"The widening of income in equality is caused mainly by technological changes leading to closer ties between education and employment. The crash happened because the attempt to turn America into an ownership society failed. Americans will own a house and in turn use the house as collateral to borrow money to invest."
This is from
which I saw just a few minutes ago. To my mind it ties in perfectly with what Herrnstein and Murray said about the emergence of a cognitive elite. In a low-tech society, one didn't need a lot of education (except perhaps as an apprentice in a medieval guild) to get and hold a job. It's very different here and now.