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From: "K S Harris" <>
Subject: [yDNAhgI] New Scientific American article: Traces of a Distant Past
Date: Mon, 16 Jun 2008 21:26:11 -0700


[If anyone wants the entire article, I can send directly -- Group policy
won't permit articles of this length]


*Title:* Traces of a DISTANT PAST. (cover story)*Authors:* Stix, Gary*
Source:* Scientific American; Jul2008, Vol. 299 Issue 1, p56-63, 8p, 2
diagrams, 6 graphs, 2 maps, 7 color
***Abstract:* The article discusses advances in population genetics that are
allowing scientists to trace the path of human migrations out of Africa by
testing the DNA of existing indigenous populations. Recent genome studies
examining genetic markers in the Y chromosomes of men from around the world
have produced maps of the routes of ancient human movements.
KEY CONCEPTS

• Scientists trace the path of human migrations by using bones, artifacts
and DNA. Ancient objects, however, are hard to find.

• DNA from contemporary humans can be compared to determine how long an
indigenous population has lived in a region.

• The latest studies survey swathes of entire genomes and produce maps of
human movements across much of the world. They also describe how people's
genes have adapted to changes in diet, climate and disease.

*Full Text Word Count:* 4657*ISSN: *0036-8733 *Accession Number:
*32562823Section:
HUMAN ORIGINS Traces of a DISTANT PAST

DNA furnishes an ever clearer picture of the multimillennial trek from
Africa all the way to the tip of South America

A development company controlled by Osama bin Laden's half brother revealed
last year that it wants to build a bridge that will span the Bab el Mandeb,
the outlet of the Red Sea to the Indian Ocean. If this ambitious project is
ever realized, the throngs of African pilgrims who traverse one of the
longest bridges in the world on a journey to Mecca would pass hundreds of
feet above the probable route of the most memorable journey in human
history. Fifty or sixty thousand years ago a small band of Africans--a few
hundred or even several thousand--crossed the strait in tiny boats, never to
return.

The reason they left their homeland in eastern Africa is not completely
understood. Perhaps the climate changed, or once abundant shellfish stocks
vanished. But some things are fairly certain. Those first trekkers out of
Africa brought with them the physical and behavioral traits-- the large
brains and the capacity for language-- that characterize fully modern
humans. From their bivouac on the Asian continent in what is now Yemen, they
set out on a decamillennial journey that spanned continents and land bridges
and reached all the way to Tierra del Fuego, at the bottom of South America.

Scientists, of course, have gained insight into these wanderings because of
the fossilized bones or spearheads laboriously uncovered and stored in
collections. But ancestral hand-me-downs are often too scant to provide a
complete picture of this remote history. In the past 20 years population
geneticists have begun to fill in gaps in the paleoanthropological record by
fashioning a genetic bread-crumb trail of the earliest migrations by modern
humans.

Almost all our DNA--99.9 percent of the three billion "letters," or
nucleotides, that make up the human genome--is the same from person to
person. But interwoven in that last 0.1 percent are telltale differences. A
comparison among, say, East Africans and Native Americans can yield vital
clues to human ancestry and to the inexorable progression of colonizations
from continent to continent. Until recent years, DNA passed down only from
fathers to sons or from mothers to their children has served as the
equivalent of fossilized footprints for geneticists. The newest research
lets scientists adjust their focus, widening the field of view beyond a few
isolated stretches of DNA to inspect hundreds of thousands of nucleotides
scattered throughout the whole genome.
[Continued . . . ]



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