By the time that the the English came to North America the poor personal hygience of average 15th century Castillian had taken it's toll in the native population.  Not to mention that there population densities of native populations in the areas colonized by the English were far lower than in the Valley of Mexico, and elsewhere?

The relationship between pre-Columbian population density and the percentage of the present population that is mestizo holds true in the Cono Sur  (Argentina, Chile, Uruguay) as well.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg