About Hijab

Hijab has not been introduced by religions and it was there at least after the invention of agriculture. According to Will Durant in The Story of Civilization, after an abrupt transition from hunting-gatherer to agricultural societies, humans learned that the possession of a land as well as plenty of farm workers would give them a sheltered life. Thus, they needed to protect their wives, the source of creation of their workers, namely their children. Consequently, the practice of polygamy which had been encouraged for both men and women before agriculture invention (again for survival), faced disapproval, obviously by men: sharing wives would led to sharing children, consequently to losing/sharing their properties. Hijab has practiced in many societies for several reasons, such as security, however, I see somehow its origin or at least one of its main sources in patriarchy.
There is also a strong correlation between wearing hijab and the social class throughout the history of civilization. Beside the price of clothes, which comes first to the mind, according to Motahhari in 'Hijab issue', this correlation origins in again patriarchy and also economic reasons. The reason that lower or middle class did not practice hijab as well as upper class was because women needed to work outside, e.g. working in a farm and interacting with other men. Exactly here I want to make a point: one of the reasons men and women are careless about hijab in modern societies is economics, because women need to work outside and earn a living. Besides, since women are not economically dependent on men, their wearings can not be controlled. Also, secure societies might be another reason. Anyway, I do not want to discuss here about how much they practically need to uncover to work outside and interact with men.
Finally, about Islamic perspective on Hijab in the form of scarf, it is clear in Quran that women need to be careful about their clothing, however, since the Quran verse about hijab, I believe, is a bit ambiguous, it is hard to fully reject the idea of scarf.