The Birth of the Mestizo in New Spain

Marshall presents an excellent, albeit old, explanation of the early development of two entirely new human phenotypes: the Mestizo and the less known Zambo. Why did this happen? How does the phenomenon of miscegenation explain contemporary American views that Mexicans are a race rather than a political identification? One might consider the question, are Americans a race? What, in your opinion, complicates the concept of a national race?