Brazil's population derives from diverse ethnic groups
Physical characteristics associated with race - such as skin or hair colour - do not necessarily reflect a person's genetic ancestry, a new study suggests.
Our study makes clear the hazards of equating colour or race with geographical ancestry
A group of scientists - writing in the journal Proceedings of the National Academy of Sciences - have found that people who appear white may genetically be mainly African, while people who look black may genetically be European or Amerindian.
The scientists, from the University of Minas Gerais in Brazil and the University of Porto in Portugal, said their data indicated that, in Brazil, colour was a weak predictor of African ancestry.
"There is wide agreement among anthropologists and human geneticists that, from a biological standpoint, human races do not exist," said one of the researchers, Sergio Pena.
"Yet races do exist as social constructs," Dr Pena and his colleagues said.
Colour roots
The research took place in Brazil and on the island of Sao Tome, a former Portuguese colony off the African coast.
Races do exist as social constructs
Brazil's population comes from three separate ethnic groups: the original Amerindians, Europeans, and Africans.
These groups have inter-married and inter-bred, yet some Brazilians are popularly regarded as white, others as black.
The researchers found 10 gene variations that could reliably tell apart - genetically - 20 men from northern Portugal and 20 men from Sao Tome.
But the genetic differences did not have anything to do with physical characteristics such as skin or hair colour, the researchers found.
Poor guide
They next tested two groups - 173 Brazilians "classified" as white, black, or intermediate based on arm skin colour, hair colour, and nose and lip shape, and 200 men living in major metropolitan areas who classified themselves as white.
The results threw up some surprises: maternal DNA suggested that even the "white" people had about 33% of genes that were of Amerindian ancestry and 28% African - indicating that European men often fathered children with black and Indian women.
"It is interesting to note that the group of individuals classified as blacks had a very high proportion of non-African ancestry (48%)," they wrote.
"Our study makes clear the hazards of equating colour or race with geographical ancestry and using interchangeably terms such as white, Caucasian and European on one hand, and black, Negro or African on the other, as is often done in scientific and medical literature," the scientists' report said.
Mark Shriver's original study, and several subsequent studies, show that this is also true for USAmericans. For example, the correlation between degree of African admixture and skin-tone for members of the U.S. Black community is very weak. The correlation between degree of African admixture and skin-tone for White USAmericans is nonexistent. From the detailed data on this, I concluded in Afro-European Genetic Admixture in the United States that a long-term historical selection process has affected admixture ratios among the U.S. population. There was a brief but interesting discussion of this point in the African American DNA Research Forum.
Note to William: We were talking the other day about making sure that all the articles in the http://backintyme.com/admixture directory are listed in your index. Now that I think of it, we have a similar directory of journal articles just on skin tone and other "racialized" features at http://backintyme.com/skincolor. These articles are not listed in your index because they are not about admixture. Do you think we should expand your index to include them? Or do you think we should start another index just for phenotype articles? Or should we just leave it alone, since there has not been much interest around here in the heredity of physical features?
Color and genomic ancestry in Brazilians
Flavia C. Parra,* Roberto C. Amado,† José R. Lambertucci,‡ Jorge Rocha,§ Carlos M. Antunes,† and Sérgio D. J. Pena*¶
This work was undertaken to ascertain to what degree the physical appearance of a Brazilian individual was predictive of genomic African ancestry. Using a panel of 10 population-specific alleles, we assigned to each person an African ancestry index (AAI). The procedure was able to tell apart, with no overlaps, 20 males from northern Portugal from 20 males from São Tomé Island on the west coast of Africa. We also tested 10 Brazilian Amerindians and observed that their AAI values fell in the same range as the Europeans. Finally, we studied two different Brazilian population samples. The first consisted of 173 individuals from a rural Southeastern community, clinically classified according to their Color (white, black, or intermediate) with a multivariate evaluation based on skin pigmentation in the medial part of the arm, hair color and texture, and the shape of the nose and lips. In contrast to the clear-cut results with the African and European samples, our results showed large variances and extensive overlaps among the three Color categories. We next embarked on a study of 200 unrelated Brazilian white males who originated from cosmopolitan centers of the four major geographic regions of the country. The results showed AAI values intermediate between Europeans and Africans, even in southern Brazil, a region predominantly peopled by European immigrants. Our data suggest that in Brazil, at an individual level, color, as determined by physical evaluation, is a poor predictor of genomic African ancestry, estimated by molecular markers.
I wonder if Flavia Parra at the college in Minas Gerais is related to Esteban Parra, the former Shriver grad student who has done a lot of admixture work in Soutn Carolina.
Joined: 30 Mar 2005 {Posts: 1082 } Location: New Jersey
Posted: Thu 06 Apr 2006 20:49 Post subject:
Frank wrote:
Note to William: We were talking the other day about making sure that all the articles in the http://backintyme.com/admixture directory are listed in your index. Now that I think of it, we have a similar directory of journal articles just on skin tone and other "racialized" features at http://backintyme.com/skincolor. These articles are not listed in your index because they are not about admixture. Do you think we should expand your index to include them? Or do you think we should start another index just for phenotype articles? Or should we just leave it alone, since there has not been much interest around here in the heredity of physical features?
I was going to add the article on Brazilians after I'd read Zsana's post, but didn't have time today. I had read the entire article before, but had forgotten about it. I'm glad Gordon posted it. I think it would be good to add the skin-tone studies to the admixture index under a heading reading something like "Studies on Skin Tone", since in some cases the studies have to do with whether skin-tone correlates to level of genetic admixture. I have to run now, but maybe we can do this tomorrow.
'
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