Mohan:
Mohan:
Consider this: Modern European's ancestor is an Asian.
Out of Africa to India and not Europe
Neanderthals in Europe Stemmed early penetration of Humans out of Africa.
We started talking only 50Ky yrs ago
The Neanderthals who may have blocked the human advance out of Africa 100,000 years ago were now rapidly displaced in
Europe, presumably by behaviorally modern people invading Europe from Asia.
nytimes.com
Genes Tell New Story on the Spread of Man
Out of Africa
By NICHOLAS WADE
wo genetic surveys of human populations bring new evidence to bear on a pivotal event in prehistory, the first dispersal of modern humans from Africa.
One study, based on analysis of people in East Africa and India, suggests that the first emigration of modern humans was eastward, toward Asia, and not northward through the eastern Mediterranean.
A second, drawing on DNA data from 50 ethnic groups around the world, concludes
that the ancestral population from which the first emigrants came may have numbered as few as 2,000 people.
Both studies suggest that the most recent common ancestor of the emigrants lived
60,000 to 40,000 years ago.
Previous genetic studies have suggested 100,000 years or so for the most recent common ancestor, and about 10,000 for the ancestral population size.
The younger date of about 50,000 years seems to tally much better with an emerging synthesis of the archaeological data relating to human origins.
"A combination of fossil and genetic evidence locates the ancestral population in Africa, and archaeological discoveries imply an initial
dispersal out of Africa about 50 ky years ago," Dr. Richard G. Klein of
Stanford University writes in the latest edition of his book "The Human
Career." The term 50 ky means 50,000 years ago.
Dr. Klein believes an important distinction can be discerned in the
archaeological record between what he calls anatomically modern humans
and behaviorally modern humans. Though the fossil remains of each type
look the same, a more advanced set of stone tools appears with human
remains dating back to 50,000 years or so.
Modern human sites older than this have a more primitive set of stone
implements, similar to those used by archaic humans like the Neanderthals.
Dr. Klein and others believe that some major genetically based
neurological change, like the development of language, occurred about
50,000 years ago. This transformation, he infers, was the spur that led
behaviorally modern humans to innovate their characteristic suite of more
advanced stone implements, develop the first forms of art and spread
throughout the world.
Remains of modern humans dating to about 100,000 years ago have been
found at a well-known archaeological site called Skhul in Israel. The
finding has been interpreted as evidence of the first human migration out of
Africa, and it fit with the old genetic data of a modern human origin.
But the Neanderthals occupied Europe and the eastern coast of the
Mediterranean at that time, and they or the cold climate might have
blocked any further advance in that direction.
Dr. Klein's data suggest that the humans of 100,000 years ago,
anatomically modern but not like modern people in their behavior, did not
spread out of Africa at that time.
A new genetic study, by Dr. A. Silvana Santachiara-Benerecetti of the
University of Pavia in Italy and colleagues, confirms the view that the first
dispersal of modern humans was not until about 50,000 years ago, and that
the direction was eastward toward Asia.
The study, published in Nature Genetics last week, is based on
mitochondrial DNA, the genetic material of the small energy-producing
organelles inside every cell. Because mitochondria are inherited with the
egg, from the mother alone, their DNA escapes the shuffling that occurs in
sexual reproduction, and any changes reflect the occasional random
mutation in the DNA.
On the basis of these mutations, biologists can construct a family tree of
mitochondrial lineages and, by estimating the mutation rate, figure out the
time that has elapsed since the mutation at the root of the tree.
Dr. Santachiara-Benerecetti and her colleagues studied a particular pattern
of mitochondrial DNA that is well known in India. They found an earlier
form of the pattern among people in Ethiopia, suggesting that East Africa
was its place of origin.
Signs of the pattern also exist among many people in Saudi Arabia, but not
among inhabitants of the eastern Mediterranean.
This provides the first genetic evidence, the Italian biologists say, that the
human migration route out of Africa was from eastern Africa along the
coast toward Southeast Asia and Australia.
Another new genetic study, by Dr. Marcus Feldman of Stanford University
and others, makes an interesting counterpart to the Italian study because it
is based on a different kind of DNA but reaches similar conclusions.
Dr. Feldman and his colleagues looked at segments of the Y chromosome,
another part of the human genome that escapes the usual shuffling of the
reproductive process. Studying Y chromosomes from around the world,
they concluded that the most recent common ancestor of all these Y's was
carried by a man who lived only 40,000 years or so ago.
Even though all Y chromosomes can be traced back to a single individual,
this does not mean a single Adam was the species' only male
representative. The founding population from which the world's present
population is derived consisted of about 2,000 individuals, according to the
new data, Dr. Feldman said.
One Y chromosome in such a population will eventually dominate in the
descendants after all the other Y lineages are brought to a halt, whether
because their owners have no children or beget only daughters.
The 40,000-year date, which has a large range of uncertainty, is much
more recent than others, in part because the earlier estimates were forced
to assume, quite unrealistically, that the size of the human population
remained constant throughout prehistory. Dr. Feldman assumed an
exponentially expanding population, which yields a more recent date of
origin. His study is published in the current issue of the journal Molecular
Biology and Evolution.
The two new studies represent a convergence of the genetic and
archaeological data bearing on modern human origins, said Dr. Luca
Cavalli-Sforza, a leading population geneticist at Stanford University, who
was not an author of either study. The two independent lines of evidence
support the idea that behaviorally modern humans arose in Africa around
50,000 years ago from their anatomically modern forebears.
These behaviorally modern humans "had three big improvements in culture
-- language, boats or rafts, and Aurignacian technology," Dr. Cavalli-Sforza
said, referring to the more sophisticated stone implements.
Shortly after they had acquired these innovations, they burst forth to inhabit
the rest of the globe. The Neanderthals who may have blocked the human
advance out of Africa 100,000 years ago were now rapidly displaced in
Europe, presumably by behaviorally modern people invading Europe from
Asia. There are convincing dates, Dr. Cavalli-Sforza said, that humans
reached Europe by 40,000 years ago and Oceania and New Guinea by
40,000 to 50,000 years ago.
Although no boats from this period have yet been recovered, such craft
would have been essential transport for the early people who reached
Australia, and Dr. Cavalli-Sforza said he was convinced that "the people
who went from Africa to Asia knew how to use some simple navigational
means." |
