Three broad hypotheses

A Harvard Crimson article negative to Summers summarizes his "working lunch" talk this way: 

[[ Summers suggested three “broad hypotheses” may account for the dearth of women in science and engineering. “One is what I would call the...high-powered job hypothesis,” Summers said. “The second is what I would call different availability of aptitude at the high end, and the third is what I would call different socialization and patterns of discrimination in a search.” “And in my own view, their importance probably ranks in exactly the order that I just described,” he added. 

http://www.thecrimson.com/article.aspx?ref=505787   ]]