I always thought babies were born as blank slates and the parents molded and taught them gender roles, etc. 

I had two boys. We didn't allow guns in the house. We didn't talk about them, just basically ignored their existence. The first time the oldest got some Lego blocks, he built a gun! We had plenty of toys and dolls etc, and he always went for the cars and traditionally "male" toys. We didn't encourage it, he wasn't in childcare, he was just "like that."

My best friend had two girls, the same ages. The wanted to do the girly things when they came over. 

We moved away and had two girls. Meanwhile my friend had some boys. She later called and apologized for all the things she had said about my parenting. I was amazed at how different and easier girls were. 

I have always been a women's libbist, and have a degree in chemistry. But I had to admit I was wrong about the blank slate idea. 

My second son did have a period when his sister was born when he was inseparable from his baby doll, that he dragged around by the leg.He refused to put clothes on it, so I had to crochet a little dress directly onto the doll because I didn't like her being naked all the time. 

And my older daughter insisted on climbing trees and couldn't STAND dolls. She is like me, not a girly girl at all. But the older one now has a degree in linguistics and is choosing to stay at home and raise children while her husband works. They hope to get a big horsefarm someday and work together doing tourist rides in Alaska.

Despite my women's libbist tendencies, I have LOVED being a mom and my kids are wonderful, so I must have done something right. My brother-in-law stayed home with the kids while my sister worked, and that worked for them. 

The bottom line is that boys and girls ARE overall wired differently, but there is some overlap. There will always be traditionally female and male roles, but also with some overlap. The one thing we can do to really screw up society is to have quotas. The best thing to do is to encourage each person to follow their heart.