Our genes are both new and old -- remade fresh in every copy of a cell,
but carrying bits of information
handed down from the birth of human history.
While the field of genetics has been used for decades to study our past,
tools of the modern molecular
biology revolution offer a far more precise way to trace the regional origins of subsets of humans -- and
follow our ancestors in their 150,000-year-long journey around the globe. Because genetic material is
passed down from parents to children, it creates a road map of our past.
Author Steven Olson has undertaken the task of tracing that map. In his
new book ``Mapping
History,'' Olson assembles the vast collection of genetic studies to create a colorful narrative of human
migration over time.
Olson, a writer based in Washington, D.C., has written reports for everyone
from the National Academy
of Sciences to the White House Office of Science and Technology Policy and the Institute for Genomic
Research. He interviewed dozens of scholars around the world in his research for the book.
He calls human DNA ``a virtually limitless repository not just of biomedical
but of historical information,
a sort of molecular parchment on which an account of our species has been written.''
In the Bay Area recently to give a reading, Olson discussed who we are -- and where we came from.
Q Those of us who studied genetics in high school biology tend to think
of it as something dry and fairly
technical. In your book, it becomes a tale of sex and death, adventure and travel.
A It's very exciting compared to what we learned in school. For hundreds
of years, people have asked
where the differences between human groups came from. What I found amazing, in writing this book,
is that the answers have just begun to emerge in the past few years through the study of the genetic
differences between people.
Q What is the role of genetics in understanding our past?
A The only way to understand our genetic similarities is to understand
our differences. Everyone on
Earth has a unique set of the chemical subunits that make up his or her DNA. We got these genetic
sequences from our biological mother and father, and they got them from their parents, and so on back
through time. These differences in our DNA are a link between generations. They record who had
children with whom all the way back through human history. So we can use them to put together a
gigantic family tree of our species.
Q What does genetics tell us that linguistic history and archaeology can't?
A Linguistic and archaeological evidence is part of the overall story,
but only with this new genetic
information can we put together a complete narrative of the thousands of years of human history.
Traditional archaeology left many questions unanswered that the genetic evidence can help answer --
such as whether anatomically modern humans originated at a single place and time or whether our
origins have a more complex history. So far, the genetic evidence argues strongly for a single origin of
modern humans, followed by expansion into the rest of the world.
Q Are there any historical narratives that you found were unsupported by genetic data?
A Our genetic history demonstrates that reality is much more complex and
interesting than many
stories might indicate. For example, these stories often suggest that groups of people have separate
biological histories. Genetics shows that our separateness is an illusion -- we are much more closely
related than we thought.
For example, Jewish populations have existed as cultural entities for more
than 3,000 years, yet they
have very close ties, genetically, to the populations within which they have lived. There is a long history
of people coming into Judaism and leaving Judaism. All ethnic groups have mixed with others.
Q We have a propensity to sort people into categories. Previous attempts
at so-called ``racial science''
brought so many terrible things, and we accept now that genetic analysis of racial differences is
unfounded. Yet in the field of genetics, it is all about the study of small differences between groups of
people. And this is seen as good. What's the difference?
A This research has the potential to create a much deeper understanding
of what we mean when we
use terms like ``race'' or ``ethnic group.''
Everyone has a unique biologic history; every group has a unique biologic
history. But our histories are
so complicated and overlap so extensively that it is misleading to try to capture those histories with a
simple term such as ``race.'' Humans just can't be sorted into discrete categories. We use the word
``race'' to mean ``a person or group with a particular set of external physical appearances who lives
in a particular part of the world.'' That's fine, but it doesn't have much to do with our genes.
Q So there is a spectrum of human diversity?
A It is even more complicated than a spectrum. A spectrum implies a linear
scale, going from one end to
the other. It's more like a highly interconnected network. It's not two-dimensional. It's not
Q If groups overlap genetically, to what extent can you or I or a Spaniard
or a Native American Indian
be defined genetically? Can genetics be used to assign an individual to a group?
A It is impossible to define any one of those groups genetically. The most
you can say is that,
statistically, this group has a higher percentage of a particular genetic marker than another group. But
you will never find a genetic marker that is 100 percent present in one group or 100 percent absent in
another. You will always run into problems when you try to use a biological indicator, like a genetic
variant, to assign people to a cultural entity.
Q But you can use genes to trace ancestry?
A Yes, you can use biological indicators to reconstruct ancestry. These
ancestries are very complicated,
and they overlap, but we all do have our own biological histories.
Q Your book says that ``we differ in the most superficial ways,'' that
cultural differences do not have
biological origins. Yet everyone noticed how Africans swept the Olympic running events, how Russians
excel at chess, how Italians are thought to be emotionally volatile while Swedes are cool. Are these
differences all cultural?
A Given our biologically interconnected history, you would expect almost
all differences among human
groups to be exclusively cultural. It is very difficult, using biology, to explain how these groups would
come to have these different kinds of advantages.
Of course, our bodies are somewhat different on the outside because of
the environments in which our
ancestors lived. Perhaps you're from a population that lived at high elevations, so you'll be better at
climbing Mount Everest than I would be.
But given the similarities in our genetic history, social and cultural
factors have to be the main forces
driving groups in different directions. Yet biology tends to be the first thing people look at. Maybe that's
because our physical appearances are so obvious in humans, we're trained to look at them first.
Q One of the other interesting observations in your book is that the movement
of our ancestors was
not unidirectional -- simply from south to north, or from east to west. People, and generations, seem to
travel in many different directions.
A We know that anatomically modern humans arose in eastern Africa about
130,000 years ago. And
the short version of the story is that they spread from there all over the rest of the world. But these
movements were not in one direction. People have always moved in both directions and sideways as
Q Human migration, it seems, is sometimes related to technological change
but also quirks of history,
culture and geography.
A Yes. For instance, every European population thinks of itself as a distinct
group, but it's really an
amalgamation of many pre-existing groups that came together in the past.
In the book, I focused on France because so many different genetic contributions
can be seen there.
We think of the French as representing a biologically distinct group of people, but when you look at
their genes you see evidence of the many different populations that have occupied the region at
different times. You see farmers who came out of the Middle East with the development of agriculture
10,000 years ago. You see northern Europeans like the Vikings and Franks. You see Roman and Greek
settlers coming along the Mediterranean coast. And those are just the larger groups. Many smaller
groups have mixed in France as well.
Q Given the trend toward mixing and assimilation of populations, do you
homogeneity in the United States and the world?
A Not necessarily. The forces leading to homogeneity can exist at the same
time as forces that oppose
it. Some parts of the world already have great cultural uniformity. In other places, such as parts of
Europe, the mixing of cultures is causing great social upheaval and political change. And even in places
where there is a great mixing of people, homogeneity is not inevitable. Immigrants don't automatically
adopt the culture around them -- they bring their own cultural influences.
Q Have we arrived at a point where there is a synthesis of archaeology,
linguistics and genetics which,
when combined, will provide a complete picture of human pre-history?
A We're not there yet, and it's hard to predict when this much-anticipated
synthesis will occur. But
progress could occur quickly, because the biomedical community is now collecting fantastic quantities of
genetic information. Researchers are trying to understand how different people respond to medical
treatments, although it remains to be seen how much of a difference in response there will be.
But regardless of what we learn on the medical front, this research is
going to produce a vastly
expanded understanding of our history.
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