It seems that there are 3 types of people answering question on StackOverflow:

1) People genuinely wishing to share their knowledge

2) People that are chasing gamified elements of the reputation system

3) People that belong somewhere between #1 & #2

I dont see anything that prevents any demographic from participating as long as fall into one of these 3 categories. And i dont see how being of a particular gender or race or ethnicity precludes one from sharing their knowledge on StackOverflow