I feel that the above two write-ups make very valid and interesting points. Gender roles are reinforced by society and creates a chicken or the egg situation: a never-ending loop of gender behavior imperatives creating themselves. However there are a few important questions that I feel have been left out.
First off, neither touched on the biology of the brain. These gender characteristics must have originally come from somewhere. The brains of men and women are wired differently. According to Brainplace.com men have 4% more brain cells than women. This is not to say that men are necessarily smarter because next the site says that the connections between the brain cells are better in women. Language is the dominant hemisphere in men but women have more access to both sides, it may be why women are said to be better multi-taskers. But the most relevant info to this write up comes in the study of the limbic system. Differences here give women advantages and disadvantages. The limbic part of the brain in women is larger which makes them more in touch with their feelings and better able to bond emotionally with others (which suggests why women the world over are primary caretakers for children). But the disadvantage is they are more susceptible to depression. Even with this fact, though, men kill themselves more often and by more violent means. Conclusion: women are more emotional and men are more aggressive, generally speaking. These things are not taught, it's biology. So these biological differences are the roots of these reinforced gender behaviors. Maybe there's not as much reinforcement as is suggested above. Perhaps these things like boys like to play with trucks and girls like to play with dolls were originally driven by biology and are self-perpetuating in that sense.
Second off, I wonder what would happen if you took a bunch of female and male babies and put them on a desert island and they are taken care of by adults who purposely reinforce any gender roles as little as possible, and then the children are left to their own devices once they can adequately feed and care for themselves? The real goal of the experiment would be to see if there's a new genesis of gender roles, which might prove that boys will be boys and girls will be girls anyway. And then they will go on to "reinforce" those behaviors to the children those little horn dogs will invariably have.
Oh, and one more thing: as to the discussion that gender really isn't binary, it is obvious that it is not since there are individuals born with both sex organs. However, the small percentage of them does make them anomalies and doesn't necessarily mean that human beings are supposed to or are meant to have multiple genders. So I feel I can freely discuss the differences between males and females above as I did without mention of them. But of course, as is the case with anybody with any kind of difference from the norm like homosexuals and transsexuals, they deserve the same respect and dignity as everybody else and it does anger me when doctors so freely think they can play God and decide what gender these children will be. It downright infuriates me when penises are removed just because they are small, but, hey, I may be biased there being that I am a man, and, as such, am thankful I have the little guy down there.