Elizabeth Warren says a DNA test proves she has a Native American ancestor, but it's not that simple. Here's what the results really show.

sen elizabeth warren dna test

Senator Elizabeth Warren released DNA test results Monday showing that she probably has some Native American heritage.
A geneticist at Stanford University who analyzed Warren's DNA said he has "very high confidence" in the test results.
DNA tests can't tell you anything about your ancestry with 100% certainty. Here's what they really do.

For years, Senator Elizabeth Warren has touted the fact that she's part Cherokee, expressing pride in her Native heritage.

President Donald Trump has routinely mocked that assertion, using the nickname "Pocahontas" for Warren. In a July rally, Trump even said that if she could prove, based on DNA testing, that she has Native American ancestors, then he would donate $1 million to the charity of Warren's choice.

On Monday, Warren answered that call.

"A famous geneticist analyzed my DNA and concluded that it contains Native American ancestry," Warren wrote on Twitter.

On a webpage connected to her reelection campaign in Massachusetts, she also posted a video and a detailed ancestry report from the lab of Stanford genetics professor and DNA-sequencing expert Carlos Bustamante.

"In the Senator's genome, we did find five segments of Native American ancestry with very high confidence where we believe the error rate is less than 1 in 1,000." Bustamante said in the video posted on Warren's site. He said those results suggest that Warren "absolutely" has a Native American ancestor.

What Warren's test tells us

Senator Warren has not responded to Business Insider's request for information about precisely how she conducted the test, but most genetic tests that US consumers use today rely on cheek swabs. Users collect a bit of saliva that way, then send the spit in for analysis.

Typically, more than half the cells in someone's spit can include viable, intact genomic data about that person. Blood samples tend to have more DNA data, but saliva can be a decent way to extract genomic data with considerably less pain.

The DNA tests that are available to consumers, such as 23andMe or AncestryDNA, zero in on hundreds of thousands of locations on a person's genome. By doing so, they can pinpoint spots that give scientists clues about who a person's relatives could be.

Bustamante's analysis seems to have been done in a similar way. Warren’s sample "contained information on 764,958 sites of genetic variation," according to the report. These are the special spots in Warren's genetic code that make her different from everyone else, since most human DNA (about 99.9%) is identical from person to person. That other 0.01% is responsible for our differences, from the color of our eyes to the pigment of our skin, and even our genetic predispositions for disease.

The scientists compared Warren's sample to others from the 1,000 Genomes Project Consortium, which sequenced the genomes of 2,504 people from 26 populations around the world. Warren's DNA was compared to 148 people's fully-sequenced genomes: 37 of those individuals were from Europe, 37 had Sub-Saharan African ancestry, 37 were from the Americas and had Native American ancestry, and 37 came from China.

When scientists compare genomes in this way, they're looking for meaningful patterns: signs that one person's DNA shares certain tell-tale markers with another. That's a sign that the individuals may be distantly related, but it's not proof that one person is necessarily related to another.

Warren's sample had a lot of markers that are common to European ancestry, and a few that are common to what the researchers think could be Native American ancestry. The reason Bustamante thinks Warren probably has a Native American ancestor is that some DNA segments in her sample matched with segments from people native to Mexico, Peru, and Colombia. Those similarities suggest Warren likely had a Native American relative about eight generations ago.

"The largest segment identified as having Native American ancestry is on chromosome 10," the researchers wrote. "This segment is clearly distinct from segments of European ancestry, and is strongly associated with Native American ancestry."

Why genetic testing is not a perfect science

mouth swab dna saliva test

Consumer DNA testing is rapidly taking off. Today, more than 12 million people have tested their spit, according to MIT Technology Review.

But the genetic-testing kits that many people are trying don't always give accurate results about their lineage. A 2018 study published in the journal Genetics in Medicine suggested that 40% of the differences in genes reported in direct-to-consumer DNA tests were due to testing errors (false positives).

The tests are also raising concerns about privacy. A study released last week estimates that 60% of white Americans — who are the biggest consumers of DNA testing services — could now be identified up to a "third cousin or closer" using available DNA test data. The authors of the study said that information could implicate more criminals like the Golden State Killer in coming years, if more investigators compare DNA evidence from crime scenes with publicly available genetic information that's tied to people's names. That technique probably couldn't be applied to minority groups, though, because scientists don't have as much data from those groups. In fact, for some ethnic groups like Native Americans, scientists have hardly any data at all.

In Warren's case, the test didn't conclusively say whether her DNA matches that of current Native American tribal populations in the US. The researchers said making that connection wouldn't be possible, since "Native American groups within the US have not chosen to participate in recent population genetics studies."

At least 95% of Warren's DNA is likely of European origin, according to the test.

Should DNA decide who gets to be considered Native American?

In an article published in the Native Voice in 2004, racial politics professor Kim TallBear (a member of the Sisseton Wahpeton Oyate of South Dakota) and biological anthropologist Deborah Bolnick pointed out that "eligibility for Native American rights is ultimately a political and cultural issue that will never be satisfactorily answered by genetics."

So although Trump may have suggested that Warren should prove her background using a DNA test, native groups certainly didn't ask her to. In fact, the Cherokee Nation sent a statement to the Oklahoman voicing the group's disapproval.

"Current DNA tests do not even distinguish whether a person's ancestors were indigenous to North or South America," Cherokee Nation Secretary of State Chuck Hoskin Jr. said. "It makes a mockery out of DNA tests and its legitimate uses while also dishonoring legitimate tribal governments and their citizens."

Warren is not a tribal citizen, a fact she readily acknowledges on her website. For that, most US tribes require a "blood quantum" of one-quarter, which Warren most likely doesn't have (or purport to have).

Plus, as TallBear has said, nobody should be boiled down to the chromosomes in a spit sample, anyway.

"I worry about the way Native American identity gets represented as this purely racial category by some of the companies marketing these tests," she told New Scientist in 2014. "The story is so much more complicated than that."

For her part, Warren tweeted at Trump on Monday, asking him to send a $1 million check to the National Indigenous Women’s Resource Center, a nonprofit that works to curb domestic violence and improve the safety and well-being of native women. A 2007 report from Amnesty International found that Native women were 2.5 times more likely to be the victims of rape or sexual violence than other women in the US, and that nearly 86% of the rapes were committed by non-Native men.

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