A new paper in PLoS ONE, Evaluation of Group Genetic Ancestry of Populations from Philadelphia and Dakar in the Context of Sex-Biased Admixture in the Americas, doesn't add much to what we know. They looked at a several hundred individuals who are self-identified as African American and European American, as well as 49 Senegalese from Dakar. Additionally, they reanalyzed data from Latin America from whites and blacks in Brazil, as well as a group of mixed Cubans. They found what you might expect to find, African and Native ancestry shows a female bias, European ancestry shows a male bias. But Figure 3 is nice in that it illustrates how exceptional European Americans are: they are a New World population with very little admixture, that is, a "pure race." The data on people of white identification in most of Latin America, including in the European dominated southern cone, is that a non-trivial load of non-European genes exists in these populations (often indigenous ancestry down the maternal lineage). Similarly, African origin populations in the New World are invariably known to be admixed, more or less. Finally, even the "indigenous" generally show non-trivial European or African ancestry (this is evident in the regular notations of African or European ancestry being used to explain anomalous results).*
Citation: Stefflova K, Dulik MC, Pai AA, Walker AH, Zeigler-Johnson CM, et al. 2009 Evaluation of Group Genetic Ancestry of Populations from Philadelphia and Dakar in the Context of Sex-Biased Admixture in the Americas. PLoS ONE 4(11): e7842. doi:10.1371/journal.pone.0007842 * Some escaped African slaves "went native" and assimilated into indigenous tribes. The symbiotic relationship between the Seminoles of Florida and escaped blacks is well known, but not exceptional. The case in the United States is exceptional in its magnitude in that most people of native self-identifications are mixed.