race genetic world

8/13/2019 Race Genetic World

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H arva rd M ag az in e 63

But now, says Fullwiley, assistant profes-sor of anthropology and of African andAfrican American studies, genetic meth-ods, with their precision and implied accu-racy, are being used in the same way that

physical appearance has historically beenused: to buildto literally constructcer-tain ideas about why race matters.

Genetic science has revolutionized biol-ogy and medicine, and even rewritten ourunderstanding of human history. But thefact that human beings are 99.9 percentidentical genetically, as Francis Collins andCraig Venter jointly announced at theWhite House on June 26, 2000, when therough draft of the human genome was re-leased, risks being lost, some scholars fear,in an emphasis on human genetic dier-

ence. Both in federally funded scientific re-search and in increasingly popular prac-ticesuch as ancestry testing, which oftenpurports to prove or disprove membershipin a particular race, group, or tribege-netic testing has appeared to lend scientificcredence to the idea that there is a biologi-cal basis for racial categories.

In fact, There is no genetic basis forrace, says Fullwiley, who has studied theethical, legal, and social implications ofthe human genome project with sociolo-gist Troy Duster at UC, Berkeley. She

sometimes quotes Richard Lewontin, nowprofessor of biology and Agassiz professorof zoology emeritus, who said much thesame thing in 1972, when he discoveredthat of all human genetic variation (whichwe now know to be just 0.1 percent of allgenetic material), 85 percent occurs withingeographically distinct groups, while 15percent or less occurs between them. Theissue today, Fullwiley says, is that manyscientists are mining that 15 percent insearch of human dierences by continent.

Last October, Fullwiley and colleaguesfrom 14 academic institutions around thecountry articulated some of their con-cerns about ancestry testing in Sciencemagazine. More than half a million peoplehave paid between $100 and $900 for suchtests, and for somethose seeking to es-tablish membership in a Native Americantribe poised to open a lucrative casino, forexamplethe stakes can be high. Unfor-tunately, the Science authors noted, thetests have serious limitations.

Most tests focus on just two types of

DNA: the paternally inherited Y sex chro-mosome that only men carry, and mito-chondrial DNA, which is passed exclu-sively from mothers to their children.Scientists favor these markers with good

reason: because only one parent can passthem to ospring, they are not subject torecombination, the reshuing of geneticdata that normally occurs in each genera-tion. But they represent less than 1 percentof a subjects DNA, and each tells aboutonly one ancestor per generation. Twogenerations back, a customer might learnabout one of four grandparents; three gen-erations back, about one of eight great-grandparents; and by 10 generations back(roughly 250 years ago), such genetic testsreference just one of the 1,024 ancestors in

that generation. It doesnt take long toreach the point when, mathematically, apersons ancestors start to outnumber thesum total of all people who have ever lived.

Nor can genetic tests verify a personsrace or ethnicity. Genes that aect skinpigmentation or blood proteins involved inmalarial resistance, the authors note, maynot measure direct and unique ancestry(for example, a founder eect), but reflectinstead an evolutionary response toshared environmental exposures. Fur-thermore, the tests are based on compar-

isons to databases of DNA from living pop-ulations, and are therefore vulnerable tosystematic bias because of incompletegeographic sampling or the fact that pre-sent-day patterns of residence are rarelyidentical to what existed in the past. Onetesting company even uses an underlyingmodel that reinforces the archaic racialview that four discrete parental popula-tions (Africans, Europeans, East Asians,and Native Americans) existed in the pasteven though there is little evidence thatfour biologically discrete groups of hu-mans ever existed.

Recently, Fullwileys concerns havecentered on a new kind of genetic testing.For a substantial fee, companies such as23andMe will tell you what your pro-pensity is for hypertension, schizophre-nia, breast cancer, lactose intolerance, andhigh or low IQ, she says. But the studiesthat have established links between genesand these outcomes are probabilistic, shesays, and convey, like ancestry tests, whatmight be called a false precision. Except

for known Mendelian traits or conditions(such as Huntingtons disease) only afraction of people with a gene variantlinked to a disease actually become ill.

Lost in the discussion about genes, she

fears, are epigenetic influences: factorsthat aect gene expression but are not partof ones genetic code, such as prenatal nu-trition (which may influence rates of heartdisease late in life). Such biosocial fac-torsenvironmental, cultural, and eco-nomiccan sometimes be more influentialthan genes. Fullwiley questions, for exam-

ple, if the prevalence of diabetes among Na-tive Americans on reservations, or ofasthma among U.S. Latinos, is only genetic.Her research in Senegal has reinforced thatdoubt. Scientists have long searched for agenetic dierence that would explain whymany Senegalese experience a relativelymild form of sickle cell disease. Fullwileyswork suggests that many of them may in-stead be mitigating their symptoms with awidespread cultural practice: phyto-therapythe ingestion of roots from aplant that, preliminary studies suggest,triggers production of fetal hemoglobin,a blood-cell ty pe that doesnt sickle.When environmental history, or evolu-

Ph o t o g ra p h b y S t u R o s n e r

Duana Fullwiley


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64 May - Jun e 2008

tionary history, gets reduced toracial or ethnic dierence, shesays, thats a big mistake.

Not all genetics projects are sopotentially divisive, however. InFebruary, Spencer Wells, Ph.D. 94, a for-mer Lewontin student, came to Harvardto tell a story of human connectedness.Wells, who heads the joint National Geo-graphic Society-IBM nonprofit Geno-graphic Project, spent an afternoon withstudent members of the Harvard Founda-

tion, which represents 72 student organi-zations from the Albanian Society to theVietnamese Society, says director S. AllenCounter. Wells had previously invited thestudents to participate in the Geno-graphic Project by sending in cheek swabswith their DNA for analysis. The idea,says Counter, was to show a diversegroup of students how they connect tothe rest of humanity.

Wells has created a human family treethat traces the journey of man (as he ti-tled his 2002 book) in populating the entireplanet from a homeland in Africa. The pro-

ject has used linguistic and genetic studiesto guide its sampling of indigenous popula-tions from around the globemany ofthem isolated and remoteand now hasthe worlds largest and most representativeanthropological database of human DNA.

At Harvard, a Pakistani-American stu-dent whose family had always told her theywere originally from an area near the Ara-bian Sea had this confirmed by her DNA re-sult. Your family was part of the first mi-

gration out of Africa,noted Wells. You sharethat with the Australianaborigines. An African-American student with an-

cestors from East Africacarried a genetic signaturecharacteristic of that re-gion. But an Asian-Ameri-can student was surprisedto find that she carried al-most the same geneticmarkers as a Mexican-American student. Wellsexplained, There is onlyone change, but you arefairly dierent becauseyour lines diverged a long

time ago. Still, you are partof the same branch of thetree: the Native Americanswho populated the West-ern Hemisphere originallycame from Asia.

The Genographic Project aims to tellpeople where their ancestors were livingas indigenous people at dierent pointsin time, but cant, for example, tell mostAfrican Americans precisely where inAfrica they are from because, Wells ex-plains, the database isnt quite there yet.

Echoing Fullwileys reservations about allsuch tests, he says hes a bit concerned

about some of the African-American DNAtesting companies purporting to trace youback to your ancient tribe. Ancestry isactually more complex for the averageAfrican American, he says, not only be-

cause people in West Africa (where mostof the slave trade occurred) have movedaround a lot in the last 500 years, but alsobecause group composition within Africahas changed over time. Furthermore, be-cause only a small number of humans sur-vived the journey out of Africa some

50,000 years ago (and the slave trade onthat continent was relatively localized),there is more diversity in the averageAfrican village, Wells notes, than thereis outside of Africa combined.

When asked about the question of race,Wellss answer was unequivocal. Racismis not only socially divisive, but also sci-entifically incorrect. We are all descen-dants of people who lived in Africa re-cently, he says. We are all Africans underthe skin. The kinds of dierences thatpeople notice, such as skin pigmentation,limb length, or other adaptations are ba-sically surface features that have been se-lected for in the environment. When youpeer beneath the surface at the underlyinglevel of genetic variation, we are all much

more similar than we appear to be. Thereare no clear, sharp delineations.

J O H N H A RVA R D S J O U R N A L

Ph o t o g ra p h b y R o m a n a Vy s a t o v a 2 0 0 8 N a t i o n a l G e o g r a p h i c

Spencer Wells tellsstudent volunteersof the HarvardFoundation about theirdeep ancestorsancient migrations.

Markers, Male and Female

Genetic tests have limits, even as tools for tracing ancient migrations. Becausemen dont move around as much as women do in patriarchal societiescontrary topopular belief, says Spencer Wells, Ph.D. 94, who heads the joint National GeographicSociety-IBM Genographic Projectthe Y chromosome is the best marker for chartingmigration patterns until it dead-ends about 60,000 to 90,000 years ago in one man wholived in Africa. To trace earlier migrations, scientists use mitochondrial DNA, whichpasses exclusively from mother to child. That trail leads back 200,000 years to onewoman. The striking dierence in the time frame, Wells notes, reflects the fact that, his-torically, most women have an opportunity to reproduce, but only a few men doand thus a more diverse sampling of the earliest female human lineages has survived.

Wells says genetic evidence tells us something about the who, the where, thewhen. But to make sense of the how and the why (which is the fun part), you haveto draw in archaeology, anthropology, paleoclimatology, linguisticsall these otherfields. Climate shifts have been an important factor, though not the only one: hesrecently turned up a genetic impact of the Crusades on the gene pool of the MiddleEast. We can actually trace Christian lineages in Lebanon back to source popula-tions in Europe, he says. That sort of resolution has never been possible before be-cause we didnt have a large enough sample size.


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