Race and ethnicity have played an enormous role in American history. If the country is an assimilated melting pot of immigrants, it is also a nation of people who proudly associate themselves with particular racial or ethnic groups, from aristocratic European "blue bloods" to Italians, Jews, Arabs and Irish, and from African-Americans and Mexican-Americans to Asian-Americans and Native Americans. Most of those associations are based on physical appearance, limited direct knowledge of family ties, and some basic (but not necessarily true) assumptions about parentage.





The descendant of black slaves is assumed to be African American. The descendant of white slave owners, on the other hand, is assumed to be white/Caucasian/European ... and, in some camps, is also assumed to be superior because of that identity. Anyone who doubts the importance of racial and ethnic identity in American society and politics need look no further than the 2008 Presidential election for evidence to the contrary. Barack Obama was black. Not black. Too black. Not black enough. The efforts to assign him to a group--or, in turn, to deny him membership--because of his multi-racial heritage, lasted well beyond election day.





But with the advent of DNA testing, some surprising and unsettling truths are emerging--as the PBS series "Faces of America," which aired its final episode Wednesday night, made abundantly clear. Hosted by Harvard professor Henry Louis Gates, the last episode this week did DNA testing of 12 celebrities, from actress Eva Longoria and Queen Noor of Jordan to cellist Yo-Yo Ma and comedian Stephen Colbert, to see what their heritage really was.





One set of results showed some surprising relationships among the 12. Who knew that Stephen Colbert and Yale professor and poet Elizabeth Alexander were distant cousins? Same goes for Yo-Yo Ma and Eva Longoria. Gates also found that Dr. Mehmet Oz, the child of Turkish Muslims, shared a common ancestor, several centuries ago, with director Mike Nichols, a descendant of Russian and German Jews. Food for thought, in terms of Middle-East relations.





But the testing also uncovered some surprising truths about the ethnic heritage of those involved. Gates himself discovered that despite how heavily he identifies with his African American heritage, he's actually much more European than African. (Ironically, it was returning from a trip to China researching Yo-Yo Ma's ancestry for this show that Gates was arrested in Cambridge, sparking a highly charged debate about race in current-day America.).





Eva Longoria, who has always identified herself as Mexican, discovered that she's actually 70% European, 3% African, and only 27% Asian (which is the ethnic group under which indigenous Americans are classified). Elizabeth Alexander, who also discovered that she's a direct descendant of Charlemagne and King John I of England (on the wrong side of the blanket), found out that her "African American" heritage accounts for only 27% of her DNA. Sixty-six percent is European, and 7% is Asian.





What does all that mean? For one thing, there was evidently a lot more mixing of races in the history of the world than socially acceptable family trees and history would like us to believe.





"If all of us were only known by our DNA, then we'd have a whole different American history," concluded Alexander.





Indeed. The whole concept of the "other," and attendant stereotypes of what that ethnic association meant, would have been a whole lot harder to maintain if the DNA truth of many people's mixed-race heritage had been public knowledge 100 or 150 years ago. It would even rock some people's worlds to have to recognize it today. And not only because of unexpected racial or ethnic mixing with minority groups, but also, in some cases, because of unexpected ties outside of a cherished minority identity.





The element of the last PBS episode I found most intriguing was Gates' interview with novelist Louise Erdrich, who declined to have her DNA tested because her identity as a descendant of the Chippewa Native American tribe is so important to her. She said that she felt her tribe and family were what made her who she was. And, as she explained to Gates, she "didn't want to add any confusion to it."





Erdrich, in other words, didn't want cold, scientific facts to confuse her cherished notion of who she was, based on her assumed heritage. The same discomfort would probably be felt by any number of people who have built an identity based on a pure "white" bloodline that, if put under the DNA microscope, might prove to be something more mottled in nature.





Where does the line lie between healthy pride in a history and heritage and overzealous association with a particular narrative of our past? Perhaps it lies in the moment we turn away from the rich tapestry our DNA might reveal.





It's often said that we need to know where we come from to know where we are going. That was the genesis of the whole "Roots" movement. But as the miracle of DNA is showing once again, truth is generally messier than fantasy. If we are really honest in saying we want to know where we came from, then we have to be willing to embrace whatever the answer is. Even if, as Yo-Yo Ma said, the fact remains that, regardless of who your ancestors may have been, you still need to define and prove yourself here and now.





But, still. Barack Obama's candidacy and election sparked endless discussion about whether this meant we finally had achieved a "post-racial" society, where we could transcend racial boundaries and stereotypes. What the DNA testing in PBS's "Faces of America" showed was that ... at least beneath surface appearances ... we've been post-racial for centuries. We just didn't know it.