and males maintain unique brain characteristics throughout life. Male brains, for instance, are about 10% larger than female brains.” Disparities in how certain brain substances are distributed may be more revealing. Notably, male brains contain about 6.5 times more gray matter -- sometimes called 'thinking matter" -- than women.[3] 
The religion of Islām is a practical religion that also considers nature in directing laws and obligations. Polyandry is impractical for a woman and will place unbearable burden upon her. Thus, the prohibition of polyandry for a woman is based on care and compassion for her.
How will a woman fulfill the marital demands of more than one man, his intimacy needs, his temperament, and various other challenges? When a woman with one husband experiences so many challenges, imagine the burden with more than one husband.
What will a woman in such a relationship do when she is pregnant with one man’s child? How will the child’s lineage stay secure? Consider the emotions, jealousy, etc. she will have to undergo from the other husbands.  
It is clear from the above that Allah Ta’ālā’s ruling of prohibiting females to have more than one husband reflects the hikmat and wisdom of Allah and His compassion for women.
And Allah Ta’āla Knows Best
AbdulMannan Nizami
Student Darul Iftaa
Chicago, IL, USA
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net