I like Tyler Cowen's theory: "[the two variables are] income inequality, and the willingness of wealthier men to marry beautiful women from the lower income and

I like Tyler Cowen's theory: "[the two variables are] income inequality, and the willingness of wealthier men to marry beautiful women from the lower income and social classes. Women then compete for lucrative marriage prizes." http://www.marginalrevolution.com/marginalrevolution/2006/11/a_simple_theory.html http://www.marginalrevolution.com/marginalrevolution/2006/11... NYC has both variables.