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Using DNA to trace people, past and present

Two stories in the news this week show how DNA analysis revolutionized our ability to identify people and trace their ancestry.

In Thursday’s New York Times, Amy Harmon reported on how police are using “surreptitious collection” of DNA samples to catch a suspect. A soda can offered during an interview; a dropped cigarette butt; even a drop of saliva from a suspect in the street, can provide enough DNA to link a suspect to a crime. In some cases, detectives have even used a ruse such as sending a suspect an invitation to join a class-action lawsuit so he would lick an envelope and return it to them.

But are such collections constitutional, or do they breach the Fourth Amendment?

“Police can take a DNA sample from anyone, anytime, for any reason without raising oversight by any court,” said Elizabeth E. Joh, a law professor at University of California, Davis, who studies the intersection of genetics and privacy law. “I don’t think a lot of people understand that.”

The U.S. Supreme Court has yet to rule on the issue, although lower courts have mostly upheld the position that such DNA collection does not differ from collecting fingerprints left at a scene or going through trash for evidence. Some legal experts, though, think that there are potential problems of invasion of privacy — your DNA sample could contain vastly more information about you than a fingerprint.

It might, for example, tell archaeologists of the far future where you came from. An international team of researchers announced this week that they had found evidence of human habitation in America more than 14,000 years ago, over a thousand years earlier than previously known, by looking at DNA from fossil human excrement in caves in Oregon.

Accumulating evidence shows that humans arrived in North America from Siberia well over 14,000 years ago, probably more like 20,000 years ago and possibly much earlier, according to David Perlman’s article in the San Francisco Chronicle. David Glenn Smith, a professor of anthropology at UC Davis who specializes in DNA and human ancestry, called it “a carefully designed and comprehensive genetic study.” Human settlement around the caves may have occurred 10,000 years before the fossils studied by the researchers, Smith said.

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