Gender roles

So this video was just forwarded to me by a peer, and its quite comical but it also really got me thinking. Why are most men so manly and most girls so girly? Have you ever noticed how very little children are totally egalitarian, there is no division of toys and play time based on what sexual organ you have, kids simply play with the other kids they like. But when they start to being puberty, boys start playing with boys, playing sports, or shoot em up games, and girl start playing with other girls, doing each other hair and make up. Now this got me thinking, does this happen as a result of socialization, are boys just taught to be like boys, and girls the same, or is there some sort of biological imperative that drives us to associate with others homogeneous to us. Are the only things that drive mixed gender relationships biological urges that lead us to believe we will one day copulate with this "Friend." Its hard to say, I've done extensive research into this and all my efforts appear fruitless. The most i can conclude from empirical data is that is possible that both are correct, or that neither are correct. Personally i think it has to do with our society, we are taught by our parents, our peers essentially all external sources of influence perpetuate the cycle we seem to be stuck in. Of course its easy to say that our society is fine, women are treated equal blah blah blah, but clearly there is more to it than we really understand, but i would like to warn all the men that not everything lasts forever, so be nice to your woman before they have all the power.