One of the established rules in Islamic Legislation is that man generally has the right to inherit what equals the share of two women enjoying the same degree of relativity to the one who bequeathed. However, there are some cases in which man and woman share equal inheritance rights and sometimes she may exceed him.
Islam has estimated man's twofold share of inheritance counting on the fact that he is the one to be responsible for all the expenses, while woman has nothing to do with this matter. He is to cover his expenses as well as the needs of his wife, his children, and everyone he is held responsible for, while woman is financially secured by her father and brother before getting married. She may spend from her own money to sustain herself before getting married, but after marriage, all her expenses and needs fall under the responsibility of her husband and her own money is devoted only to fulfill her own needs. Therefore, it is fair enough for a man to inherit twice as much as woman in order to enable him to undertake the responsibilities and duties he shoulders towards his family.
Such a distinction in inheritance has nothing to do with gender, but it is ascribed to the status of the inheritor, the extent of his needs, and the burdens laid on his shoulders. There are many cases in which a man inherits as much as a woman; for instance, both parents inherit one-sixth of their dead son's legacy, when he leaves a son. Moreover, in certain cases of inheritance a woman's share may be more than that of a man.
With respect to the superiority of males over females pertaining to the case in which children inherit from one of their parents, Allah, the All Wise Legislator, has considered the conditions of the inheritor and the extent of his needs. Undoubtedly, the needs of a son and his responsibilities in life are far greater than those of his sister, for he is charged with sustaining himself, paying the dowry of his wife, covering the expenses of his sister and children, and sustaining his poor parents, whereas a girl – during her life – is not obligated to spend a penny on such matters.
On the other hand, the Great Legislator has taken into consideration the kind of relation that ties the inheritor and the one to whom he bequeaths pertaining to the case in which both the mother and father inherit the same share from their deceased son's legacy. This is because the son is responsible for sustaining them equally during his life in case of being well-off and the father is poor and unable to earn his livelihood. Thus, justice dictates that the father and mother should have an equal share in their son's property upon his death.