Why do men get twice the inheritance as females?

According to the Qur'anic verses below, male members inherit double what counterpart females inherit. Is this unfair?
"Allah instructs you concerning your children: for the male, what is equal to the share of two females..." (4:11)
"Allah gives you a ruling concerning one having neither descendants nor ascendants [as heirs]. If a man dies, leaving no child but [only] a sister, she will have half of what he left. And he inherits from her if she [dies and] has no child. But if there are two sisters [or more], they will have two-thirds of what he left. If there are both brothers and sisters, the male will have the share of two females." (4:176)