Book Review: Medical Apartheid by Harriet A. Washington

On the Father’s day Sunday this year, I was at the Salem Baptist Church, south side mega church, for prostate specific antigen (PSA) screening and PSA study recruitment event.  We offered PSA screening for prostate cancer several occasions at this church and this church has an annual health event to encourage African American church members to have healthier lifestyle.  Five out of eight people who were working in the screening event that day were African Americans, including the PI of the project, who is African American male urologist at Northwestern medical school.  The first African American man who came in for PSA screening jokingly said, “Ok, I will be the first guinea pig.  What do I have to do?”

African American men have poorer health conditions compared to African American women or European American men and women, but African American men are usually underrepresented in many medical research projects, most likely due to difficulty recruiting them for medical research projects or clinical trials.  Why is it so difficult to recruit African American men?  Why do they refuse to participate in medical research?

This book, “Medical Apartheid,” illustrates the reasons why it is difficult to recruit African Americans for medical research and why they mistrust physicians or medical institutions rooted in the American history beginning the enslavement of Africans.  The author, Harriet A. Washington, illustrates history of injustice in health, not from the victors’ perspective.  The advance in medical science was achieved some way through exploitation of African Americans, but was hindered at the same time because of flaws in their research designs, scientific methods, and reasoning.

Considering the history of slavery and racial segregation, it was not surprising to read that White doctors did not treat the slaves like they would for white patients.  Slave owners, physicians’ real clients, did not want to spend much money to treat their slave, if treatment cost more than they could make a profit from their slaves.  African Americans knew that white doctors’ treatments did not work well or worsened the problems, and preferred their traditional healing methods (p.48).  Even after the slavery ended, African Americans suffered with poor health conditions because they did not have access to good health care due to low income, no health insurance, and poor living environments (p. 152).  Medical racism continued until recently, and medical procedures, such as hysterectomy, were done to African Americans and they were recruited to medical research without them fully understanding medical procedures, experiments, or research.

It was very surprising to read that a various painful and dangerous medical experiments were done to African Americans either poorly informed or without consent, without anesthesia during the slavery.  Tuskegee Syphilis Study that followed untreated African American men with syphilis over 40 years and performed autopsy for hundred subjects is well known, but there are many more.  For example, James Marion Sims, father of American gynecology, developed a surgical treatment for vesicovaginal fistula using slave women as experimental subjects (p.61-68).

Even after 1950s, medical experimentation targeted vulnerable segments of American society, low-income African Americans, prisoners, and children.  Between 1944 and 1994, nontherapeutic radiation was injected to study subjects, and African American had higher risk of being the subject of the experiments.  African Americans were targeted to experiment of biological weapon as well (p. 361-363).  Washington states that many African American subjects who went through medical experiments and African American patients who received medical procedures involuntary thought that physicians were really caring them (p. 219).  Washington further states that medical abuse is far from over and medical experimentations are still performed on people of African descent in this country as well as in Africa (p. 386-396).

Scientific racism was a major paradigm in the 19th century in the U.S. and Europe to show that African Americans and African as inferior subspecies of human.  Scientists and physicians tried to show scientifically that there are anatomical and physiological differences, such brain size, immune system, and skin color, and the body of African Americans were displayed in St. Louis World’s Fair in 1906, a zoo in New York City, and a saloon in New York City transformed into an operation room, to prove that African Americans and Africans were inferior.

Washington sees the contradictions.  Even though White physicians believed that African Americans were physically different from European Americans, African Americans were treated as a ‘clinical material’ in medical schools for instruction and experiment (p.106-108).  Unnecessary surgeries were performed to demonstrate clinical procedure to the medical students.  After death, their bodies were used for dissection, even in Georgia where anatomical dissection was illegal until 1887 and in northern states, using stolen bodies from graves (p.120).  Northern states imported African American bodies for dissection from southern states (p.123).

Today, clinical trial is one way to receive the best treatment available, especial for the people with an advanced disease condition and traditional established treatment methods failed to cure or improve their health.  However, African Africans are more likely to be recruited for high risk clinical trials for a newly developed HIV drag or an implantation of artificial heart than European Americans, but poor minority populations are less likely to be able to receive the expensive treatments after they are developed.  African Americans who have been subjected to experiments as a ‘clinical material’ may see clinical trial differently.  Washington quotes the Richmond Daily Dispatch published in 1854 saying that African Americans believed if they entered medical school hospital, they would not come out alive (p.108).

Having read this book, it is understandable if African Americans do not want to participate in clinical trial or medical research.  African American patients are feeling anxious about their medical conditions, when they come to a clinic in a hospital, an institutions that have similar social structure as in slavery.  Many physicians, high-rank nurses and administrative stuffs are European Americans, while lower-rank hospital stuffs are minorities.  Some hospital and medical school buildings have architectural styles and motives that symbolize the power of European civilization.

Embodiment of social inequality causes health disparities

Krieger, N. 2012 Methods for scientific study of discrimination and health: An ecosocial approach. American Journal of Public Health 102(5):936-945.

In this paper, Krieger explains how discrimination based on racial/ethnic origins affects health of the racial/ethnic minorities.  She uses a bio-cultural approach to understand the interactions between social aspects (social structure, economic and social derivation, individual’s life-long experience of racism, and individuals’ cognitive aspects) and biological aspects of race (physical traits and exposures to toxins, hazards, and pathogens).  This approach incorporates the temporal (life-cycles starting in utero to the end of life) and spatial (from individual to global level) aspects that affect minority health.  While incorporating the wide variety of aspects of minority individuals and societies into her theoretical framework, she focuses on the causal relationship between discrimination and health, so she sees health inequality is manifestation of social inequality.

But we really need to look at these tables from her paper to understand the social context.

Table 1 Analyzing US Racial/Ethnic Health Inequities in Context

There are more African Americans living at poverty level, unemployed, and without health insurance compared to European Americans.  Infant mortality rate is much higher among African Americans, and more African American self-report having poor health status.  Minority groups are underrepresented in the congress and state legislature.

Table 3 Postelection National Poll Results for Statement on Racial Discrimination, November 3-7, 2010

However, so many white Americans and Tea Party and Republicans agree that “Today discrimination against Whites has become as big a problem as discrimination against Blacks and other minorities.”

The core concept in her approach is embodiment of social inequality.  I believe the concept of embodiment came from habitus, idea developed by Pierre Bourdieu, a French social theorist who also talked about social capital.  Embodiment is one of the core aspects of habitus, and I believe it means that people’s e experience, material word, and social structure are incorporated deep into one’s cognition.  Krieger develops this concept further to reflect biological aspects related to health inequality.  Because of discrimination, racial minorities are more likely to be exposed toxins, hazards, and pathogens and surfer from economic and social deprivation and inadequate medical care, so racial minorities are more likely to have worse health condition.

I believe embodiment is the concept that we should explore in our research and could be very useful to analyze social determinants of health.  For example, we can use this idea to analyze the relationship between fast food culture and health.  In the U.S. fast food restaurants are fun place for kids and provide quick and inexpensive food for teenagers and adults.  It is culturally acceptable to go to fast food restaurant regularly, if you do not have time and money.  The food tastes good for kids and fills adults’ stomach for a long time.  Over time, we develop the taste for fast food, and going to fast food restaurant became an integrated part of people’s life and cognition.  People who grow up with fast food restaurants now have children and take them there regularly.  It is not surprising if these children prefer French fries over vegetables.  Because of targeted marketing and economic condition, low-income individuals, and many of them are racial/ethnic minorities, are more likely to be exposed to these high fat high calories diet.

While she focuses on racial discrimination as one of the causes of health inequality, her ecosocial approach seems to be a holistic framework for analysis of social determinants of health.  Human and our societies are very complex, we need a framework as holistic as possible to capture multidimensional aspects of human societies (social determinants of health, racism, etc.) and human biology (health).

Because her focus in this paper was explaining the causal relationship between discrimination and health, she did not explain how this framework can be used to reduce health inequality.  If we can identify the social issue related to racism and health that we hope to fix, how can we use this approach to develop a strategies for intervention?

Why I am interested in genetic epidemiological study of prostate cancer: Is prostate cancer disparities due to gene or environment?

Prostate cancer is the most common cancer among men in the U.S., and African American men have 63% higher incidence compared to European American men.  Prostate cancer incident rate was 228.8 cases per 100,000 in African American men from 2005 to 2009, while the incidence rate was 140.3 per 100,000 in European American men (DeSantis et al. 2013).  Globally, African descent men have high incidence and mortality (Rebbeck et al. 2013), and incidence of prostate cancer is rising in African countries.  Only established risk factors for prostate cancer are age, family history, and race/ethnicity, and the cause for disparities in prostate cancer incidence is still not well understood.

Environmental and social/cultural factors may play roles for increasing prostate cancer risk among African descent men, but the causal relationship of any environmental and social/cultural factors with prostate cancer risk is not well demonstrated.  Many suggest that diet likely plays roles for Pca risk.  For example, differences in serum vitamin D levels between African Americans and European Americans have been well demonstrated, and some suggested that differences in vitamin D levels may explain prostate cancer disparities.  However, epidemiological studies, mainly conducted in people of European descent, show inconsistent results.

Access to health care, socioeconomic status, neighborhood derivation, and other socio-cultural factors affect stage and tumor grade at the diagnosis, treatment choice, and mortality, but these factors may not explain the difference in prostate cancer incidence.

On the other hand, there is strong evidence for genetic factors that explain increased incidence in African Americans.  Admixture mapping identified loci at 8q24 region showing association between African genetic ancestry and prostate cancer risk (Freedman et al. 2006).  Admixture mapping takes advantage of long-range linkage disequilibrium (LD) in recently admixed populations such as African Americans and Hispanic Americans, and with use of ancestry informative markers (AIMs) that have large allele frequency differences between ancestral populations, fewer number of markers is required to capture genomic variation than genome wide association study (GWAS).  This approach is powerful, when the prevalence of disease is different between two populations and used to identify genomic region that are associated with many diseases that have different prevalence between populations (Batai and Kittles 2013).  Association of 8q24 variants with prostate cancer has been replicated in African Americans, Caribbeans, and West Africans.  In addition, GWAS among African American identified a novel locus at 17q21 associated with Pca (Haiman et al. 2011).

GWAS among European and Asian populations identified number of prostate cancer susceptibility loci, but the replication of GWAS identified loci in AA has been difficult (Batai et al. 2012), and we have a lot of work ahead of us to understand how genetic factors affect prostate cancer risk in African American men

References:

Batai K, and Kittles RA. 2013. Race, Genetic Ancestry, and Health. Race Social Problems 5:81-87.

Batai K, Shah E, Murphy AB, Newsome J, Ruden M, Ahaghotu C, and Kittles RA. 2012. Fine-Mapping of IL16 Gene and Prostate Cancer Risk in African Americans. Cancer Epidemiology Biomarkers & Prevention 21(11):2059-2068.

DeSantis C, Naishadham D, and Jemal A. 2013. Cancer statistics for African Americans, 2013. CA: A Cancer Journal for Clinicians 63(3):151-166.

Freedman ML, Haiman CA, Patterson N, McDonald GJ, Tandon A, Waliszewska A, Penney K, Steen RG, Ardlie K, John EM et al. . 2006. Admixture mapping identifies 8q24 as a prostate cancer risk locus in African-American men. Proceedings of the National Academy of Sciences 103(38):14068-14073.

Haiman CA, Chen GK, Blot WJ, Strom SS, Berndt SI, Kittles RA, Rybicki BA, Isaacs WB, Ingles SA, Stanford JL et al. . 2011. Genome-wide association study of prostate cancer in men of African ancestry identifies a susceptibility locus at 17q21. Nature Genetics 43(6):570-573.

Rebbeck TR, Devesa SS, Chang B-L, Bunker CH, Cheng I, Cooney K, Eeles R, Fernandez P, Giri VN, Gueye SM et al. . 2013. Global Patterns of Prostate Cancer Incidence, Aggressiveness, and Mortality in Men of African Descent. Prostate Cancer 2013:12.

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

Batai, K. and R. A. Kittles (2013). “Race, Genetic Ancestry, and Health.” Race and Social Problems 5(2): 81-87.

In June 2013 edition of Race and Social Problems journal, we published this review article.  I think, for anthropologists who have a training in genetics, it is an interesting direction that we should explore more.  When I was almost done with my dissertation work, I began to think what I could do after I got my degree.  I was dissatisfied with anthropological genetics.  Although I was excited to investigate human genetic variation and evolution and had fun learning and teaching (I am still interesting in these topic and continue to explore), I felt “so what?”  I understand the importance of understanding migration history and genetic variation in the world, but I felt that anthropologists and many people, mostly wealthy people, are interested in human past and variation mostly only for their intellectual interests.  Who really care about our findings?  Are they really useful knowledge?

Then, I began thinking about using anthropological perspectives and methods to help other people.  I contacted my current mentor, Dr. Rick Kittles, to see if I could do genetic research on health disparities.  I learnt genetic epidemiology, a study of roles of genetics in determining or influencing disease risk in families or populations.  In the genetic epidemiology, a lot of population genetics knowledge and methods are applied to the basic epidemiological research design.  More recently, genetic epidemiologists are showing interests in gene and environment interactions.  Here, environment refers to lifestyle and socio-cultural factors.  Gene and environmental interactions is basically what anthropologists call “bio-cultural perspective,” but genetic epidemiologists think more statistically.

In the U.S., we see a great racial health disparities.  Differences in access to health care and health screen can explain a part of health disparities, but there are more complex, genetic, biological, and socio-cultural factors that are intertwined with ‘race.’  Anthropologists are trained to understand this complex relationship.  We can bring different insights in the genetic research of health disparities from scientists who were trained in other fields, and we can contribute to biomedical science in unique ways.

Genes associated with human pigmentation traits in Genome-Wide Association Studies (GWAS)

Although there are many issues, Genome-Wide association study (GWAS) has been a powerful method to identify genetic variants associated with phenotypic traits.  GWAS is generally used to find genetic variants associated with disease, but it also found variants associated with anthropometric traits, such as height and BMI.  Also, there are several GWAS mainly among people of European descents aiming to find genetic variants associated with pigmentation characteristics (hair, eye, and skin color, freckles, and skin sensitivity to sun or tanning ability) (e.g., Eriksson, 2010; Han, 2008; Kayser, 2008; Liu, 2010; Nan, 2009; Sulem, 2008; Sulem, 2007)   These GWAS identified variants associated with pigmentation characteristics on SLC45A2 (Chr5), IRF4 (Chr6), TYRP1 (Chr9), TYR (Chr11), KITLG (Chr12), SLC24A4 (Chr14), OCA2/HERC2 (Chr15), MC1R (Chr16), and ASIP (Chr20).  These studies showed very strong association of variants in these genes with hair color, eye color, freckles, sensitivity to the sun, and tanning ability.

However, because the skin color does not vary much in European populations, these GWAS were not very successful showing the association between genetic variants and skin pigmentation, and only one of these studies, in which people of non-European descents were included, successfully showed the association between skin color and an IRF4 variant (Han et al. 2008).

Another GWAS among South Asians demonstrated the association of skin color with variants in two genes (SLC45A2 and TYR), but the study also found that another gene, SLC24A5 (Chr15) is associated with skin color (Stokowski et al. 2007).  The association of SLC24A5 variants with skin color in African Americans has been reported previously (Lamason et al. 2005).  More recently, Kenny et al. report that an amino acid change in TYRP1 associated with blond hair among Solomon Islanders (Kenny, 2012).

Identifying these genetic variants is important not only to understand major human phenotypic variation and the mechanism of evolution of pigmentation traits, but also to find variants that may be associated with skin cancer and to understand the risk factors for vitamin D deficiency.  Because of admixture, African Americans exhibit a great range of skin color, so they are desirable for genetic study of skin pigmentation.

Eriksson, N., J. M. Macpherson, et al. (2010). “Web-Based, Participant-Driven Studies Yield Novel Genetic Associations for Common Traits.” PLoS Genet 6(6): e1000993.

Han, J., P. Kraft, et al. (2008). “A Genome-Wide Association Study Identifies Novel Alleles Associated with Hair Color and Skin Pigmentation.” PLoS Genet 4(5): e1000074.

Kayser, M., F. Liu, et al. (2008). “Three Genome-wide Association Studies and a Linkage Analysis Identify HERC2 as a Human Iris Color Gene.” American Journal of Human Genetics 82(2): 411-423

Kenny, E. E., N. J. Timpson, et al. (2012). “Melanesian Blond Hair Is Caused by an Amino Acid Change in TYRP1.” Science (New York, N.Y.) 336(6081): 554.

Lamason, R. L., M. A. Mohideen, et al. (2005). “SLC24A5, a putative cation exchanger, affects pigmentation in zebrafish and humans.” Science (New York, N.Y.) 310(5755): 1782-1786.

Liu, F., A. Wollstein, et al. (2010). “Digital Quantification of Human Eye Color Highlights Genetic Association of Three New Loci.” PLoS Genet 6(5): e1000934.

Nan, H., P. Kraft, et al. (2009). “Genome-Wide Association Study of Tanning Phenotype in a Population of European Ancestry.” J Invest Dermatol 129(9): 2250-2257.

Stokowski, R. P., P. V. K. Pant, et al. (2007). “A Genomewide Association Study of Skin Pigmentation in a South Asian Population.” American Journal of Human Genetics 81(6): 1119-1132.

Sulem, P., D. F. Gudbjartsson, et al. (2008). “Two newly identified genetic determinants of pigmentation in Europeans.” Nat Genet 40(7): 835-837.

Sulem, P., D. F. Gudbjartsson, et al. (2007). “Genetic determinants of hair, eye and skin pigmentation in Europeans.” Nat Genet 39(12): 1443-1452.

TYR and OCA2: two genes associated with skin pigmentation in African Americans

Shriver, M. D., E. J. Parra, et al. (2003). “Skin pigmentation, biogeographical ancestry and admixture mapping.” Human Genetics 112(4): 387-399.

Previously, I wrote about correlation between West African Ancestry (WAA) estimates and skin color among African Americans and African Caribbeans (here).  They used 33 ancestry informative markers (AIMs) that have large frequency differences between African and European populations.  Three of these markers are candidate genes for skin pigmentation (TYR, OCA2, and MC1R), so they examined, if these skin color candidate genes are associated with skin color (Melanin Index measure using the DermaSpectrometer).

Two pigmentation candidate genes (TYR and OCA2) and many other AIMs were associated with M Index without adjusting for WAA.  When they adjust for WAA, only TYR remained significant.  Then, they used ADMIXMAP, admixture mapping software, to find segments of genome that are associated with skin pigmentation because of the differences in their genetic ancestry.  In this analysis, TYR and OCA2 are associated with skin color, but not MC1R.

Their analyses demonstrated that two pigmentation candidate genes (TYR and OCA2) likely to cause differences in skin color between African and European populations.  TYR produces an enzyme, tyrosinase, which catalyzes the first two reactions in the melanin synthesis pathway.  Mutations in OCA2, or P gene, cause the common type of albinism.

I hope to review follow-up research projects later to further understand genes involved in production of dark skin in African and African American populations.

Geneticists tend to overemphasize the importance of genetic factors for resolving the ethnic health disparities

Sankar, P., M. K. Cho, et al. (2004). “Genetic Research and Health Disparities.” JAMA: The Journal of the American Medical Association 291(24): 2985-2989.

We (geneticists, media, students, etc) tend to focus on the genetic aspects of research and overemphasize on the importance o f genes on human evolution, health, etc.  As an anthropologist, I tried to be careful about it and I tried to consider socio-cultural aspects as well, but I admit that I often focus on genetic aspects more than socio-cultural aspects.  In this article, Shankar et al (2004) argue that overemphasizing genetic factors in ethnic health disparities research can have negative impacts.

Although they are well aware of many factors causing ethnic health disparities, researchers tend to overemphasize the potential benefits of their genetic research resolving the health disparities problems.  One of the reasons why geneticists overemphasize on genetic factor is their funding.  U.S. National Human Genome Research Institute (NHGRI) took an initiative to address the health disparities.  The negative consequence is that the attention shifts away from real social-cultural problems that need to addressed, but are difficult to fix, such as poverty, unequal access to health care, diet, etc.  Also, overemphasizing genetic factors may reinforce the racial rebelling and stereotyping.

It is true when we write grant proposals and papers, we have to say that our findings from genetic research can uniquely contribute to resolve the existing problems.  We do not mean to overemphasize, but it is important to note that research findings can be very important.  In addition, we scientists loose objectivity and tend to thick findings from our research project is so special.

The correlation and variability of African genetic ancestry and skin color among African Americans

Parra, E. J., R. A. Kittles, et al. (2004). “Implications of correlations between skin color and genetic ancestry for biomedical research.” Nature Genetics 36: S54-S60.

Shriver, M. D., E. J. Parra, et al. (2003). “Skin pigmentation, biogeographical ancestry and admixture mapping.” Human
Genetics
112(4): 387-399.

 

These articles are getting little old, but their findings are interesting and important.  They examined the correlation between skin pigmentation and estimated African ancestry.  Using a DermaSpectrometer, skin color measurements (melanin index) were taken inner part of arm where the UV rarely hit.  African genetic ancestry was estimated using 33 ancestry informative markers (AIMs).

They found that estimated African ancestry was significantly correlated with melanin index, as expected, but more interestingly melanin index and estimated African ancestry vary greatly.  This means that functional genes that determine the skin color are located somewhere else on the genome and the allele frequencies of these skin pigmentation gene variants differ greatly between ancestral populations (e.g., Africans and Europeans for African Americans).  They explain that because African Americans are recently admixed, we are observing the results of the population structure that existed in their ancestral populations.

Skin color is a very heritable trait.  If skin color is determined largely by genes, one may expect to see small variability of melanin index of African Americans with 100% African ancestry, but that is not the case.  They observed a great variation in melanin index of African Americans with 100% African ancestry.  Because skin color is polygenic traits, there are many different genes that determine the skin color, so natural variation in skin color should exist in Africa.

The research was conducted when only a few candidate genes linked to skin color were found, and they confirmed that two candidate genes for skin pigmentation, TYR and OCA2 are significantly associated with melanin index in African Americans (actually, Shriver and colleagues were working on other projects looking for skin color genes when these articles came
out).

How variable is the skin color and melanin index in Africa?  There are research projects that demonstrated that skin color varies among sub-Saharan African populations, but has anybody systematically investigated how variable the skin color is within an African population?

Genetic evidence of Indian Ocean slave trade from Indian Siddis

Shah, Anish M., R. Tamang, et al. (2011). “Indian Siddis: African Descendants with Indian Admixture.” American Journal of Human Genetics 89(1):154-161.

Compared to Tran-Atlantic slave trade, Indian Ocean Slave trade is less known, maybe less understood, but has longer history.  Indigenous Africans were captured and traded by other Africans, Arabs, and Europeans.  Some of the slaves were sent to Middle East and South Asia.  Sub-Saharan African mtDNA haplogroups have been found among the Middle Eastern populations and the frequencies range from 9 to 34%.  Sub-Saharan African Y chromosome haplogroups are rare, but are also found among the Middle Eastern Arab populations.  Richards et al. (2003) and Quintana-Murci et al. (2004) argue that these sub-Saharan African mtDNA haplogroups were brought to the Middle East and reached South Asian through the Arab slave trade.  African females were incorporated into Islamic societies, but African males did not have much chance of reproduction.

In this article, Shah et al. (2011) demonstrate that Siddis, or Habishis, from India, the descendants of slaves from Africa, have genetic characteristics of sub-Saharan Africans.  They genotyped 850,000 autosomal SNPs, 32 Y chromosome biallelic markers, and 17 Y chromosome STR and sequenced mtDNA hypervariable region I.

Among Siddis, sub-Saharan genetic contribution estimated based on autosomal SNPs is quite large ranging 62.3-74.4% and they are plotted more closely to HapMap Yorubans than Indians, Europeans, or Asians on the PC plot.  Contrary to the previous studies, they found more male sub-Saharan contribution to the Siddis than female contribution.  You could expect this from the Indians marriage rule of endogamy, but gene flow between the Siddis and neighboring ethnic groups or communities was unidirectional.  They found South Asians and Eurasian genetic
contribution to the Siddis from their neighboring communities, but they did not find Sub-Saharan genetic contribution from the Siddis to neighboring ethnic groups.

Genetic studies to understand slave trade are usually conducted using uniparental markers (mtDNA and Y-chromosome).  The molecular genetic and analytical techniques to trace the origin are relatively simple, but the problem is that you are tracing only two lineages (maternal and paternal) out of thousands of possible ancestors for a particular individual.  By analyzing autosomal markers, you are getting genetic information of all the ancestors.  Recent advancement in molecular genetics allows researchers to genotypes many single nucleotide polymorphisms (SNPs) per individual.  Sometime in the future, it will be possible to genotype over 1 million SNPs per individual without huge cost.  Down side of this is that it requires more sophisticated statistical and analytical techniques.

References:

Quintana-Murci L, Chaix R, Wells S, Behar DM, Sayar H, Scozzari R, Rengo C, Al-Zaheri N, Semino O, Santachiara-Benerecetti AS, Coppa A, Ayub Q, Mohyuddin A, Tyler-Smith C, Mehdi SQ, Torroni A, and McElreavey K (2004) Where west meets east: the complex mtDNA landscape of southwest and Central Asian corridor. American Journal of Human Genetics 74:827-845.

Richards M, Rengo C, Cruciani F, Gratrix F, Wilson JF, Scozzari R, Macaulay V, and Torroni A (2003) Extensive female-mediated gene flow from Sub-Saharan Africa into Near Eastern Arab Populaitons. American Journal of Human Genetics 72:1058-1064.

Evolution and human skin color: how do Jablonski and Chaplin explain skin color variation?

Jablonski, N. G. and G. Chaplin (2002). “Skin Deep.” Scientific American October: 74-81.

I have written about Jablonski and her work on evolution of skin color and roles of Vitamin D before (here).  This article published in Scientific America in 2002 is today widely read by undergraduate anthropology students.  In this article, Jablonski and Chaplin reject that skin cancer is the major evolutionary factor for dark-colored skin in Equatorial areas.  They suggest that
Vitamin D and folic acid are two important factors of biological adaptation responding varying level of UV radiation, and cultural adaptation and recent migration were also important factors understanding the observed geographical pattern of skin color.

The people living in equatorial areas, whether they have dark colored or light colored skin, can get enough sun light to synthesize Vitamin D.  However, they have to have dark colored skin to protect them from harmful UV radiation.  Overexposure to the UV radiation can cause skin cancer, and skin cancer is deadly to the individuals, but it does not reduce reproductive success of individuals, because people usually have skin cancer after reproductive age.  Instead, overexposure to UV ration may lead to reduced reproductive success of individuals, because overexposure to UV radiation may reduce the level of folate, an essential Vitamin B, in their blood.  The low level of circulating folate is associated with higher risk of babies with spina bifida and low sperm counts.

For those people living in high latitude areas, where they can get enough sun light to synthesize Vitamin D only in limited time of the year, having light-colored skin is advantageous.  In high latitude areas, people with dark colored skin tend to have low level of circulating Vitamin D, and low level of circulating Vitamin D is associated with problems with bone development and maintenance, and immune system, etc (see here).

Probably, her major contribution is to publicize how evolution can explain skin color variation around the world and to demonstrate that the field of anthropology can help people appreciate the genetic and biological variation that exists in the world.