E10. Can DNA Tell What "Race" You Are?


Uploaded by frankwsweet on 02.11.2010

Transcript:
Karen: Welcome, ladies and gentlemen. This is Karen Sharpe with another session
in our series of discussions on the study of racialism, with Professor Randolph Hemmings.
Good afternoon, professor, I am sure that the viewers are looking forward to today's
topic. Professor Hemmings: Thankl you Karen, I'm
glad to be here. People love to classify one another.
Are you a Christian? A liberal? A college graduate? An Argentinean? A White man?
All of us routinely classify others in hundreds of different ways.
And many of our classification schemes overlap or even contradict each other.
Today we consider two popular ways of classifying people and the link between them.
One system groups people into populations that can be genetically identified by markers
in their DNA. The other method divides people into? socially
identified races. If you do not know better, you might expect
these two methods to match more or less. Not so.
Molecular anthropologists are often asked if DNA markers can tell what "race" you are.
The short answer is "no." Mitochondrial DNA, and Y haplogroups, can
tell from which continent, your matrilineal and patrilineal ancestors came.
And if you live in the Americas, autosomal mapping can tell what fraction of your ancestors
came from Africa as slaves, what fraction came from Europe as colonists, and what fraction
were Native Americans. But no DNA can tell your race in society.
Oddly, there is no contradiction between saying, "DNA cannot tell what race you are," and saying,
"DNA can tell where your ancestors came from." Let's see why.
Consider identifiable populations. To a molecular anthropologist, there are thousands
of genetically identifiable populations on earth.
Scientists no longer call them races. Mainly, because there are so many of them.
There are dozens of such populations in Europe and hundreds of them in Africa.
Indeed, there are more distinct populations in Africa than around the rest of the globe
combined. There are three ways of using DNA to study
the history of human populations: mitochondrial or mtDNA, Y chromosome or Y DNA, and autosomal
or admixture DNA. Only the third approximates social classification
by race, and this is by design. Let's look at each.
Mitochondrial markers (mtDNA haplogroups) were discovered earliest and have been well
studied. Everyone carries them.
They descend through the maternal line, passing from mother to daughter.
Men get theirs from their mothers but cannot pass them on.
They remind you of the clan system of the Native American tribes of the U.S. southeast,
so mtDNA haplogroups are often called clans. The map shows prehistoric migrations of mothers.
Over tens of thousands of years, they carried the different mtDNA markers around the globe.
Here are three examples: If your mtDNA is haplotype H, then you descend from mammoth
hunters, who moved into Europe about 45 thousand years ago.
If your mtDNA is haplotype B, then you either descend from Native Americans, or from their
ancestors who remained in Asia about 22 thousand years ago.
And if your mtDNA is haplotype L3, then you descend from east Africans.
But mitochondrial DNA, mtDNA, tells little about your own make-up.
Ten generations ago (around the year 1800) you had a thousand ancestors, only one of
whom (your mother's mother's mother and so forth) had that particular mtDNA.
Your other 999 ancestors might all have had totally different ancestry.
For example, my own mtDNA is type A. In other words, Native American.
And yet, I am northern European in appearance and my family has no tradition of having any
Native American ancestry at all. Y DNA is patrilineal.
Y chromsome markers (Y haplogroups) were more recently discovered but are also well understood.
Only males carry them. They descend through the paternal line, passing
from father to son. It reminds you of the way surnames work in
the Western world. And so, Y haplogroups are often used by genealogists
pursuing surname ancestry. The map shows prehistoric migrations of fathers,
who, over the past tens of thousands of years, carried the different Y markers around the
globe. If your Y is "R1b" then your ancestors arrived
in Europe before the ice ages. If your Y is "Q," then you either descend
from Native Americans or from their ancestors who remained in Asia.
If your Y is any E, other than E 3 b, then you descend from west Africans.
Why does this not tell your "race"? Again, it is because only one man, out of
your 1000 ancestors, in the year 1800, carried your own particular Y haplogroup marker.
The other 999 ancestors might have had totally different ancestry.
For example, my own Y is of type R1*, from Cameroon in west Africa.
And yet, as I already mentioned, I have a northern European appearance, and no credible
family tradition of sub-Saharan ancestry. Hence, the "race," that most people see in
me, matches neither my mtDNA nor my Y haplotype. Now let's look at autosomal markers.
Autosomal markers reveal percentages. These DNA markers are different from mtDNA
or Y chromosome haplogroups, in that they measure the average continent of ancestry
admixture, scattered throughout your entire genome.
The technique of autosomal admixture mapping is more recent than either mtDNA or Y, and
it is still being refined. It was originally devised for New World inhabitants,
to measure what fraction of their ancestry came from each of the three demographic sources:
Africa, Europe, and Native America. Autosomal mapping comes closer to identifying
"race" than the other two techniques. This is because the method was devised to
satisfy curiosity as to the extent of genetic mixing in the New World, from among the three
demographic sources. And, since social race is associated with
continent of ancestry, autosomal admixture mapping, resembles racial classification.
For instance, with a couple of exceptions, if your autosomal DNA admixture is overwhelmingly
of European origin, you are likely to be seen as White in America.
And in America, if it is of mostly African origin you will probably be considered Black.
But there are two major exceptions to this rule, and one minor exception.
The first major exception is that many members of the African American community are of overwhelmingly
European admixture, and yet consider themselves Black nonetheless.
In the United States, Black, or African American, is partly a voluntary ethno-political self-identity.
In fact, about 5 percent of self-labeled African Americans have no detectable African admixture
at all. The second major exception is among so-called
Hispanics. The autosomal admixture of people from Latin
America is a widely variable mix of all three sources.
And yet, most of them consider themselves all to be of the same ethnicity.
For example, my own autosomal admixture is 13 percent African, 12 percent American Indian,
and 75 percent European. Curiously, my personal admixture almost exactly
matches the demographic average admixture percentages found in the inhabitants of Puerto
Rico. The final, minor exception, where admixture
does not match social race, is that some individuals of mixed ancestry
happen to inherit those genes for racially-perceived external appearance,
but not the invisible auto zomal markers. It is rare, but it does happen, that someone
who looks White, carries significant African markers, or vice-versa.
In conclusion, neither mtDNA nor Y DNA can give any hint as to your "racial" membership
in U.S. society. Autosomal DNA, if very lopsided to one continent
or another, can suggest what you look like. But this does not work for those Americans
who choose to self-identify as Black despite having mostly European DNA,
nor for White Americans unaware of their African DNA,
nor for Hispanics, whose "racial" membership is determined by their culture, not by their
genes. Thanks for listening.
I shall now entertain questions. Karen: Thank you professor.
I must say, I am ever more astonished every time that you talk about America.
The idea that people with little or no real African ancestry consider themselves Black
is very strange. Are there no mixed or coloured people in the
United States? Professor Hemmings: Very few.
Long ago, in the early 19th century along the gulf coast, Americans of mixed ancestry
had legal recognition, and enjoyed intermediate social status.
But as the United States became unified into a single culture after the Civil War, the
in-between category was legally abolished. Although some activists today are trying to
change things, multiracial americans nowadays have no legal existence.
Every American citizen must choose to be either wholly white or totally Black, no in-between
allowed. Karen: Amazing.
Professor Hemmings: Did we get any viewer questions?
Karen: You might not consider most of the calls to be questions.
Several people insisted, rather vehemently, that you got it all wrong.
Some said that there are only four races: white black red and yellow.
Others said that there were many races, but that they were determined by patrilineal ancestry.
They said that inheritance through the female is irrelevant to race.
Others said the opposite, that only females can transmit race.
Professor Hemmings: As you implied, those were not questions.
One of the odd things about the race notion, is that we learn the concept in early childhood
from our parents, at about the same time that we learn to talk.
And so, it is thoroughly internalized, like our native language is internalized.
Most people are sincerely convinced that they know, with unshakeable certainty, how many
races there are, and who is of which race. But of course, they do not agree with each
other. To each individual, everyone else is wrong.
We talk about this phenomenon in depth, in our session on the perception of racial traits.
Karen: An American forensic anthropologist said that racial classification is precisely
defined under U.S. law. Legally speaking, there is no doubt nor ambiguity
as to which American is of which race. Professor Hemmings: That is correct.
Racial classification is taken very seriously in U.S. law.
The decennial census demands that you choose a "race."
Every employer that you might work for, every school that you might attend, every government
social service that you might request, demands that you choose a race.
Every organization is then required by regulations to report your choice to the federal authorities.
Furthermore, if someone disputes your choice, you can be accused of fraud, your true race
will be decided by the court. Why is the U.S. government so serious about
knowing your "race"? Because U.S. voters are serious about it,
and have been since 1705, when the first statutes were passed defining how many "races" there
were, and who belonged to each one. Why do U.S. voters demand this?
The most common reason given, for demanding that everyone publicly choose a "race," under
penalty of law, is that only thus can the nation fight racism.
Some disagree. They argue that forcing every American to
swear allegiance to a race, merely exacerbates racism.
Others argue that compulsory racial identity does not go far enough.
They say that the federal government should also demand that everyone admit their religion,
on school applications and on job applications, in order to better fight religious prejudice.
As does the government of Trinidad and Tobago, for example.
And a few argue that your political affiliation should also be reported on job applications,
and school applications, in order to fight political prejudice.
But most Americans feel that being forced to choose a religion would go too far, while
letting people get away with not choosing a "race" would not go far enough.
Karen: One last question from a woman in Italy. If race is merely a social construct, then
how can DNA admixture mapping tell your continent of ancestry?
Professor Hemmings: Because that is how those particular markers were selected.
Look at it this way. Some auto zomal markers tell whether your
ancestors cultivated grain or herded animals. Others tell, whether your ancestors lived
in the mountains or on the sea shore. And still others tell, whether your ancestors
lived in cold or hot climates. Continent of ancestry markers are no more
fundamental than any others. They are more popular, simply because people
are more interested in continent of ancestry, than in herding versus agriculture.
Karen: Thank you professor. Well folks, that is our time for today.
Next week, professor randolph hemmings will discuss The U.S. one-drop rule.
For now, this is Karen Sharpe signing off.