[ROYMANgo]

I always thought that the "one drop rule" was due to the dynamic adaptive nature of white supremacist systems, which depending on population demographics and other factors could adapt its definition of white. In societies where "real" whites were outnumbered and needed support from "mixed" classes, white could have an inclusive definition, including the mixed descendants. In societies, like anglo-America, where such a compromise wasn't necessary, a stringently exclusive definition of whiteness could be applied. Just a theory, I'm sure it's full of holes.