Some Brazilian genome background from fellow Unz Review blogger Razib Khan. First, from 2011:

The Pith: Brazil is often portrayed as the second largest black nation in the world, after Nigeria. But it turns out that the majority of the ancestors for non-white Brazilians are European. …

…my post showing that Argentina is not quite as European a country as it likes to consider itself is regularly cited in online arguments … But last week in PLoS ONE a paper looking at the patterns of ancestry in the Brazilian population came to a somewhat inverse conclusion as to the self-conception or perception of the preponderant racial identity of that nation. Let me quote from the conclusion of the paper:

Among the actions of the State in the sphere of race relations are initiatives aimed at strengthening racial identity, especially “Black identity” encompassing the sum of those self-categorized as Brown or Black in the censuses and government surveys. … Nevertheless, our data presented here do not support such contention, since they show that, for instance, non-White individuals in the North, Northeast and Southeast have predominantly European ancestry and differing proportions of African and Amerindian ancestry.

The idea that Brazil is majority non-white, that is black, is one I’ve seen elsewhere. Using the American model of hypodescent, where children inherit the racial status of their most stigmatized ancestral component, no matter its magnitude, well over half of Brazilians are “black.” On the other hand, there’s the persistent trend in the recent analyses which show that black Brazilians have a much higher load of European ancestry than black Americans, while white Brazilians have a much higher load of Amerindian and African, than white Americans.

In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of six million Europeans to Brazil in the 19th and 20th centuries – a phenomenon described and intended as the “whitening of Brazil” – is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories.

Another aspect is Brazil was a much more common destination of the trans-Atlantic slave trade than the United States. Brazil was much closer to Africa, so the cost of transport and the losses enroute were lower. Plus, the Brazilian sugar economy tended to work slaves to death rapidly. Sugar was a terrible business. Among American slaves, the hierarchy of desirable jobs went something like house or skilled craft slave, tobacco (which involved a lot of semi-skilled indoor sedentary work such as rolling cigars), cotton, and finally sugar. (That’s why Jim, the runaway slave, in Huckleberry Finn is terrified of being caught and “sold down the river” to the sugar plantations of Louisiana.)

So, Brazil isn’t anywhere near as black relative to the U.S. as their respective shares of the Atlantic slave trade would suggest to the naive. Similarly, the long-running Arab slave trade out of East Africa has left a more modest genetic footprint, due to working slaves to death and castration. (It would also be interesting to know about the genetic footprint left by the sizable Islamic trans-Mediterranean slave trade, but this topic of former great interest among Europeans, such as Mozart’s opera Abduction from the Seraglio, isn’t talked about much these days, since historic examples of whites being victimized are considered in poor taste.)

… Nevertheless, after 10 years of these sorts of papers I am convinced that there really does seem to be a fair amount of admixture in the Brazilian population across color lines.

To get a sense of national patterns the authors report that a 2008 survey indicated that of Brazilians 48.4% identified as white, 43.8% as brown, 6.8% as black, 0.6% as yellow, and 0.3% indigenous. These are social constructs. In fact, it seems likely that the indigenous genetic contribution to the total Brazilian population is actually 10-15%, relatively evenly distributed across the white, black, and brown categories. Additionally, American sociologists have generally observed that while very light-skinned individuals with some African ancestry self-identify as black in the USA, in Brazil the same individuals would probably identify as white. That’s a function of the differences between North American and Brazilian societies.

Something that’s going on here is the Two Sisters Effect, which works differently in Brazil than in traditional U.S.. Say that two fraternal twin sisters are born of one parent who is pure black and one who is pure white. One sister is relatively fair in coloration, the other relatively dark. In the traditional U.S. under the One Drop Rule, both would be considered black, although the fairer sister might be invited to join the Jack and Jill Club and other black elite social institutions for those who can pass Paper Bag Test.

In Brazil, however, where there was a Color Contiuum rather than a Color Line, the fair sister is more likely to marry up the social ladder toward the whiter part of society while the darker sister is likely to marry down the social ladder toward the darker part of society. But the rest of their genes besides those affecting coloration are likely to be fairly randomly distributed according to their mutual ancestry.

So, over many generations under this kind of selection, there will be more differentiation between genes for coloration/looks and genes for everything else in Brazil than in the U.S.

Razib points out a paper noting that steamship-era Mediterranean immigrants to Brazil tended to be mostly male, who presumably tended to attract Brazilian wives (at least among those who stayed), who were likely of racially mixed backgrounds:

First, of 1,222,282 immigrants from all origins that arrived in the Port of Santos in the period 1908–1936 the sex ratio (males/females) was 1.76…Second. the two most abundant immigrants, Portuguese and Italians, had sex ratios of 2.12 and 1.83, respectively.

It would be interesting to see a comparison of Italian immigrants to America and Brazil in this regard.

More recently, Razib cites a 2014 abstract:

The Brazilian EPIGEN Initiative: admixture, history and epidemiology at high resolution

Eduardo Tarazona-Santos, et al

As part of the largest Latin-American genomic initiative, we studied three Brazilian longitudinal populational cohorts: Salvador-Bahia (n=1309), Bambui (n=1442) and Pelotas (n=3736) from Northeast, Southeast and Southern Brazil respectively. … While Amerindian ancestry was low (5-7% at population level, with no individual with > 30% of this ancestry), the three populations showed individuals with all possible combinations of African and European ancestry. At population level, African ancestry ranged from 14-15% in Pelotas and Bambui to 51% in Salvador. Our unprecedented high-resolution analysis of population structure of Brazilians in a worldwide context shows that European and African contributions differ from African-Americans at subcontinental level, due to a Mediterranean component and to the African origins of immigrants that in Brazil include Mozambique and Angola (not included in current genomic initiatives).