Question for Runners

I run fairly in the morning here in Berkeley, so (on a good morning) I often don't see anyone at all. But sometimes I see other runners. Invariably if the runner is male he will make some gesture in greeting, usually a wave. However if the runner is female, she will refuse to even make eye contact much less wave. Assuming my experience is similar to other male runners (and is not just because I look scary...) here is the question -- do female runners wave to other female runners? Is it that waving in greeting is something only male runners do or is it a separation of the sexes issues?