Language and Genetics

Hi Folks

Have a look at the attached, posted to the Darwin list. Thought some
might be interested on how genetics is showing human migrations that
may (or may not) show up in language.

One way is that Geneticists can track emigrations because of the
train of errors that slowly accumulates in certain regions of the
DNA. After a population splits, the people who go east will clock up
a different set of errors from those who venture west.

From the population splits implied by these error patterns,
geneticists can reconstruct family trees of different lineages in the
grand genealogy of humankind, and even assign rough dates to the
branch points. At this year's conference, which ended last week, Dr.
Peter Underhill of Stanford showed how scholars could begin to link
the data in the genome's archive with historical events. Anatolia,
the ancient name for Turkey, has long been a corridor for armies and
peoples traveling between Europe and Asia.

Dr. Underhill, who has reconstructed the worldwide tree of the Y
chromosome, has been analyzing the various Y chromosome lineages
present in today's Turkish population. He has found one lineage whose
ancestors may have carried the agricultural revolution from Anatolia
to Europe during the Neolithic era, 8,000 to 3,000 years ago.
Anatolians with another lineage may be descendants of the Bronze Age
Hattic culture, he said.

Curiously the Seljuk Turks, who wrested Anatolia from the Byzantine
Empire in the 11th century, have left only a faint genetic signal of
their presence, Dr. Underhill said. Though the conquerors imposed
their language and culture over a wide region, an army of a mere
40,000 made little genetic difference to a population that had
already reached 12 million by Roman times.

Just as the Y chromosome tracks the movement of men, an element
called mitochondrial DNA, inherited only through the egg, traces the
journeys of women. Dr. Douglas Wallace of the University of
California at Irvine long ago defined and named the principal
mitochondrial lineages. Only three of the 20 or so lineages,
designated A, C and D, are found in northern Siberia. Given that
northern Asia is essentially a big plain with no obstacle but
freezing cold, Dr. Wallace wondered why none of the other lineages
had made it to the far northeast.

He now believes, he said at the meeting, that the three mitochondrial
lineages carry an altered form of an energy metabolism gene that may
improve the body's resistance to cold. This could explain why A, C
and D are the principal lineages found in Native Americans: their
ancestors, being better adapted to life in northern Siberia, would
have discovered the Beringian land bridge to Alaska before it was
submerged at the end of the last ice age.

Most of the available evidence suggests there was only one emigration
of modern humans from Africa, a small group that left some 40,000 to
50,000 years ago and populated first Asia and then Europe. But some
geneticists think there may have been an earlier exodus of people who
traveled by boat along the southern Asian coasts, eventually reaching
Australia. The people of Australia and Papua New Guinea are dark
skinned and somewhat different from most other Asians and Europeans.
To test the idea of a southern route, Dr. James F. Wilson of
University College London compared the DNA of the Dravidian-speaking,
dark skinned aboriginal tribes of southern India with that of New
Guinea highlanders to see if the two might be part of the same
exodus. The first gene he looked at suggested they were related, but
further study showed otherwise.

"The distinctiveness of New Guineans could be from long-term drift,
not a different route out of Africa," he said. Drift is the
geneticist's term for the random change that takes place between
generations as some genetic variants become more common and others
get rarer or disappear altogether.

Dr. David Reich of the Whitehead Institute in Cambridge, Mass.,
described an ingenious method to recognize recently selected genes,
based on the length of the unchanged DNA that the beneficial mutation
drags along with it between generations.

A different method was described by Dr. Mark Stoneking of the Max
Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
He figured that genes that differ widely among ethnic groups have
probably been under selective pressure because of different diets,
parasites, diseases or climates confronted by their owners.

With this approach Dr. Stoneking has found a gene that has three
major variants: one dominates in Europeans, one in Africans and one
in Asians. The gene, known as F13B, codes for part of Factor XIII in
the cascade of blood-clotting proteins. It is not known why it should
have different common forms in the three major population groups.
A broader approach, made possible by a large-scale DNA sequencing
program, was discussed by Dr. Benjamin Salisbury of Genaissance
Pharmaceuticals in New Haven. He too looked for genes whose variant
forms have very different frequencies among races by decoding some
4,000 genes in 82 people.

Dr. Salisbury said he had found many such genes, including one that
is absent from Africans and Europeans but found in 88 percent of
Asians. He declined for commercial reasons to identify the gene.
Genes under intense selective pressure are of great interest because
those selected for disease resistance may pinpoint new targets for
drug development. Other selected genes may define what it means to be
human.

Linguists and geneticists last year discovered a human gene called
FOXP2 which differs in two essential places from the equivalent gene
in chimpanzees. The gene seems to underlie the articulation of
rapidly spoken language. It must be of great importance because a
single version is found in all humans. It came to light because
several members of a large London family with a damaged version of
the gene have severe difficulties with spoken language.

The discovery of this language gene, which seems to have arisen
sometime within the last 100,000 years, lends support to a bold idea
advanced by Dr. Richard Klein, an archaeologist at Stanford. He has
noted the sudden appearance in the archaeological record about 50,000
years ago of many sophisticated activities, like art, long distance
trade and intricate implements.

Anatomically modern humans first emerged some 130,000 years ago,
and those of 50,000 years ago appear no different. So Dr. Klein
believes some neural and cognitive change, most probably the
development of language, occurred in Africa around this time, before
the exodus to the rest of the world.

Dr. Klein describes himself as being in "a minority of one" among
experts on the period but notes that archaeologists tend to favor
culture, not genes, to explain their findings. At last week's meeting
his opponents argued that many modern behaviors appeared well before
50,000 years ago.

"One does not need to resort to a genetic black box; it's more likely
that we are seeing a response to climate change," said Dr. Alison
Brooks of George Washington University.

Dr. Sally McBrearty of the University of Connecticut described a
70,000-year-old crosshatched object recently found in the Blombos
cave on the coast of South Africa as "the smoking gun" evidence that
the people of that time were capable of symbolic representation.

Dr. Klein, who could not make a scheduled appearance at the
conference, said in a telephone interview that the new finds had not
changed his views. Similar artifacts, like mineral pigments, are
known from pre-50,000-year sites in Europe, he said. But the makers
of the artifacts were Neanderthals, who are not generally thought of
as modern.

Before 50,000 years ago the evidence for modern behavior is rare and
the dates are disputable, Dr. Klein said. After 50,000 years ago,
neither is the case.

The FOXP2 gene cannot be dated precisely because it is universal. But
other language genes yet to be found might be more helpful in
deciding when language was acquired. "This is the only test of my
theory, in the genome," Dr. Klein said.