Marc Verha
Wed, Jul-18-07, 17:16
Modern Humans Came Out of Africa, "Definitive" Study Says
James Owen for National Geographic News July 18, 2007
We are solely children of Africa-with no Neandertals or
island-dwelling "hobbits" in our family tree, according to a
new study.
Scientists who compared the skulls and DNA of human remains
from around the world say their results point to modern humans
(Homo sapiens) having a single origin in Africa.
The study didn't find any evidence to suggest that human
species living elsewhere in the world contributed to our
direct ancestors' make-up.
A team led by Andrea Manica at the University of Cambridge,
England, combined analysis of global genetic variations with
comparisons of more than 6,000 skulls from more than a hundred
ancient human populations.
The team found that loss of genetic diversity was very closely
mirrored by reduced physical variation the farther away people
lived from Africa. (Explore our human roots.)
Only Out of Africa
The new data support the single origin, or "out of Africa"
theory for anatomically modern humans, which says that these
early humans colonized the planet after spreading out of the
continent some 50,000 years ago.
In the past, experts have also argued a "multiregional"
theory, which held that Homo sapiens arose from different
human populations in different areas of the world.
"The origin of anatomically modern humans has been the focus
of much-heated debate," lead author Manica said.
"We have combined our genetic data with new measurements of a
large sample of skulls to show definitively that modern humans
originated from a single area."
Previous studies have found that genetic differences in human
populations can be explained by distance from Africa.
The new study also looked at 37 measurements from male and
female skulls from around the world. The chosen skulls
were all less than 2,000 years old, making them better
preserved and more likely to give accurate measurements
than older skulls.
Many skull features were determined by the different
environments where the species had lived.
But distance from Africa was still found to account for up to
25 percent of variation in the features.
'Remarkable' Similarity
The researchers made sure that the DNA analysis used the same
framework as the analysis for the skulls-so the two could be
fully compared, Manica said.
"I would argue we had two independent shots at getting the
same answer, and remarkably, the answer is exactly the
same," he added.
The lowest amount of variation was found in ancient
populations from South America and Australia, the two main
inhabited regions most remote from Africa.
The study team, writing in the latest issue of the journal
Nature, argues that this low variation in remote regions would
be expected if Homo sapiens arose solely in Africa.
That's because populations built up genetic and physical
diversity for some 150,000 years before the fossil record
suggests the first pioneers started spreading elsewhere.
But it wasn't until between about 20,000 and 30,000 years ago
that modern humans reached South America and Australia, the
team noted.
"The more you move away from that center of diversity where
you started, the less diversity you have," Manica said.
This pattern was remarkably consistent globally, the
researchers found.
The study places the original roots of modern humans in
south-central Africa. In the middle of this region lies the
Great Rift Valley-often referred to as the "cradle of
humanity." (See a map of Africa.)
Some researchers believe that modern humans are at least
in part the product of non-African species descended from
Homo habilis, which left Africa at least 1.5 million years
ago. (Related: "China's Earliest Modern Human Found"
[April 3, 2007].)
Such groups include the Neandertals of Europe and western
Asia, archaic human types in eastern Asia and Australia, and
perhaps even the controversial hobbit humans from the
Indonesian island of Flores. (Related: "Hobbit-Like Human
Ancestor Found in Asia" [October 27, 2004].)
'No Other Source'
"What we can confidently say is that there has not been a wave
[of anatomically modern humans] starting from somewhere else,
because then you'd find a second area with more variability,"
Manica said.
What Manica can't say is "that matings with the Neandertals
never ever happened, but if it did happen, none of the
descendants stayed around." Effectively, any mating had no
contribution whatsoever to modern humans, he added.
Anthropologist Erik Trinkhaus of Washington University in St.
Louis, Missouri, has found fossil evidence suggesting that
Homo sapiens and Neandertals did interbreed. Trinkhaus is
critical of the latest findings. (Related: "Neandertals,
Modern Humans May Have Interbred, Skull Study Suggests"
[January 16, 2007].)
Certain genetic and anatomical traits "cannot be explained as
a simple and complete expansion of modern humans out of
Africa," he said.
"The idea that humans get more uniform further from Africa is
simply ludicrous," he added, noting that modern-day Chinese
and Australian Aborigines look no more similar to each other
than do Africans and Europeans.
Fred Smith, an anthropologist at Loyola University of Chicago
who is unaffiliated with the research, agrees that the
findings confirm there is an African origin for modern humans.
Smith nevertheless argues that the study is not at odds with
the idea he first proposed in 1989 that there was "some
low-level assimilation of archaic peoples into these modern
populations."
And Charles Roseman, of the University of Illinois at
Urbana-Champaign, said: "It could very well be that there was
a recent out-of-Africa expansion, coupled with some either
small or large amount of genetic exchange with humans outside
of Africa." http://news.nationalgeographic.com/news/2007/07/0-
70718-african-origin.html
James Owen for National Geographic News July 18, 2007
We are solely children of Africa-with no Neandertals or
island-dwelling "hobbits" in our family tree, according to a
new study.
Scientists who compared the skulls and DNA of human remains
from around the world say their results point to modern humans
(Homo sapiens) having a single origin in Africa.
The study didn't find any evidence to suggest that human
species living elsewhere in the world contributed to our
direct ancestors' make-up.
A team led by Andrea Manica at the University of Cambridge,
England, combined analysis of global genetic variations with
comparisons of more than 6,000 skulls from more than a hundred
ancient human populations.
The team found that loss of genetic diversity was very closely
mirrored by reduced physical variation the farther away people
lived from Africa. (Explore our human roots.)
Only Out of Africa
The new data support the single origin, or "out of Africa"
theory for anatomically modern humans, which says that these
early humans colonized the planet after spreading out of the
continent some 50,000 years ago.
In the past, experts have also argued a "multiregional"
theory, which held that Homo sapiens arose from different
human populations in different areas of the world.
"The origin of anatomically modern humans has been the focus
of much-heated debate," lead author Manica said.
"We have combined our genetic data with new measurements of a
large sample of skulls to show definitively that modern humans
originated from a single area."
Previous studies have found that genetic differences in human
populations can be explained by distance from Africa.
The new study also looked at 37 measurements from male and
female skulls from around the world. The chosen skulls
were all less than 2,000 years old, making them better
preserved and more likely to give accurate measurements
than older skulls.
Many skull features were determined by the different
environments where the species had lived.
But distance from Africa was still found to account for up to
25 percent of variation in the features.
'Remarkable' Similarity
The researchers made sure that the DNA analysis used the same
framework as the analysis for the skulls-so the two could be
fully compared, Manica said.
"I would argue we had two independent shots at getting the
same answer, and remarkably, the answer is exactly the
same," he added.
The lowest amount of variation was found in ancient
populations from South America and Australia, the two main
inhabited regions most remote from Africa.
The study team, writing in the latest issue of the journal
Nature, argues that this low variation in remote regions would
be expected if Homo sapiens arose solely in Africa.
That's because populations built up genetic and physical
diversity for some 150,000 years before the fossil record
suggests the first pioneers started spreading elsewhere.
But it wasn't until between about 20,000 and 30,000 years ago
that modern humans reached South America and Australia, the
team noted.
"The more you move away from that center of diversity where
you started, the less diversity you have," Manica said.
This pattern was remarkably consistent globally, the
researchers found.
The study places the original roots of modern humans in
south-central Africa. In the middle of this region lies the
Great Rift Valley-often referred to as the "cradle of
humanity." (See a map of Africa.)
Some researchers believe that modern humans are at least
in part the product of non-African species descended from
Homo habilis, which left Africa at least 1.5 million years
ago. (Related: "China's Earliest Modern Human Found"
[April 3, 2007].)
Such groups include the Neandertals of Europe and western
Asia, archaic human types in eastern Asia and Australia, and
perhaps even the controversial hobbit humans from the
Indonesian island of Flores. (Related: "Hobbit-Like Human
Ancestor Found in Asia" [October 27, 2004].)
'No Other Source'
"What we can confidently say is that there has not been a wave
[of anatomically modern humans] starting from somewhere else,
because then you'd find a second area with more variability,"
Manica said.
What Manica can't say is "that matings with the Neandertals
never ever happened, but if it did happen, none of the
descendants stayed around." Effectively, any mating had no
contribution whatsoever to modern humans, he added.
Anthropologist Erik Trinkhaus of Washington University in St.
Louis, Missouri, has found fossil evidence suggesting that
Homo sapiens and Neandertals did interbreed. Trinkhaus is
critical of the latest findings. (Related: "Neandertals,
Modern Humans May Have Interbred, Skull Study Suggests"
[January 16, 2007].)
Certain genetic and anatomical traits "cannot be explained as
a simple and complete expansion of modern humans out of
Africa," he said.
"The idea that humans get more uniform further from Africa is
simply ludicrous," he added, noting that modern-day Chinese
and Australian Aborigines look no more similar to each other
than do Africans and Europeans.
Fred Smith, an anthropologist at Loyola University of Chicago
who is unaffiliated with the research, agrees that the
findings confirm there is an African origin for modern humans.
Smith nevertheless argues that the study is not at odds with
the idea he first proposed in 1989 that there was "some
low-level assimilation of archaic peoples into these modern
populations."
And Charles Roseman, of the University of Illinois at
Urbana-Champaign, said: "It could very well be that there was
a recent out-of-Africa expansion, coupled with some either
small or large amount of genetic exchange with humans outside
of Africa." http://news.nationalgeographic.com/news/2007/07/0-
70718-african-origin.html