geographic origins of their ancestors

 

E POLICY FORUM

A t least two dozen companies now market “genetic ancestry tests” to help consumers reconstruct their

family histories and determine the geographic origins of their ancestors. More than 460,000 people have purchased these tests over the past 6 years (1), and public interest is still skyrocketing (1–4). Some scientists support this enterprise because it makes genetics acces- sible and relevant; oth- ers view it with indiffer- ence, seeing the tests as merely “recreational.” However, both scientists and consumers should approach genetic ances- try testing with caution because (i) the tests can have a profound impact on individuals and com- munities, (ii) the assum- ptions and limitations of these tests make them less informative than many realize, and (iii) commercializa- tion has led to misleading practices that rein- force misconceptions.

The Impact of “Recreational Genetics” Although genetic ancestry testing is often described as “recreational genetics,” many consumers do not take these tests lightly. Each test costs $100 to $900, and con- sumers often have deep personal reasons for purchasing these products. Many indi-

viduals hope to identify biological relatives, to vali- date genealogical records, and to f ill in gaps in family histories. Others are searching for a connection to specif ic groups or places in Eurasia and Africa. This search for a “homeland” is particularly poignant for many African- Americans, who hope to recapture a history stolen by slavery. Others seek a more nuanced picture of their genetic back- grounds than the black-and-white dichotomy that dominates U.S. racial thinking.

Genetic ancestry testing also has serious consequences. Test-takers may reshape their personal identities, and they may suffer emo- tional distress if test results are unexpected or undesired (5). Test-takers may also change how they report their race or ethnicity on gov- ernmental forms, college or job applications, and medical questionnaires (6). This could make it more difficult to track the social expe- riences and effects of race and racism (6). Genetic ancestry testing also affects broader communities: Tests have led African-Ameri- cans to visit and financially support specific

African communities. Other Americans have taken the tests in hope of obtaining Native American tribal affiliation (and benefits like financial support, housing, education, health care, and affirmation of identity) or to chal- lenge tribal membership decisions (7).

Limitations It is important to understand what these tests can and cannot determine. Most tests fall into two categories. Mitochondrial DNA (mtDNA)

tests sequence the hypervariable region of the maternally inherited mitochondrial genome. Y-chromosome tests analyze short tandem repeats and/or single nucleo-

tide polymorphisms (SNPs) in the paternally inherited Y chromo- some. In both cases, the test-taker’s haplotype (set of linked alleles) is determined and compared with hap- lotypes from other sampled individu- als. These comparisons can identify related individuals who share a com- mon maternal or paternal ancestor, as well as locations where the test- taker’s haplotype is found today. However, each test examines less

than 1% of the test-taker’s DNA and sheds light on only one ancestor each generation (8). A third type of test (DNAPrint’s Ancestry- ByDNA test) attempts to provide a better measure of overall ancestry by using 175 autosomal markers (inherited from both parents) to estimate an individual’s “bio- geographical ancestry.”

Although companies acknowledge that mtDNA and Y-chromosome tests provide no information about most of a test-taker’s ances- tors, more important limitations to all three types of genetic ancestry tests are often less obvious. For example, genetic ancestry testing can identify some of the groups and locations around the world where a test-taker’s haplo- type or autosomal markers are found, but it is unlikely to identify all of them. Such infer- ences depend on the samples in a company’s database, and even databases with 10,000 to 20,000 samples may fail to capture the full array of human genetic diversity in a particu- lar population or region.

Commercially available tests of genetic

ancestry have significant scientific limitations,

but are serious matters for many test-takers.

The Science and Business of Genetic Ancestry Testing Deborah A. Bolnick,1* Duana Fullwiley,2 Troy Duster,3,4 Richard S. Cooper,5 Joan H. Fujimura,6

Jonathan Kahn,7 Jay S. Kaufman,8 Jonathan Marks,9 Ann Morning,3 Alondra Nelson,10 Pilar

Ossorio,11 Jenny Reardon,12 Susan M. Reverby,13 Kimberly TallBear14,15

G E N E T I C S

1Department of Anthropology, University of Texas, Austin, TX 78712, USA. 2Departments of Anthropology and African and African-American Studies, Harvard University, Cambridge, MA; 3Department of Sociology, New York University, New York, NY; 4Department of Sociology, University of California, Berkeley, CA; 5Department of Preventive Medicine and Epidemiology, Loyola University Chicago Stritch School of Medicine, Maywood, IL; 6Department of Sociology, University of Wisconsin, Madison, WI; 7Hamline University School of Law, St. Paul, MN; 8Department of Epidemiology, University of North Carolina School of Public Health, Chapel Hill, NC; 9Department of Anthropology, University of North Carolina, Charlotte, NC; 10Departments of Sociology and African American Studies, Yale University, New Haven, CT; 11University of Wisconsin Law School, Madison, WI; 12Department of Sociology, University of California, Santa Cruz, CA; 13Department of Women’s Studies, Wellesley College, Wellesley, MA; 14Department of American Indian Studies, Arizona State University, Tempe, AZ; 15Department of Environmental Science, Policy and Management, and Rhetoric, University of California, Berkeley, CA; USA.

*Author for correspondence. E-mail: deborah.bolnick@ mail.utexas.edu

Published by AAAS

 

 

19 OCTOBER 2007 VOL 318 SCIENCE www.sciencemag.org400

POLICYFORUM

Another problem is that questionable sci-

entific assumptions are sometimes made

when companies report results of a genetic

ancestry test. For instance, when an allele or

haplotype is most common in one popula-

tion, companies often assume it to be diag-

nostic of that population. This can be prob-

lematic because high genetic diversity exists

within populations and gene flow occurs

between populations. Very few alleles are

therefore diagnostic of membership in a spe-

cific population (9), but companies some-

times fail to mention that an allele could have

been inherited from a population in which it

is less common. Consequently, many con-

sumers do not realize that the tests are proba-

bilistic and can reach incorrect conclusions.

Consumers often purchase these tests to

learn about their race or ethnicity, but there is

no clear-cut connection between an individ-

ual’s DNA and his or her racial or ethnic affil-

iation. Worldwide patterns of human genetic

diversity are weakly correlated with racial and

ethnic categories because both are partially

correlated with geography (9). Current under-

standings of race and ethnicity reflect more

than genetic relatedness, though, having been

defined in particular sociohistorical contexts

(i.e., European and American colonialism). In

addition, social relationships and life experi-

ences have been as important as biological

ancestry in shaping individual identity and

group membership.

Many genetic ancestry tests also claim to

tell consumers where their ancestral lineage

originated and the social group to which their

ancestors belonged. However, present-day

patterns of residence are rarely identical to

what existed in the past, and social groups

have changed over time, in name and compo-

sition (10). Databases of present-day samples

may therefore provide false leads.

Finally, even though there is little evidence

that four biologically discrete groups of

humans ever existed (9), the AncestryByDNA

test creates the appearance of genetically dis-

tinct populations by relying on “ancestry

informative markers” (AIMs). AIMs are SNPs

or other markers that show relatively large (30

to 50%) frequency differences between popula-

tion samples. The AncestryByDNA test exam-

ines AIMs selected to differentiate between

four “parental” populations (Africans,

Europeans, East Asians, and Native Ameri-

cans). However, these AIMs are not found in all

peoples who would be classed together as a

given “parental” population. The AIMs that

characterize “Africans,” for example, were cho-

sen on the basis of a sample of West Africans.

Dark-skinned East Africans might be omitted