There's an interesting study on gender differences in competitiveness in a patriarchal vs. matrilineal society ( http://management.ucsd.edu/faculty/directory/gneezy/pub/docs... )

The gist of it being that in the former males are much more competitive, and in the latter, females are. While there are of course real physiological differences between men and women, don't discount out of hand the effect culture has as well.

There don't need to be "meetings where men gather to conspire to keep women down" for a society to have a significant biasing effect.