Race, Genetic Ancestry, and Health: A Direction for Anthropological Genetics in the 2010′s?





Social and cultural factors are better predictors of blood pressure in African Americans more than genetic ancestry

The association between genetic ancestry and skin color has been well demonstrated (see here).  The heritability of skin color is quite high suggesting that contribution of genetic components to skin color is high as well.  Many genetic research projects support this showing that variants in pigmentation candidate genes are associated with skin color or other pigmentation traits (reviewed here).  However, it is often difficult to demonstrate the association between genetic ancestry and common diseases because social-cultural factors (socio-economic status, education, income, employment status, access to health care, etc.) confound the relationship.

The association between skin color and blood pressure among African Americans has been investigated by many researchers (see here), but more recently researchers started using genetic ancestry estimates to test the association between African ancestry and blood pressure.  In genetic studies, information on only clinically relevant variables are collected, so association between genetic ancestry and disease phenotype (here blood pressure) is often tested without adjusting for socio-cultural and environmental factors.  Only a few studies conducted so far examined 1) effects of genetic ancestry and socio-cultural factors simultaneously and 2) interactions of these factors.

Non et al. (2012) explored the association between genetic ancestry and blood pressure and between education and blood pressure using publically available Family Blood Pressure Program (FBPP) study data.  They found that education, not genetic ancestry, was significantly associated with blood pressure in African Americans and interaction between education and race also plays a role in the racial difference in blood pressure.

First, they examined if African ancestry estimated using 294 autosomal STR was a predictor of blood pressure in African Americans.  They did not observe significant difference in African ancestry between hypertensive and non-hypertensive African Americans.  In the linear regression model, education was significantly associated with blood pressure but African ancestry was not.  They did not observe interaction between African ancestry and education either.

Second, they examined if education explains difference in blood pressure between African Americans and European Americans.  African Americans with high-school degree or who did not complete high-school degree have significantly higher blood pressure than people with higher educations.  They did not observe the same pattern in European American, however.  In the regression analysis, they observed the interaction between education and race.  In addition, they showed that decline in SBP is sharper with increasing educational levels in African Americans than in European Americans.

This is an interesting study to show that education (and probably poverty), not genetic ancestry, is a very important factor affecting blood pressure in African American, suggesting that obtaining higher education will benefit African Americans more than European Americans.  As noted by the authors, one of the limitations of this study is that education was only social-environmental factor available in the dataset and they used it as a proxy for socio-economic status and other social environmental factors.  While I agree that education can be very useful for capturing the many social-environmental factors and their analyses clearly show that socio-environmental factors measured with education are very important predictors or risk factors of blood pressure in African Americans, African American societies are too diverse and heterogeneous, and there should be many socio-environmental factors that affect blood pressure but not captured with education.  They also could explore more what socio-economic factors were captured with education.

It is interesting to note that anthropologically trained scientists are showing that socio-cultural factors are as important as genetic factors assessed with genetic ancestry estimates and skin color.  In other papers, Gravlee at al. (2005 and 2009) have shown that skin color or genetic ancestry is associated with blood pressure in Puerto Ricans, but social classification based on skin color is associated with blood pressure in Puerto Ricans.  They also observed statistically significant interaction between skin color and socio-economic status.


Gravlee, C. C., W. W. Dressler, et al. (2005). “Skin Color, social classification, and blood pressure in Southeastern Puerto Rico.” Am J Public Health 95(12): 2191-2197.

Gravlee, C. C., A. L. Non, et al. (2009). “Genetic ancestry, social classification, and racial inequalities in blood pressure in Southeastern Puerto Rico.” PLoS ONE 4(9): e6821.

Non, A. L., C. C. Gravlee, et al. (2012). “Education, genetic ancestry, and blood pressure in African Americans and Whites.” Am J Public Health 102(8): 1559-1565.


Is skin color associated with blood pressure in African Americans?

Anthropologists have been interested in evolution of skin color for a long time, but I believe that anthropologists and other scientists should study about it for many reasons.  Here is one of many reasons.

Boyle (1970) and others observed association between skin color and high blood pressure among African Americans long time ago, and in these studies, skin color was used as a proxy for admixture and Africa ancestry.  However, subsequent studies demonstrated complex relationship between skin color, socioeconomic status, and blood pressure.

For example, Klag et al. (1991) observed the association between skin color and blood pressure in African Americans, and they showed that darker-skinned African Americans tend to have increased blood pressure.  They also show that this association depends on the socioeconomic status.  Among African Americans in the lowest socioeconomic status, darker-skinned African Americans had considerably higher blood pressure level than lighter-skinned African Americans, but they did not observe the same pattern among the African Americans in the higher socioeconomic status.  In their multivariate regression analysis, they observed significant interaction between skin color and socioeconomic status associated only with diastolic blood pressure.  Moreover, they showed that whether African Americans completed high school education or not had a significant effect on blood pressure and again they observed statistically significant interaction between skin color and education (please note that survey data was collected between 1972-1974).

More recent study by Sweet et al. (2007) reported similar findings.  They also found that darker-skinned African Americans have higher blood pressure in the CARDIA study, and they found the significant interaction between skin color and income.  In a similar study of blood pressure, Gravlee at al. (2005) have shown that skin color is not associated with blood pressure in Puerto Ricans, but social classification based on skin color is associated with blood pressure in Puerto Ricans.

These studies show that both genetic/biological factors and socio-environmental factors have a great impact on blood pressure in African Americans.  The effects of both of these factors on blood pressure, and maybe on other disease phenotypes, should be examined simultaneously.


Boyle, E., Jr. (1970). “Biological patterns in hypertension by race, sex, body weight, and skin color.” JAMA: The Journal of the American Medical Association 213(10): 1637-1643.


Klag, M. J., P. K. Whelton, et al. (1991). “The association of skin color with blood pressure in us blacks with low socioeconomic status.” JAMA 265(5): 599-602.

Sweet, E., T. W. McDade, et al. (2007). “Relationships between skin color, income, and blood pressure among African Americans in the CARDIA study.” Am J Public Health 97(12): 2253-2259.





























112(4): 387-399.







Genetic evidence of Indian Ocean slave trade from Indian Siddis









A support for vitamin D hypothesis of skin color evolution?: a correlation between African genetic ancestry and blood vitamin D concentration

Signorello, L. B., S. M. Williams, et al. (2010). “Blood Vitamin D Levels in Relation to Genetic Estimation of African Ancestry.” Cancer Epidemiology Biomarkers & Prevention 19(9): 2325-2331.

Anthropologists have been hypothesizing the evolutionary relationship between skin color and  vitamin D (reviews are here and here), but the mechanism of evolution has not been explained well.  Lately, I have been reading about genetic determinants of vitamin D concentration in the blood and implication for health, especially among African Americans.  In this post, I am reviewing an interesting article investigating the relationship between genes and serum vitamin D level.

Signorello et al. (2010) investigated if the differences in vitamin D concentration in the blood between African Americans and European Americans are influenced by genetic variation by examining the correlation between serum vitamin D and estimated African ancestry, and they demonstrated that serum vitamin D concentration was inversely correlated with genetic estimation of West African Ancestry.  They recruited 379 African Americans and 379 European Americans from 12 southeastern U.S. states.  They used 300 ancestry informative markers (AIMs) and estimated African and European ancestry using STRUCTURE.

They found that the estimated west African ancestry among European Americans was low ranging from 0.001 to 0.171 (mean, 0.009) (note there is no genetically pure European).  The estimated west African ancestry varied more among African Americans ranging from 0.505 to 0.999 (mean, 0.929).  Serum vitamin D concentration was lower for the African Americans than European Americans, and the lowest in the African Americans with higher estimation of west African ancestry, even after adjusting for age, sex, average daily dietary intake of vitamin D, mean residential UV radiation score, BMI, employment, smoking, alcohol intake, and education level.

This study does not show if any particular genes are involved influencing the serum vitamin D level.  However, they used the genetic ancestry, not skin color or self-identified racial identity, as a proxy for underlying genetic background, and they demonstrated that there should be genetic basis for the differences in serum vitamin D level between African Americans and Europeans Americans.  From an anthropological and evolutionary perspective, it is important to address the relationship between vitamin D level and skin pigmentation considering underlying genetic factors, but they did not investigate the relationship or they did not use skin color measurement to statistically adjust the serum vitamin D concentration.


I have been thinking about how these kinds of genetic research, examining the correlation between African genetic ancestry estimates and phenotypes (including disease related traits), should be done.  One of the major issues seems to be combining African Americans and European Americans in the same analysis.  African ancestry estimates among the African Americans tend to range widely with high estimates, while European Americans have very low African ancestry and do not have much variation.  If the distribution of African ancestry estimates is shown on the graph, there should be two non-overlapping peaks, one wide peak for African Americans and one narrow peak for European Americans.  Implication of uneven distributions in these analyses has not been discussed in this article or other similar articles.

Persistence of racial thinking in the online communities

There are arguments on Afrocentrism, Eurocentrism, and criticisms against these ethnocentrisms in the online communities, such as blogs and YouTube.  For example, some argue whether ancient Egyptians were black Africans or not, while others question if the first Europeans looked more like modern Africans or not.  Despite anthropologists, geneticists, and educators’ efforts to eradicate racial thinking among the public, I believe that these arguments exist because of persistence of racial, or typological thinking among the human population geneticists as well as the public.

Keita and Kittles (1997) argue that racial thinking, not racist thinking, persists in the studies of human evolution through use of phylogenetic trees to show evolutionary relationship of human groups and by estimating divergence time between major racial groups(e.g. Cavalli-Sforza et al., 1994; Nei and Roychoudhury, 1993).  Weiss and Long (2009) also argue that some human geneticists have replaced ‘old racial classification’ with more sophisticated scientific methods identifying human population clusters using multilocus genetic data and Structure-like population genetics methods (e.g. Rosenberg et al., 2002; Li et al., 2008). 

One underlying assumption that racial thinking and clustering approach is based on is relative reproductive isolation because of lack of gene flow (e.g., Andreasen, 2004; Cavalli-Sforza et al., 1994; Risch et al., 2002).  People, including human geneticists, with racial thinking believe that human populations have had very limited gene flow, where there are geographic barriers and linguistic, cultural, and political differences.  They also focus on biological, genetic, linguistic, and cultural differences between different groups, while assuming that there are genetic, cultural, and linguistic similarities within a human group.

However, many anthropologists and human geneticists believe that gene flow between different human groups is common and there are great biological, genetic, cultural, and linguistic variations even within small human populations (e.g., American Association of Physical Anthropologists statement on race; Livingston, 1962; Tishkoff et al., 2009).  Therefore, the clusters that human geneticists identified should not be equated with racial groups. 

So, where did the ideas of Black Africans, Europeans, Asians…. come from?  These ideas were developed based on stereotypes of people living in different parts of the world, probably very recently, after the colonial era (American Anthropological Association statement on race).  Ancient Egyptians and the first Europeans probably did not have self-identities as Africans, Caucasians, or Europeans.  Ancient Egypt was multi-ethnic state. 

Note: This also posted on the blog section of AnthroGenetics website.


American Anthropological Association Statement on Race

American Association of Physical Anthropologists – AAPA Statement on Biological Aspects of Race

Andreasen, R. O. (2004). “The cladistic race concept: a defense.” Biology and Philosophy 19: 425-442.

Cavalli-Sforza, L. L., R. Menozzi, et al. (1994). The History and Geography of Human Genes. Princeton, NJ, Princeton University Press.

Keita, S. O. Y. and R. A. Kittles (1997). “The persistence of racial thinking and the myth of racial divergence.” American Anthropologist 99: 534-544.

Li, J. Z., D. M. Absher, et al. (2008). “Worldwide Human Relationships Inferred from Genome-Wide Patterns of Variation.” Science 319(5866): 1100-1104.

Livingstone, F. B. (1962). “On the non-existence of human races.” Current Anthropology 3: 279-281.

Nei, M. and A. K. Roychoudhury (1993). “Evolutionary relationships of human populations on a global scale.” Molecular Biology and Evolution 10(5): 927-943.

Risch, N., E. Burchard, et al. (2002). “Categorization of humans in biomedical research: genes, race and disease.” Genome Biology 3(7): comment2007.2001-2007.2012.

Rosenberg, N. A., J. K. Pritchard, et al. (2002). “Genetic Structure of Human Populations.” Science 298(5602): 2381-2385.

Tishkoff, S. A., F. A. Reed, et al. (2009). “The Genetic Structure and History of Africans and African Americans.” Science 324(5930): 1035-1044.
