Why are there so few women in philosophy? (again!)

The powerpoint (you-tube-ized) from my talk a couple of days ago is here.  I presupposed a picture of female attrition that I'm now less sure of.  Based on this graph from "Gender and Philosophical Intuition" (Buckwalter and Stich), I assumed women are less attracted to philosophy classes starting very early on.

 
Then there's also attrition after the undergraduate course series. You see it on