“There is so much diversity in Africans that there is no such thing as an African race.”

Posted in Excerpts/Quotes on 2018-02-20 00:57Z by Steven

The study adds to established research undercutting old notions of race. You can’t use skin color to classify humans, any more than you can use other complex traits like height, [Sarah] Tishkoff says. “There is so much diversity in Africans that there is no such thing as an African race.”

Ann Gibbons, “New gene variants reveal the evolution of human skin color,” Science, October 12, 2017. http://www.sciencemag.org/news/2017/10/new-gene-variants-reveal-evolution-human-skin-color.

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New gene variants reveal the evolution of human skin color

Posted in Africa, Articles, Health/Medicine/Genetics, Media Archive on 2018-02-20 00:53Z by Steven

New gene variants reveal the evolution of human skin color

Science
2017-11-12

Ann Gibbons, Contributing Correspondent


Researchers have identified genes that help create diverse skin tones, such as those seen in the Agaw (left) and Surma (right) peoples of Africa.
ALESSIA RANCIARO & DR. SIMON R. THOMPSON

Most people associate Africans with dark skin. But different groups of people in Africa have almost every skin color on the planet, from deepest black in the Dinka of South Sudan to beige in the San of South Africa. Now, researchers have discovered a handful of new gene variants responsible for this palette of tones.

The study, published online this week in Science, traces the evolution of these genes and how they traveled around the world. While the dark skin of some Pacific Islanders can be traced to Africa, gene variants from Eurasia also seem to have made their way back to Africa. And surprisingly, some of the mutations responsible for lighter skin in Europeans turn out to have an ancient African origin.

“This is really a landmark study of skin color diversity,” says geneticist Greg Barsh of the HudsonAlpha Institute for Biotechnology in Huntsville, Alabama.

Researchers agree that our early australopithecine ancestors in Africa probably had light skin beneath hairy pelts. “If you shave a chimpanzee, its skin is light,” says evolutionary geneticist Sarah Tishkoff of the University of Pennsylvania, the lead author of the new study. “If you have body hair, you don’t need dark skin to protect you from ultraviolet [UV] radiation.”

Until recently, researchers assumed that after human ancestors shed most body hair, sometime before 2 million years ago, they quickly evolved dark skin for protection from skin cancer and other harmful effects of UV radiation. Then, when humans migrated out of Africa and headed to the far north, they evolved lighter skin as an adaptation to limited sunlight. (Pale skin synthesizes more vitamin D when light is scarce.)…

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Loci associated with skin pigmentation identified in African populations

Posted in Africa, Articles, Health/Medicine/Genetics, Media Archive on 2017-12-04 01:50Z by Steven

Loci associated with skin pigmentation identified in African populations

Science
2017-10-12
eaan8433
DOI: 10.1126/science.aan8433

Nicholas G. Crawford, Derek E. Kelly, Matthew E. B. Hansen, Marcia H. Beltrame, Shaohua Fan, Shanna L. Bowman, Ethan Jewett, Alessia Ranciaro, Simon Thompson, Yancy Lo, Susanne P. Pfeifer, Jeffrey D. Jensen, Michael C. Campbell, William Beggs, Farhad Hormozdiari, Sununguko Wata Mpoloka, Gaonyadiwe George Mokone, Thomas Nyambo, Dawit Wolde Meskel, Gurja Belay, Jake Haut, NISC Comparative Sequencing Program, Harriet Rothschild, Leonard Zon, Yi Zhou, Michael A. Kovacs, Mai Xu, Tongwu Zhang, Kevin Bishop, Jason Sinclair, Cecilia Rivas, Eugene Elliot, Jiyeon Choi, Shengchao A. Li, Belynda Hicks, Shawn Burgess, Christian Abnet, Dawn E. Watkins-Chow, Elena Oceana, Yun S. Song, Eleazar Eskin, Kevin M. Brown, Michael S. Marks, Stacie K. Loftus, William J. Pavan, Meredith Yeager, Stephen Chanock, Sarah Tishkoff

Despite the wide range of skin pigmentation in humans, little is known about its genetic basis in global populations. Examining ethnically diverse African genomes, we identify variants in or near SLC24A5, MFSD12, DDB1, TMEM138, OCA2 and HERC2 that are significantly associated with skin pigmentation. Genetic evidence indicates that the light pigmentation variant at SLC24A5 was introduced into East Africa by gene flow from non-Africans. At all other loci, variants associated with dark pigmentation in Africans are identical by descent in southern Asian and Australo-Melanesian populations. Functional analyses indicate that MFSD12 encodes a lysosomal protein that affects melanogenesis in zebrafish and mice, and that mutations in melanocyte-specific regulatory regions near DDB1/TMEM138 correlate with expression of UV response genes under selection in Eurasians.

Variation in epidermal pigmentation is a striking feature of modern humans. Human pigmentation is correlated with geographic and environmental variation (Fig. 1). Populations at lower latitudes have darker pigmentation than populations at higher latitudes, suggesting that skin pigmentation is an adaptation to differing levels of ultraviolet radiation (UVR) (1). Because equatorial regions receive more UVR than temperate regions, populations from these regions (including sub-Saharan Africans, South Asians, and Australo-Melanesians) have darker pigmentation (Fig. 1), which likely mitigates the negative impact of high UVR exposure such as skin cancer and folate degradation (1). In contrast, the synthesis of vitamin D3 in response to UVR, needed to prevent rickets, may drive selection for light pigmentation at high latitudes (1).

The basal layer of human skin contains melanocytes, specialized pigment cells that harbor subcellular organelles called melanosomes in which melanin pigments are synthesized and stored and then transferred to keratinocytes (2). Melanosome morphology and content differs between melanocytes that synthesize mainly eumelanins (black-brown pigments) or pheomelanins (pigments which range from yellow to reddish-brown) (3). Variation in skin pigmentation is due to the type and quantity of melanins generated, melanosome size, and the manner in which keratinocytes sequester and degrade melanins (4).

While over 350 pigmentation genes have been identified in animal models, only a subset of these genes have been linked to normal variation in humans (5). Of these, there is limited knowledge about loci that affect pigmentation in populations with African ancestry (6, 7).

Skin pigmentation is highly variable within Africa

To identify genes affecting skin pigmentation in Africa, we used a DSM II ColorMeter to quantify light reflectance from the inner arm as a proxy for melanin levels in 2,092 ethnically and genetically diverse Africans living in Ethiopia, Tanzania, and Botswana (table S1 and figs. S1 and S2) (8). Skin pigmentation levels vary extensively among Africans, with darkest pigmentation observed in Nilo-Saharan speaking pastoralist populations in Eastern Africa and lightest pigmentation observed in San hunter-gatherer populations from southern Africa (Fig. 2 and table S1)…

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Departure of U.S. Census director threatens 2020 count

Posted in Articles, Census/Demographics, Media Archive, Politics/Public Policy, United States on 2017-05-11 02:01Z by Steven

Departure of U.S. Census director threatens 2020 count

Science
2017-05-09

Jeffrey Mervis


John Thompson will leave the Census Bureau on 30 June. U.S. Census Bureau

John Thompson is stepping down next month as director of the U.S. Census Bureau. His announcement today comes less than 1 week after a congressional spending panel grilled him about mounting problems facing the agency in preparing for the 2020 decennial census. And Thompson’s pending retirement is weighing heavily on the U.S. statistical community.

Thompson is leaving halfway through a 1-year extension of a term that expired last December. His departure will create what a 2011 law was expressly designed to avoid—a leadership vacuum during a crucial time in the 10-year life cycle of the census, the nation’s largest civilian undertaking. The immediate concern is who the Trump administration will appoint, and how soon it will act…

Ken Prewitt, who led the agency from 1998 to 2001, worries that a long delay in naming a well-qualified replacement for Thompson could be the first step of a long, steep decline in the quality of the federal statistic system, which spans 13 agencies. “That system is fragile, and it wouldn’t take much to damage it severely,” says Prewitt, a professor of social affairs at Columbia University. “My real fear is that they don’t care enough to do a good job with the 2020 census. And then after doing a bad job, they decide to let the private sector take over.”…

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Taking race out of human genetics

Posted in Articles, Health/Medicine/Genetics, Media Archive, Politics/Public Policy, Social Science on 2016-02-06 17:35Z by Steven

Taking race out of human genetics

Science
Volume 351, Issue 6273 (2016-02-05)
pages 564-565
DOI: 10.1126/science.aac4951

Michael Yudell, Associate Professor
Dornsife School of Public Health Department of Community Health and Prevention
Drexel University, Philadelphia, Pennsylvania

Dorothy Roberts, George A. Weiss University Professor of Law and Sociology and the Raymond Pace and Sadie Tanner Mossell Alexander Professor of Civil Rights
University of Pennsylvania

Rob DeSalle, Curator, Molecular Systematics; Principal Investigator, SICG Genomics Lab; Professor, Richard Gilder Graduate School
American Museum of Natural History, New York, New York

Sarah Tishkoff, David and Lyn Silfen University Professor in Genetics and Biology
University of Pennsylvania

In the wake of the sequencing of the human genome in the early 2000s, genome pioneers and social scientists alike called for an end to the use of race as a variable in genetic research (1, 2). Unfortunately, by some measures, the use of race as a biological category has increased in the postgenomic age (3). Although inconsistent definition and use has been a chief problem with the race concept, it has historically been used as a taxonomic categorization based on common hereditary traits (such as skin color) to elucidate the relationship between our ancestry and our genes. We believe the use of biological concepts of race in human genetic research—so disputed and so mired in confusion—is problematic at best and harmful at worst. It is time for biologists to find a better way.

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How Europeans evolved white skin

Posted in Articles, Europe, Health/Medicine/Genetics, Media Archive on 2015-04-06 01:26Z by Steven

How Europeans evolved white skin

Science
2015-04-02
DOI: 10.1126/science.aab2435

Ann Gibbons, Contributing Correspondent

ST. LOUIS, MISSOURI—Most of us think of Europe as the ancestral home of white people. But a new study shows that pale skin, as well as other traits such as tallness and the ability to digest milk as adults, arrived in most of the continent relatively recently. The work, presented here last week at the 84th annual meeting of the American Association of Physical Anthropologists, offers dramatic evidence of recent evolution in Europe and shows that most modern Europeans don’t look much like those of 8000 years ago.

The origins of Europeans have come into sharp focus in the past year as researchers have sequenced the genomes of ancient populations, rather than only a few individuals. By comparing key parts of the DNA across the genomes of 83 ancient individuals from archaeological sites throughout Europe, the international team of researchers reported earlier this year that Europeans today are a mix of the blending of at least three ancient populations of hunter-gatherers and farmers who moved into Europe in separate migrations over the past 8000 years. The study revealed that a massive migration of Yamnaya herders from the steppes north of the Black Sea may have brought Indo-European languages to Europe about 4500 years ago.

Now, a new study from the same team drills down further into that remarkable data to search for genes that were under strong natural selection—including traits so favorable that they spread rapidly throughout Europe in the past 8000 years. By comparing the ancient European genomes with those of recent ones from the 1000 Genomes Project, population geneticist Iain Mathieson, a postdoc in the Harvard University lab of population geneticist David Reich, found five genes associated with changes in diet and skin pigmentation that underwent strong natural selection…

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Mexico boasts a staggering genetic diversity, study shows

Posted in Caribbean/Latin America, Health/Medicine/Genetics, Media Archive, Mexico on 2014-07-02 01:45Z by Steven

Mexico boasts a staggering genetic diversity, study shows

Los Angeles Times
2014-06-12

Geoffrey Mohan

SHARELINES

▼ DNA offers a nuanced answer to what it means to be Mexican
▼ Ancient genetic signal survived conquest in Mexico
▼ Latino and Hispanic labels don’t do justice to Mexico’s genome

Writers, artists and historians have long pondered what it means to be Mexican. Now science has offered its answer, and it could change how medicine uses racial and ethnic categories to assess disease risk, testing and treatment..

The broadest analysis of the Mexican genome ever undertaken reveals a nation of staggering genetic diversity, where European conquest only thinly masks the ancestral DNA of Native Americans, and where some populations remain as distinct from one another as Europeans are from Chinese, according to findings published Thursday in the journal Science.

Forty researchers, who share Latino heritage as well as professional qualms over the significance of ethnic and racial categories, teamed up across borders to analyze more than 1 million variations in the building blocks of DNA. They examined more than 500 samples collected in Mexico’s remote Indian villages and polyglot cities, and from Mexican Americans in California.

“Because these populations are so rich, so genetically differentiated, you can’t just lump them all in,” said lead investigator Carlos Bustamante, a population geneticist and co-director of Stanford University’s Center for Computational, Evolutionary and Human Genomics. “You really have to embrace that diversity and think about doing medical genetic studies on a very large scale.”

To illustrate their point, the researchers compared their new genetic data with the results of lung function tests for children in Mexico City and Latinos in the San Francisco Bay Area. They discovered that pulmonary function varied in ways that were mirrored in DNA. It was as if someone with a fraction of Maya ancestry had lungs that were 10 years older than someone with a bit of northern indigenous heritage…

…Researchers not involved in the study, however, caution that correlations between disease risk and ancestry may not have much of a genetic basis at all. In many cases, they might mask socioeconomic or environmental factors — where and how you live.

The suggestion that differences in DNA are responsible for observed differences in lung capacity “is an enormous leap,” said UC Berkeley sociologist Troy Duster, who has written extensively on the intersection of race, biology and public policy.

Lundy Braun, an Africana studies professor at Brown University who studies the intersection of race and medicine, said medicine’s focus on genetics may be overshadowing other avenues of research.

“The effects of social class on lung function have been largely ignored in favor of the focus on race and ethnic difference,” she said.

Braun and Duster worry that such genomic studies may unwittingly lend legitimacy to widely discredited ideas about racial disparities.

“There is always lurking danger that this kind of research, which emphasizes the genetic structure of ethnic and racial groups, fuels the notion that the biology or genetics of those groups explains their condition,” Duster said…

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