Though one country politically, the genetics of indigenous Mexicans shows that their ancestors were very distinct groups that mixed remarkably little. A study published today in Science found more genetic isolation than expected among these populations.

"You can clearly differentiate each of the native American groups one from the other," said Carlos Bustamante, a professor of genetics at Stanford who led the research. It was "kind of surprising," he said, that this "plays out even though there's been 500 years of admixture, huge amounts of population growth, and lots of migration and movement."

The study marks the first time that researchers looked at the genetic history of Mexico, taking samples from more than a thousand people representing 20 indigenous and