[language] [Fwd: [evol-psych] Humans emerged 'out of Africa' again and again]

[H.M. Hubey]

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-------- Original Message --------
     Subject: [evol-psych] Humans emerged 'out of Africa' again and
              again
        Date: Thu, 07 Mar 2002 07:09:35 +0000
        From: Ian Pitchford <ian.pitchford at scientist.com>
    Reply-To: Ian Pitchford <ian.pitchford at scientist.com>
Organization: http://human-nature.com/
          To: evolutionary-psychology at yahoogroups.com

Public release date: 6-Mar-2002
Contact: Tony Fitzpatrick
tony_fitzpatrick at aismail.wustl.edu
314-935-5272
Washington University in St. Louis

Humans emerged 'out of Africa' again and again

St. Louis, March 6, 2002, 1 p.m. CST - Analyses of recently derived
human
genetic trees by Alan R. Templeton, Ph.D, of Washington University in St
Louis,
show that there were at least two major waves of human migration out of
Africa.
DNA evidence suggests also that these wanderers bred with the people
they
encountered, rather than replaced them, in a "make-
love-not-war,"scenario.
Templeton, Charles Rebstock Professor of Biology in Arts & Sciences at
Washington University, combined evidence from many different populations
and
many different genes in an analysis to reconstruct their movement and
history.

Africa has played a dominant role in shaping the modern gene pool
through
successive population expansions, he says in the March 7, 2002 issue of
Nature.
But these populations interbreeding with resident populations means that

genetic interchange between populations has occurred everywhere
throughout
history.

Templeton analyzed human genetic trees for maternally inherited
mitochondrial
DNA, paternally inherited Y-chromosomal DNA, and eight other DNA regions
,
including two on the X chromosome, to reach his conclusions. He used a
computer
program called GEODIS, which he created in 1995 and later modified with
the
help of David Posada, Ph.D., and Keith Crandall, Ph.D. at Brigham Young
University, to determine genetic relationships among and within
populations
based on an examination of specific haplotypes, clusters of genes that
are
inherited as a unit. Templeton's study is based on 10 DNA regions, while
most
other genetic analyses focus on just one, mitochondrial DNA, for
instance. It
also differs from most approaches because it uses a statistical approach
with a
priori inference criteria but requires no prior model of human
evolution. Most
others have a model in mind, and then see if the data are compatible
with it.

GEODIS analyses place an older expansion out of Africa between 420,000
and
840,000 years ago and a more recent one between 80,000 and 150,000 years
ago.
GEODIS analyses also show conclusively, Templeton states, that the most
recent
out-of-Africa expansion event was not a replacement event. Replacement
means
the new population wiped out an existing one in Europe or Asia,
resulting in
their complete genetic extinction.

"If it had been (a replacement event), the three significant genetic
signatures
of the older expansion event and the six significant genetic signatures
of
older recurrent gene flow would have been wiped away," Templeton writes.

It is likely that the earlier out-of-Africa expansion also was
characterized by
interbreeding rather than replacement, but Templeton emphasizes that the

evidence for this is tentative because the probability of such old gene
flow is
not statistically high enough.

"Humans expanded again and again out of Africa," Templeton concludes,
"but
these expansions resulted in interbreeding, not replacement, and thereby

strengthened the genetic ties between human populations throughout the
world."

The work was supported in part by a Burroughs Wellcome Fund Innovation
Award in
Functional Genomics.

Templeton, who joined the Washington University faculty in 1977, is a
renowned
population and evolutionary biologist who has analyzed the genomes of
many
different species to better understand their evolution and their
survival.
Since 1984, he has been the head of the Evolutionary and Population
Biology
Program in Washington University's Division of Biological Sciences.

Templeton's contributions to the controversy of recent human evolution
include
dashing the popular 'Eve Theory' because of flaws he detected in
researchers'
1987 computer analyses. In 1998, he published a paper in American
Anthropologist that explained humans as one race, instead of a species
with
subdivisions, or races. His study showed that, among people now
categorized by
race, everyone shares about 85 percent of the same genes. The 15 percent
of
variation is not enough difference to separate people biologically.

http://www.eurekalert.org/pub_releases/2002-03/wuis-he030402.php

______

Nature 416, 45 - 51 (2002)

Out of Africa again and again

ALAN TEMPLETON

Department of Biology, Washington University, St Louis, Missouri
63130-4899,
USA
Correspondence and requests for materials should be addressed to A.R.T.
(e-mail: temple_a at biology.wustl.edu).

The publication of a haplotype tree of human mitochondrial DNA variation
in
1987 provoked a controversy about the details of recent human evolution
that
continues to this day. Now many haplotype trees are available, and new
analytical techniques exist for testing hypotheses about recent
evolutionary
history using haplotype trees. Here I present formal statistical
analysis of
human haplotype trees for mitochondrial DNA, Y-chromosomal DNA, two
X-linked
regions and six autosomal regions. A coherent picture of recent human
evolution
emerges with two major themes. First is the dominant role that Africa
has
played in shaping the modern human gene pool through at least two-not
one-major
expansions after the original range extension of Homo erectus out of
Africa.
Second is the ubiquity of genetic interchange between human populations,
both
in terms of recurrent gene flow constrained by geographical distance and
of
major population expansion events resulting in interbreeding, not
replacement.

http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v416/n6876/abs/416045a_fs.html

__________

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