Does caucasoid mixture in nonwhites increase IQ?

For years, white supremacists and pro-race theorists have put forth the theory that white or "Caucasoid" mixture increases IQs, therefore implying that select levels of caucasoid mixture increase the potential to successful. Although no study has ever been put forth to prove this point, there was a study done which debunks this notion, read:

The claim has often been made that an admixture of Caucasoid genes actually causes an increased I.Q. in American blacks, as of Caucasoids were a homogeneous group possessing the same gene combinations, regardless of whether northern or southern, eastern or western European in origin. Such statements on admixture and I.Q. are unfounded; data do not exist to support such a contention that intelligence varies with degree of ancestry. In fact, there is no connection between test performance of an individual and the number of that person's European ancestors.

Human Variation: Races, Types, and Ethnic Groups
Second Edition
Stephen Molnar
pgs 188-189