Because African-Americans and European-Americans have been in contact, sometimes intimate, since 1619, these questions are central to Americans' collective self-understanding. In recent years, genetic techniques for accurately determining the answers have finally become available.
Molecular anthropologist Mark D. Shriver heads a group of nine population researchers at Penn State University who are going beyond the arbitrary "one drop of blood" rule to answer these ancient questions about the family trees of the typical American "black" and "white."
They have examined DNA samples from 3,000 individuals in 25 locations around America, mostly self-identified African-Americans, looking for the gene markers that tend to differ between Europeans and Africans.
Shriver pointed out that genetically tracking admixture is difficult because differences even between subraces, such as Scandinavian versus West African, account for only about ten percent of human genetic variation. "Thus, we are all more alike than we are different," he noted.
Besides illuminating American history, Shriver hopes to use his ability to determine racial admixture to locate genes associated with illnesses that affect one race more than the other -- such as diabetes, prostate cancer, and hypertension, which are more prevalent among African-Americans, and dementia and osteoporosis among whites.
To Shriver, the most personally stunning of his findings involved one subject who reported himself to be completely white, yet whose genetic analysis showed that 22 percent of his relatively recent ancestors were African.
"I had the result for two or three years before I even looked up the ID number of the person whom we tested," a bemused Shriver recounted. "I looked at who it was and it was me! I checked myself and the rest of my relatives and tracked it through my family."
"I never considered that there were any African people in my family," remarked the 36-year-old Shriver, who looks like a typical white American. He has wavy brown hair and light skin that burns easily, but also tans darkly.
His siblings look completely European, too. "There's no real variation in my family. The admixture must have been pretty far back. It just so happens that we can detect it with the markers we have."
"My mom especially stood out as being surprised, maybe because I told her it was coming through her father." He credits his Catholic parents with providing him with a "balanced, open, and egalitarian perspective about people. But, still, she doesn't believe it about her family!"
"The part of Pennsylvania where my mother's father came from is where the Underground Railroad ended," Shriver observed, referring to the network that smuggled escaped slaves north to freedom. "There are several towns right here in Southern Pennsylvania where there are very light-skinned African-American communities that are the remnant of the Underground Railroad."
His maternal grandfather moved from Pennsylvania to Iowa, then to California, leaving behind in the process most of his ties with his relatives. Shriver is considering trying to track down his maternal grandfather's relations in Pennsylvania.
The subject of black-white admixture is particularly complicated because, since the later 17th Century, Americans with virtually any visible sub-Saharan African ancestry (the so-called "one drop of blood") have been socially categorized as simply African. Only recently has society begun to tolerate individuals like Tiger Woods (who is one-half East Asian, one-quarter sub-Saharan African, one-eighth European, and one-eighth Native American) defining themselves as anything other than as African. Indeed, Woods was criticized by some African-Americans in 1997, following the first of his three Masters' victories, for not submitting to the "one drop" definition.
Is Shriver's ancestry fairly typical for an American? In two ways, it is. First, more than 50 million whites, according to his analyses, have at least one black ancestor.
Another way to approach the question is to group together all the whites and blacks in America and calculate their mean degree of admixture. Shriver's data shows that on average, they would be about 12 or 13 percent African. So, Shriver, at 22 percent African, is fairly close to the mean.
Yet, from another perspective, Shriver is highly unusual. Even though his family tree is similar in its racial balance to the theoretical mean for blacks and whites combined, there simply aren't many African-Americans or European-Americans with anywhere near his level of admixture. Shriver pointed out, "There is a very small degree of overlap in the population distributions." In America, most of the whites are extremely European and most of the blacks are quite African.
Despite the notorious arbitrariness of the "one drop" rule, the actual American population conforms to its strictures surprisingly closely.
Granted, the "one drop" rule would be laughed out of existence if anyone attempted to impose it on a land with a more genetically blended population, such as Puerto Rico (which Shriver has begun to study). Yet, it appears possible that the rule survives in the U.S. because it's not too wildly inaccurate. Only a small fraction of the population resembles Shriver in being more than half, but less than 90 percent European.
Among self-identified whites in Shriver's sample, the average black admixture is only 0.7 percent. That's the equivalent of having among your 128 great-great-great-great-great-grandparents (who lived around two centuries ago), 127 whites and one black.
It appears that 70 percent of whites have no African ancestors. Among the 30 percent who do, the black admixture is around 2.3 percent, which would be like having about three black ancestors out of those 128.
In contrast, African-Americans are much more racially mixed than European-Americans. Yet, Shriver's study shows that they are less European that was previously believed.
Earlier, cruder studies, done before direct genetic testing was feasible, suggested that African-Americans were 25 or even 30 percent white. Shriver's project is not complete, but with data from 25 sites already in, he is coming up with 17-18 percent white ancestry among African-Americans. That's the equivalent of 106 of those 128 of your ancestors from seven generations ago having been Africans and 22 Europeans.
According to Shriver, only about 10 percent of African-Americans are over 50 percent white.
This genetic database is restricted to adults. Black-white married couples quadrupled in number between the 1960 Census and 1990 Census, so the admixture rates among children are no doubt higher than among adults.
Political conservatives have taken to denouncing the "one drop" rule -- George Will recently called it "Probably the most pernicious idea ever to gain general acceptance in America" -- perhaps because it is used to determine who qualifies for affirmative action for blacks. Many opponents of racial preferences now argue that it is absurd to award benefits based on this arbitrary definition. This view is embodied in Ward Connerly's upcoming Racial Privacy Initiative, which would partially ban the state of California from demanding citizens categorize themselves by race.
The number of mostly white but a little-bit-black young people -- the kind who cause confusion for affirmative action classification schemes -- is growing as interracial marriage becomes more popular. On the other hand, as Shriver's data shows, there aren't yet all that many adults who fall genetically in the "gray zone" between the races. Perhaps at present the "one drop" rule, for all its theoretical folly, still is indeed good enough for government work -- assuming that government work should include racial preferences, which are now illegal in California.
The admixture rates vary by region. The African-American populations with the highest average numbers of white ancestors found so far are those in California and Seattle. They average a little over one-quarter European ancestry.
In contrast, according to a recent article published by Shriver's team in the American Journal of Physical Anthropology, the Gullahs of the long-isolated Sea Islands of South Carolina and Georgia, who are famous for speaking a pleasantly African-sounding dialect, are only 3-4 percent white.
In the rest of the rural South, African-Americans tend to be not as black as the Gullahs, but still blacker than the national average. Shriver's team found that the white admixture percentage in four Lowland farm counties in South Carolina was 12 percent.
Cities, whether Northern or Southern, tend to be about average. In terms of white ancestry among African-Americans, New York is a little above the mean, while Philadelphia is a little below. Jackson, Miss., is near the norm.
The African-Americans of New Orleans average 22 percent white. This fairly high number reflects the influence of Spanish and French mores in Louisiana. Latin cultures have no "one drop" rule, so intermarriage was somewhat more socially acceptable there.
Advocates of the growing popular idea that race is merely a "social construct" with no biological reality point to the artificiality of the "one drop" rule as evidence for their view. Yet, it's possible that the "one drop" rule itself helped to construct the genetic reality that Shriver has uncovered.
Latin cultures, which lack the one drop rule, create more evenly blended populations, as Shriver has helped document among Mexican-Americans. He and his colleagues found that Hispanics in certain New Mexico and Colorado locales averaged 58 percent white ancestry, 39 percent New World Indian, and three percent African.
In contrast to the "bimodal distribution" of blacks and whites in America, Mexican-Americans clustered around their average admixture level of 58 percent European.
For centuries, however, American whites defined anyone with visible black ancestry as ineligible to marry a white. (It wasn't until 1967 that the Supreme Court overturned the "anti-miscegenation" laws that were then still in force in 19 states.) This meant that mixed race people could seldom marry white people.
Unless, that is, they were white-looking enough to pass for white, and were willing to pull up their roots and move to a different part of the country where they could assume a white identity. This happened not infrequently in American history. For instance, one of the slave Sally Hemmings' one-eighth black sons (who, according to geneticists, was fathered by either Thomas Jefferson or one of his relations) moved to Madison, Wis., after he was freed and founded a family of socially identified whites. Nonetheless, Shriver's data suggests that well over 90 percent of the African genes in Americans are still found in people who call themselves black.
Over the generations, mixed-race lineages would tend to either pass into the white population and become more white with each generation's marriage to a white person, or stay in the African-American population. If the latter, the families would normally become more genetically African over time as their offspring married African-Americans.
Thus, the "one drop" rule helped make African-Americans and European-Americans into two social groups whose members -- despite sometimes being highly varied in ancestry -- are perhaps more distinct on average in their family trees than the arbitrariness of the "one drop" would lead you to initially assume.
In the final article in the series: What happened to the Africans of Mexico?