I think biologically, we can use minority exceptions if we want, but generally speaking humans are born with reproductive organs either on the inside or the outside. This is a biological fact, we are a 2 gender species. Human behaviour, hormonal levels and the roles of each gender, however, are completely different matters.
There are some exceptions in some smaller tribes, but generally speaking men have been domineering for a very long time. And I think this is mostly down to the sexual dimorphism of the human race - men are a bit larger and stronger than women. There are exceptions and lifestyle expectations that exaggerate this, but this is statistically quite true. And this was primarily so that men could hunt some deer or whatever and women could have babies in caves. Gender roles in this time were necessary for our survival, though I believe that the dominance of men was completely unnecessary in this deal for survival but happened because of this physical disadvantage women had in this time.
In the modern world, however, physical superiority is not our greatest survival trait and thanks to modern technology and lifestyles, those ancient gender roles that helped our ancestors survive are no longer any more necessary than having a coal fire in your living room.
Lots of conjecture exists today on the difference between our minds. One study claims that the average male brain has larger cerebral capacity than that of the average female brain, but this was not only unverified by further studies but also, nobody can even find and particular relevance of such a minor difference anyway. Some look at school results and claim girls are higher achievers than boys - an interesting point to make. Though this is true only of high schools; by college level there is no statistical difference in any grades or achievements. And even in high schools, the aptitude tests are no different. Which leads us to the conclusion that perhaps there is some societal difference at work here, or perhaps a poor methodology of teaching.
One can claim that the under representation of women in the science and technology industries is a sign of either poorer ability or sexism at play - but women are not only dominating certain middle graduate jobs nowadays (such as accountancy) but I've read studies that claim there to be no statistical difference between successful applications by men and women in the S&T industries, only a major difference in those applying for such courses in college, which will obviously lead to under representation in the industry. I believe this, too, is down to societal expectations in which careers are considered more "manly" or "womanly" to undertake. (Imagine a heterosexual man manicuring nails, or a woman on a construction site as examples). Perhaps this is partly down to the way people play with children and develop their abilities, that's something I also think is at least partly the case.
We also have the ideas that men are far more promiscuous and lack control of their sex drives (I'm not even going into why that's bullshit), and the idea that women are more emotional (especially in relationships). Again, I do not believe women are literally more emotional. I think boys are taught to "man up" and not cry, and to control their aggression as a strong man can seriously cause harm to an average woman, yet I believe girls are not. Many even teach each other how to cry in order to use emotional blackmail, but this is not considered immoral in any way. And it is now encouraged to be a "psycho chick" and basically don't bother to act in any way sane with a partner, whereas we men are expected to be perfectly stoic and rational in response. Basically, society teaches us emotional control and encourages emotional lack of control in women simply because it is our perfection of how it simply is.
The bottom line is - while these gender roles started due to a necessary symbiotic relationship, they are no longer necessary to us at all. We're slowly in the process of abandoning them as a society, but we are not there yet. It's going to be a while.
