Nearly two years ago now I wrote a column for Slate arguing that DNA genealogy tests were misleading people. Here's what I wrote:
From a practical point of view, that is the biggest problem with today's genetic genealogy tests. In many cases, they can't tell you what you don't already know. And unlike DNA fingerprinting tests with error rates of one in a billion or less, the chance of misidentifying ancestral groups in these genealogy tests may be 5 percent or higher. With this chance of error, the test won't be wrong about a full Native-American grandparent, but it might be wrong about a great-great grandparent. In addition, SNPs that separate central Africans from northern Europeans aren't nearly as good at separating Ethiopians from Arabs. So, in the test results of some African-Americans, European means Europe, while in others, it may mean East African, or Arab, or Indian. Depending on where his African ancestors came from, Gates' apparently European origins might lie somewhere else entirely.
Now, here's what I find today in the Times by writer Ron Nixon:
Mr. Gates says his concerns [about genealogical testing] date back to 2000, when a company told him his maternal ancestry could most likely be traced back to Egypt, probably to the Nubian ethnic group. Five years later, however, a test by a second company startled him. It concluded that his maternal ancestors were not Nubian or even African, but most likely European.
Why the completely different results? Mr. Gates said the first company never told him he had multiple genetic matches, most of them in Europe. "They told me what they thought I wanted to hear," Mr. Gates said.
It's entirely predictable from the samples and methods these companies are using. It's also a case where there are a lot of vested interests in being able to give people the results they want to hear. Nixon quotes Troy Duster:
"My concern is that the marketing is coming before the science," said Troy Duster, a professor of sociology at New York University who was an adviser on the Human Genome Project and an author of the Science editorial.
"People are making life-changing decisions based on these tests and may not be aware of the limitations," he added. "While I don't think any of the companies are deliberately misleading customers, they may have a financial incentive to tell people what they want to hear."
Don't make life-changing decisions based on these tests! They can't tell you what tribe your ancestors came from. Period. Mitochondrial lineages have widespread distributions across Africa, and are not -- in most cases -- limited to any small region. That's the science.
In the meantime, I have been hearing from a number of readers who have paid for the Genographic Project and are dissatisfied. I'm collecting these stories, as well as stories from people who are happy with the results. Feel free to send me an e-mail if you're in either group.