Islamic law, as a matter of fact, deals with the issue of legislation from a real perspective that considers all the dimensions which man-made legal systems may ignore
As far as the question of “inheritance” is concerned, Allah, the Divine Law-giver, says in the Qur’an, (Allah chargeth you concerning (the provision for) your children: to the male the equivalent of the portion of two females…) (An-Nisa’ 4: 11)
Men, undoubtedly, shoulder more responsibilities than women do. As a father, husband, son, or brother, he should provide for his children, wife, mother, sister; he should strive hard to make both ends meet.
Islam, as a divine religion, does not ignore the above fact and sets down rules that strike a balance between men’s responsibilities and women’s rights.
Shedding more light in this issue, it should be stated that Islam gives the girl half of her brother’s share in inheritance because Islamic Law doesn’t oblige her to spend any money on anybody other than herself. On the other hand, Muslim man, who is usually the bread-winner of the family, is obliged to spend on his wife, his children, his brothers, his sisters, and his mother and father.
Therefore, since the financial burden is much higher on the male than the female, Islam gave the male double of his sister’s share, and in this way, Islam has given the woman a just proportion. Let’s take an example. If a father dies and leaves 30,000 dollars to his children (let’s say there are 2 sons and 2 daughters). Each son gets 10,000 dollars and each daughter gets 5,000 dollars. However, the sons have to support their mother, their wives, their children, and their sisters (if the sisters are not married yet), while the sisters can keep the money to themselves. So, who ends up having more money at the end? Of course, the girls.