Writers, artists and historians have long pondered what it means to be Mexican. Now science has offered its answer, and it could change how medicine uses racial and ethnic categories to assess disease risk, testing and treatment.
The broadest analysis of the Mexican genome ever undertaken reveals a nation of staggering genetic diversity, where European conquest only thinly masks the ancestral DNA of Native Americans, and where some populations remain as distinct from one another as Europeans are from Chinese, according to findings published Thursday in the journal Science.
Forty researchers, who share Latino heritage as well as professional qualms over the significance of ethnic and racial categories, teamed up across borders to analyze more than 1 million variations in the building blocks of DNA. They examined more than 500 samples collected in Mexicos remote Indian villages and polyglot cities, and from Mexican Americans in California.
Because these populations are so rich, so genetically differentiated, you cant just lump them all in, said lead investigator Carlos Bustamante, a population geneticist and co-director of Stanford Universitys Center for Computational, Evolutionary and Human Genomics. You really have to embrace that diversity and think about doing medical genetic studies on a very large scale.
To illustrate their point, the researchers compared their new genetic data with the results of lung function tests for children in Mexico City and Latinos in the San Francisco Bay Area. They discovered that pulmonary function varied in ways that were mirrored in DNA. It was as if someone with a fraction of Maya ancestry had lungs that were 10 years older than someone with a bit of northern indigenous heritage.
Those results could affect how doctors define normal ranges on such tests, and thus diagnoses and treatment for common conditions such as asthma and pulmonary obstruction, said Dr. Esteban Gonzalez Burchard, a UC San Francisco asthma researcher and one of the studys coauthors.
Were pushing the ball down the field toward precision medicine, he said. We actually just care about what your ancestry is at a particular gene.
Indeed, it turns out that the genetic meaning of Mexican is quite complicated. The variation among indigenous populations, for instance, gets sharper by distance a gradient that runs roughly parallel to Mexicos northwest-to-southeast mountain ranges. So a Seri from the Gulf of California area varies as much from a Lacandon Maya near Guatemala as a white person does from an Asian, researchers found.
But Mexico is a land of mixture, captured in the term mestizo that describes someone of European and Native American heritage. The researchers wondered whether the genetic signature of the Aztec, Maya and other cultures had been overwhelmed by the genes of the Spanish conquistadors over the course of the last half millennium.
They were shocked to find that the indigenous component of mestizo samples replicated the same geographic differences found in the indigenous samples. Conquest had not swamped the genetic signal of ancient Mexico.
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Mexico boasts a staggering genetic diversity, study shows