There is no definite evidence to show when Patriarchy originated, or whether it was present even before Homo sapiens were evolved. Many other animals including many of the non-human primates exhibit patriarchy. But many other species of both primates and non-primates do not exhibit patriarchy. This shows that as different species evolved differently they adhered to different systems regarding Gender relations.
As per evolutionary anthropology there is a natural selection of behaviour which gives the species maximum survival benefit.
In case of early Homo sapiens specialisation into a section who hunt and a section which do not hunt but only gather food is an important change from rest of primates which helped in its survival. The human baby needed adult care and support for a long time compared to other species. This meant many of the women were not available for going out to hunt. Also the increased physical strength exhibited by males might have been more suitable for hunting. Thus hunting more or less became the domain of males while child rearing and gathering the domain of females.
Many believe that compared to most other species humans exhibit the strongest male to male bonding. This might have been the result of group hunting of large animals several times the size of humans. At the same time humans show the least female to female bonding. May be the way of life of a gatherer might have been to see a competition in every one else.
As the hunter-gatherer society evolved, incest taboo that prevents sexual act between close relatives resulted in females going out to join other groups. Many of the non human primates shows same behaviour,though in some others it is the males who go out of the parental group.
Why women went out and not men? Is this again because of the strong male to male bonding in humans?
In most of the primates where females go out of their parental group (chimpanzees,hamadrayas baboons), patriarchy is very strong. One reason for this is it is difficult for the new-comer female to make any sort of bonding with females of her adopted group.
In contrast in some species, females remain in their birth communities their whole lives. Here females form alliances against aggressive males. Vervet monkeys macaques, olive baboons, patas and rhesus monkeys are examples for this ‘female bonding’ . Thus in these species the males behave with much more respect towards females.
As human society developed from hunter-gatherer system to cultivation and feudalism patriarchy became stronger. Surplus wealth created had to be transferred to off springs. But if it had to be given to girls who go out of the house in marriage also,it meant diluting of the family wealth. So a male only inheritance was developed for the survival advantage of the family as a unit but at a distinct disadvantage to females.
Why females agreed to this? By then men had almost complete control over tools for production of wealth like land,agricultural implements, weapons,domestic animals etc. It was also men who went out to wage war to capture more land and slave labourers.Women might have perceived that their interests is best served through alliances with men, not with other women.
Feudalism was slowly replaced by Capitalism due to the scientific revolution and advent of mass production of goods. Joint families got disbanded as they could not survive the new economic system. Women who were small scale producers of goods with in the joint family system became either confined to household work or had to go out to work in factories. As production became more and more mechanised the importance of physical strength in production diminished. But still women who did the same work as men were under paid by the Capitalists. Thus even though Capitalism helped in reducing gender discrimination by allowing women to sell their labour in the market, it was at a lower wage and the unpaid house work and child rearing still remained the sole responsibility of women. When ever family needed more of her unpaid work, she had to sacrifice her paid work.
Change in economic system to Capitalism also resulted in change in political system. More and more Nation states were formed and monarchies were replaced by democratic system of governance. Initially only the rich men were able to contest or even vote. Great struggles by working classes and women forced the ruling capitalists to allow universal franchise. Legislators passed many gender sensitive laws.
Thus now in most of the countries legally there is not much gender discrimination. Even there are positive discrimination for women in many ways. But still women are discriminated widely in the society though much less than before.
Study of animals shows us that female to female alliances and alliance with like minded oppressed males are important in creating more egalitarian societies.
Let us hope that such an alliance of oppressed classes can create not only a gender-equitable but also a social-equitable society in near future.