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FW: [ANTHRO-L] Scientific American: Does Race Exist?

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  • Popplestone, Ann
    ... From: Anthro-L [mailto:Anthro-l@listserv.buffalo.edu] On Behalf Of Scupin, Ray Sent: Friday, November 14, 2003 12:25 PM To: ANTHRO-L@LISTSERV.BUFFALO.EDU
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      -----Original Message-----
      From: Anthro-L [mailto:Anthro-l@...] On Behalf Of Scupin, Ray
      Sent: Friday, November 14, 2003 12:25 PM
      To: ANTHRO-L@...
      Subject: [ANTHRO-L] Scientific American: Does Race Exist?

      Scientific American: Does Race Exist?
      November 10, 2003

         If races are defined as genetically discrete groups, no. But
         researchers can use some genetic information to group individuals into
         clusters with medical relevance
         By Michael J. Bamshad and Steve E. Olson

         Look around on the streets of any major city, and you will see a
         sampling of the outward variety of humanity: skin tones ranging from
         milk-white to dark brown; hair textures running the gamut from fine
         and stick-straight to thick and wiry. People often use physical
         characteristics such as these--along with area of geographic origin
         and shared culture--to group themselves and others into "races." But
         how valid is the concept of race from a biological standpoint? Do
         physical features reliably say anything informative about a person's
         genetic makeup beyond indicating that the individual has genes for
         blue eyes or curly hair?

         The problem is hard in part because the implicit definition of what
         makes a person a member of a particular race differs from region to
         region across the globe. Someone classified as "black" in the U.S.,
         for instance, might be considered "white" in Brazil and "colored" (a
         category distinguished from both "black" and "white") in South Africa.

         Yet common definitions of race do sometimes work well to divide groups
         according to genetically determined propensities for certain diseases.
         Sickle cell disease is usually found among people of largely African
         or Mediterranean descent, for instance, whereas cystic fibrosis is far
         more common among those of European ancestry. In addition, although
         the results have been controversial, a handful of studies have
         suggested that African-Americans are more likely to respond poorly to
         some drugs for cardiac disease than are members of other groups.

         Over the past few years, scientists have collected data about the
         genetic constitution of populations around the world in an effort to
         probe the link between ancestry and patterns of disease. These data
         are now providing answers to several highly emotional and contentious
         questions: Can genetic information be used to distinguish human groups
         having a common heritage and to assign individuals to particular ones?
         Do such groups correspond well to predefined descriptions now widely
         used to specify race? And, more practically, does dividing people by
         familiar racial definitions or by genetic similarities say anything
         useful about how members of those groups experience disease or respond
         to drug treatment?

         In general, we would answer the first question yes, the second no, and
         offer a qualified yes to the third. Our answers rest on several
         generalizations about race and genetics. Some groups do differ
         genetically from others, but how groups are divided depends on which
         genes are examined; simplistically put, you might fit into one group
         based on your skin-color genes but another based on a different
         characteristic. Many studies have demonstrated that roughly 90 percent
         of human genetic variation occurs within a population living on a
         given continent, whereas about 10 percent of the variation
         distinguishes continental populations. In other words, individuals
         from different populations are, on average, just slightly more
         different from one another than are individuals from the same
         population. Human populations are very similar, but they often can be

         Classifying Humans
         As a first step to identifying links between social definitions of
         race and genetic heritage, scientists need a way to divide groups
         reliably according to their ancestry. Over the past 100,000 years or
         so, anatomically modern humans have migrated from Africa to other
         parts of the world, and members of our species have increased
         dramatically in number. This spread has left a distinct signature in
         our DNA.

         To determine the degree of relatedness among groups, geneticists rely
         on tiny variations, or polymorphisms, in the DNA--specifically in the
         sequence of base pairs, the building blocks of DNA. Most of these
         polymorphisms do not occur within genes, the stretches of DNA that
         encode the information for making proteins (the molecules that
         constitute much of our bodies and carry out the chemical reactions of
         life). Accordingly, these common variations are neutral, in that they
         do not directly affect a particular trait. Some polymorphisms do occur
         in genes, however; these can contribute to individual variation in
         traits and to genetic diseases.

         As scientists have sequenced the human genome (the full set of nuclear
         DNA), they have also identified millions of polymorphisms. The
         distribution of these polymorphisms across populations reflects the
         history of those populations and the effects of natural selection. To
         distinguish among groups, the ideal genetic polymorphism would be one
         that is present in all the members of one group and absent in the
         members of all other groups. But the major human groups have separated
         from one another too recently and have mixed too much for such
         differences to exist.

         Polymorphisms that occur at different frequencies around the world
         can, however, be used to sort people roughly into groups. One useful
         class of polymorphisms consists of the Alus, short pieces of DNA that
         are similar in sequence to one another. Alus replicate occasionally,
         and the resulting copy splices itself at random into a new position on
         the original chromosome or on another chromosome, usually in a
         location that has no effect on the functioning of nearby genes. Each
         insertion is a unique event. Once an Alu sequence inserts itself, it
         can remain in place for eons, getting passed from one person to his or
         her descendants. Therefore, if two people have the same Alu sequence
         at the same spot in their genome, they must be descended from a common
         ancestor who gave them that specific segment of DNA.

         One of us (Bamshad), working with University of Utah scientists Lynn
         B. Jorde, Stephen Wooding and W. Scott Watkins and with Mark A. Batzer
         of Louisiana State University, examined 100 different Alu
         polymorphisms in 565 people born in sub-Saharan Africa, Asia and
         Europe. First we determined the presence or absence of the 100 Alus in
         each of the 565 people. Next we removed all the identifying labels
         (such as place of origin and ethnic group) from the data and sorted
         the people into groups using only their genetic information.

         Our analysis yielded four different groups. When we added the labels
         back to see whether each individual's group assignment correlated to
         common, predefined labels for race or ethnicity, we saw that two of
         the groups consisted only of individuals from sub-Saharan Africa, with
         one of those two made up almost entirely of Mbuti Pygmies. The other
         two groups consisted only of individuals from Europe and East Asia,
         respectively. We found that we needed 60 Alu polymorphisms to assign
         individuals to their continent of origin with 90 percent accuracy. To
         achieve nearly 100 percent accuracy, however, we needed to use about
         100 Alus.

         Other studies have produced comparable results. Noah A. Rosenberg and
         Jonathan K. Pritchard, geneticists formerly in the laboratory of
         Marcus W. Feldman of Stanford University, assayed approximately 375
         polymorphisms called short tandem repeats in more than 1,000 people
         from 52 ethnic groups in Africa, Asia, Europe and the Americas. By
         looking at the varying frequencies of these polymorphisms, they were
         able to distinguish five different groups of people whose ancestors
         were typically isolated by oceans, deserts or mountains: sub-Saharan
         Africans; Europeans and Asians west of the Himalayas; East Asians;
         inhabitants of New Guinea and Melanesia; and Native Americans. They
         were also able to identify subgroups within each region that usually
         corresponded with each member's self-reported ethnicity.

         The results of these studies indicate that genetic analyses can
         distinguish groups of people according to their geographic origin. But
         caution is warranted. The groups easiest to resolve were those that
         were widely separated from one another geographically. Such samples
         maximize the genetic variation among groups. When Bamshad and his
         co-workers used their 100 Alu polymorphisms to try to classify a
         sample of individuals from southern India into a separate group, the
         Indians instead had more in common with either Europeans or Asians. In
         other words, because India has been subject to many genetic influences
         from Europe and Asia, people on the subcontinent did not group into a
         unique cluster. We concluded that many hundreds--or perhaps
         thousands--of polymorphisms might have to be examined to distinguish
         between groups whose ancestors have historically interbred with
         multiple populations.

         The Human Race
         Given that people can be sorted broadly into groups using genetic
         data, do common notions of race correspond to underlying genetic
         differences among populations? In some cases they do, but often they
         do not. For instance, skin color or facial features--traits influenced
         by natural selection--are routinely used to divide people into races.
         But groups with similar physical characteristics as a result of
         selection can be quite different genetically. Individuals from
         sub-Saharan Africa and Australian Aborigines might have similar skin
         pigmentation (because of adapting to strong sun), but genetically they
         are quite dissimilar.

         In contrast, two groups that are genetically similar to each other
         might be exposed to different selective forces. In this case, natural
         selection can exaggerate some of the differences between groups,
         making them appear more dissimilar on the surface than they are
         underneath. Because traits such as skin color have been strongly
         affected by natural selection, they do not necessarily reflect the
         population processes that have shaped the distribution of neutral
         polymorphisms such as Alus or short tandem repeats. Therefore, traits
         or polymorphisms affected by natural selection may be poor predictors
         of group membership and may imply genetic relatedness where, in fact,
         little exists.

         Another example of how difficult it is to categorize people involves
         populations in the U.S. Most people who describe themselves as
         African-American have relatively recent ancestors from West Africa,
         and West Africans generally have polymorphism frequencies that can be
         distinguished from those of Europeans, Asians and Native Americans.
         The fraction of gene variations that African-Americans share with West
         Africans, however, is far from uniform, because over the centuries
         African-Americans have mixed extensively with groups originating from
         elsewhere in Africa and beyond.

         Over the past several years, Mark D. Shriver of Pennsylvania State
         University and Rick A. Kittles of Howard University have defined a set
         of polymorphisms that they have used to estimate the fraction of a
         person's genes originating from each continental region. They found
         that the West African contribution to the genes of individual
         African-Americans averages about 80 percent, although it ranges from
         20 to 100 percent. Mixing of groups is also apparent in many
         individuals who believe they have only European ancestors. According
         to Shriver's analyses, approximately 30 percent of Americans who
         consider themselves "white" have less than 90 percent European
         ancestry. Thus, self-reported ancestry is not necessarily a good
         predictor of the genetic composition of a large number of Americans.
         Accordingly, common notions of race do not always reflect a person's
         genetic background.

         Membership Has Its Privileges
         Understanding the relation between race and genetic variation has
         important practical implications. Several of the polymorphisms that
         differ in frequency from group to group have specific effects on
         health. The mutations responsible for sickle cell disease and some
         cases of cystic fibrosis, for instance, result from genetic changes
         that appear to have risen in frequency because they were protective
         against diseases prevalent in Africa and Europe, respectively. People
         who inherit one copy of the sickle cell polymorphism show some
         resistance to malaria; those with one copy of the cystic fibrosis
         trait may be less prone to the dehydration resulting from cholera. The
         symptoms of these diseases arise only in the unfortunate individuals
         who inherit two copies of the mutations.

         Genetic variation also plays a role in individual susceptibility to
         one of the worst scourges of our age: AIDS. Some people have a small
         deletion in both their copies of a gene that encodes a particular
         cell-surface receptor called chemokine receptor 5 (CCR5). As a result,
         these individuals fail to produce CCR5 receptors on the surface of
         their cells. Most strains of HIV-1, the virus that causes AIDS, bind
         to the CCR5 receptor to gain entry to cells, so people who lack CCR5
         receptors are resistant to HIV-1 infection. This polymorphism in the
         CCR5 receptor gene is found almost exclusively in groups from
         northeastern Europe.

         Several polymorphisms in CCR5 do not prevent infection but instead
         influence the rate at which HIV-1 infection leads to AIDS and death.
         Some of these polymorphisms have similar effects in different
         populations; others only alter the speed of disease progression in
         selected groups. One polymorphism, for example, is associated with
         delayed disease progression in European-Americans but accelerated
         disease in African-Americans. Researchers can only study such
         population-specific effects--and use that knowledge to direct
         therapy--if they can sort people into groups.

         In these examples--and others like them--a polymorphism has a
         relatively large effect in a given disease. If genetic screening were
         inexpensive and efficient, all individuals could be screened for all
         such disease-related gene variants. But genetic testing remains
         costly. Perhaps more significantly, genetic screening raises concerns
         about privacy and consent: some people might not want to know about
         genetic factors that could increase their risk of developing a
         particular disease. Until these issues are resolved further,
         self-reported ancestry will continue to be a potentially useful
         diagnostic tool for physicians.

         Ancestry may also be relevant for some diseases that are widespread in
         particular populations. Most common diseases, such as hypertension and
         diabetes, are the cumulative results of polymorphisms in several
         genes, each of which has a small influence on its own. Recent research
         suggests that polymorphisms that have a particular effect in one group
         may have a different effect in another group. This kind of complexity
         would make it much more difficult to use detected polymorphisms as a
         guide to therapy. Until further studies are done on the genetic and
         environmental contributions to complex diseases, physicians may have
         to rely on information about an individual's ancestry to know how best
         to treat some diseases.

         Race and Medicine
         But the importance of group membership as it relates to health care
         has been especially controversial in recent years. Last January the
         U.S. Food and Drug Administration issued guidelines advocating the
         collection of race and ethnicity data in all clinical trials. Some
         investigators contend that the differences between groups are so small
         and the historical abuses associated with categorizing people by race
         so extreme that group membership should play little if any role in
         genetic and medical studies. They assert that the FDA should abandon
         its recommendation and instead ask researchers conducting clinical
         trials to collect genomic data on each individual. Others suggest that
         only by using group membership, including common definitions of race
         based on skin color, can we understand how genetic and environmental
         differences among groups contribute to disease. This debate will be
         settled only by further research on the validity of race as a
         scientific variable.

         A set of articles in the March 20 issue of the New England Journal of
         Medicine debated both sides of the medical implications of race. The
         authors of one article--Richard S. Cooper of the Loyola Stritch School
         of Medicine, Jay S. Kaufman of the University of North Carolina at
         Chapel Hill and Ryk Ward of the University of Oxford--argued that race
         is not an adequate criterion for physicians to use in choosing a
         particular drug for a given patient. They pointed out two findings of
         racial differences that are both now considered questionable: that a
         combination of certain blood vesseldilating drugs was more effective
         in treating heart failure in people of African ancestry and that
         specific enzyme inhibitors (angiotensin converting enzyme, or ACE,
         inhibitors) have little efficacy in such individuals. In the second
         article, a group led by Neil Risch of Stanford University countered
         that racial or ethnic groups can differ from one another genetically
         and that the differences can have medical importance. They cited a
         study showing that the rate of complications from type 2 diabetes
         varies according to race, even after adjusting for such factors as
         disparities in education and income.

         The intensity of these arguments reflects both scientific and social
         factors. Many biomedical studies have not rigorously defined group
         membership, relying instead on inferred relationships based on racial
         categories. The dispute over the importance of group membership also
         illustrates how strongly the perception of race is shaped by different
         social and political perspectives.

         In cases where membership in a geographically or culturally defined
         group has been correlated with health-related genetic traits, knowing
         something about an individual's group membership could be important
         for a physician. And to the extent that human groups live in different
         environments or have different experiences that affect health, group
         membership could also reflect nongenetic factors that are medically

         Regardless of the medical implications of the genetics of race, the
         research findings are inherently exciting. For hundreds of years,
         people have wondered where various human groups came from and how
         those groups are related to one another. They have speculated about
         why human populations have different physical appearances and about
         whether the biological differences between groups are more than skin
         deep. New genetic data and new methods of analysis are finally
         allowing us to approach these questions. The result will be a much
         deeper understanding of both our biological nature and our human

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