A Look at the Entire Human Past
Before the Dawn: Recovering the Lost History of Our
Ancestors. Nicholas Wade. vi + 312 pp. Penguin Press, 2006. $24.95.
A few weeks ago, I mailed in a cheek swab with a bit of my DNA to a
forensic genetics laboratory. A CD and printout came back showing me
the genetic contribution made to me by my ancestors for the last few
thousand years on both my mother's and my father's sides. Being able
to obtain this sort of information is one more thing that in the
21st century we have come to take for granted, like seeing the
latest NASA photos of Mars online or phoning home while on a cruise
to Antarctica. Companies have popped up that offer to analyze your
DNA and, using genetic markers that are unique to certain ethnic
groups, tell you the mysteries of your history. Many people who
thought they knew their family's history, who even had a family
Bible with generations of written records of parentage, have been
shocked to learn that despite having been raised to believe they
were white Americans, they are actually substantially
African-American or Native American, or vice versa. In my own case,
I learned that I have a good amount of Native American ancestry, of
which I had had no inkling. This is human history in action, its
effects as up close and personal as possible.
In Before the Dawn: Recovering the Lost History of Our
Ancestors, Nicholas Wade, a science writer for the New York
Times, has woven a detective story from three strands: the
human fossil record, archaeological findings and our increasingly
detailed understanding of humankind's genetic history. Researchers
are uncovering a record of ancestry and ethnicity stretching from
you and me all the way back to the people of the Neolithic, with
some startling results.
Before the Dawn is a popularized look at the latest efforts
to understand the entire human past, with an emphasis on the past
5,000 to 10,000 years. Thus this volume complements other recent
books that cover in greater detail the more ancient past—our
emergence from the ape lineage that produced us.
After routinely covering the very early steps of human
history—the discussion is largely limited to the evolution of
the human form—Wade dives into the great human dispersal of
early Homo sapiens across the planet. Scientists can trace
this diaspora using a variety of methods. Geneticists make use of
mitochondrial DNA. Unlike the better-known variety of DNA in the
nuclei of your cells, the DNA in mitochondria undergoes mutations at
such a high rate that small differences among recently divided
populations can be studied. Because mitochondrial DNA passes only
through the maternal line, we can trace direct maternal ancestors
back thousands of generations. Results from mitochondrial studies
first provided evidence in the 1980s that the genetic differences
among all modern humans are trifling. This finding was bolstered
more recently by studies of the evolution of the Y-chromosome. These
investigations have provided the male side of human history and have
largely corroborated the early mitochondrial findings. Studies using
these methods have shown, for instance, that Africans in Uganda who
have long claimed to be the children of an ancient Hebrew priest
actually are so, and that Thomas Jefferson's many living descendants
include some whose maternal line goes back to his slave and mistress
Sally Hemmings. And thousands of people, including me, have been
able to learn who our ancestors really were.
Wade deftly follows the genetic detective story across all the
continents and some 50,000 years of our history, explaining recent
findings about the peopling of Europe and, much later, the Americas.
He shows that the concept of a single diaspora is simplistic. People
have been migrating in repeated waves down through the millennia,
and Europe and every other populated continent has seen multiple
invasions and immigrations, the records for which are preserved in
every cell in our bodies.
Wade also addresses cultural factors in evolution. He spends two
chapters describing the work of historical linguists, who have tried
to corroborate the genetic record of population movements, with some success.
If there is a flaw in this tightly written, insightful book, it is
that Wade provides perhaps too many of the stock examples of human
evolution. In my view, he spends too much time and space attempting
to convince the reader that we did indeed evolve from apes (duh!)
and that our own social behavior and cognition have roots in the
deep human past. I say this only because I think readers would have
preferred to hear more about the discovery of such evolutionary
mile-markers as the wearing of clothes, the invention of
agriculture, the peopling of the Earth and so on. These are the whys
and wherefores of our existence. Before the Dawn provides
ample evidence that scientists are hard at work answering these and
many other questions about a subject that has long been the stuff of
myth and mystery.
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