Early Humans Settled India Before Europe, Study Suggests
Early Humans Settled India Before Europe, Study Suggests
Brian Vastag
for National Geographic News
November 14, 2005
Modern humans migrated out of Africa and into India much earlier than once believed, driving older hominids in present-day India to extinction and creating some of the earliest art and architecture, a new study suggests.
The research places modern humans in India tens of thousands of years before their arrival in Europe.
University of Cambridge researchers Michael Petraglia and Hannah James developed the new theory after analyzing decades' worth of existing fieldwork in India. They outline their research in the journal Current Anthropology.
"He's putting all the pieces together, which no one has done before," Sheela Athreya, an anthropologist at Texas A&M University, said of Petraglia.
Modern humans arrived in Europe around 40,000 years ago, leaving behind cave paintings, jewelry, and evidence that they drove the Neandertals to extinction.
Petraglia and James argue that similar events took place in India when modern humans arrived there about 70,000 years ago.
The Indian subcontinent was once home to Homo heidelbergensis, a hominid species that left Africa about 800,000 years ago, Petraglia explained.
"I realized that, my god, modern humans might have wiped out Homo heidelbergensis in India," he said. "Modern humans may have been responsible for wiping out all sorts of ancestors around the world."
"Our model of India is talking about that entire wave of dispersal," he added. "[T]hat's a huge implication for paleoanthropology and human evolution."
A New Model
Petraglia and James reached their conclusions by pulling together fossils, artifacts, and genetic data.
The evidence points to an early human migration through the Middle East and into India, arriving in Australia by 45,000 to 60,000 years ago, they say.
Their model begins about 250,000 years ago, when Homo heidelbergensis arrived in India toting crude stone tools. Digs in central India in the 1980s turned up skeletal remains of the species, and other sites revealed almond-shaped hand axes chipped from stone.
Meanwhile in Africa modern humans arose about 190,000 years ago, most archaeologists believe. These humans too developed stone tools.
Scattered evidence, such as red ochre—perhaps used as body paint—suggests early African humans also dabbled in the creative arts.
The new theory posits that as much as 70,000 years ago, a group of these modern humans migrated east, arriving in India with technology comparable to that developed by Homo heidelbergensis.
"The tools were not so different," Petraglia says. "The technology that the moderns had wasn't of a great advantage over what [Homo heidelbergensis] were using."
But modern humans outcompeted the natives, slowly but inexorably driving them to extinction, Petraglia says. "It's just like the story in Western Europe, where [modern humans] drove Neandertals to extinction," he says.
The modern humans who colonized India may also have been responsible for the disappearance of the so-called Hobbits, whose fossilized bones were discovered recently on the Indonesian island of Flores.
But Athreya of Texas A&M argues that the evidence for such a "replacement event" in India remains weak.
"You have to explain the reasons for the replacement, [such as] technical superiority," she said.
"The genetic evidence shows there were multiple migrations out of Africa, so there would have been multiple migrations into [India]. But I think these migrating populations didn't completely replace the indigenous group."
Early Art
Petraglia and James's report presents evidence of creativity and culture in India starting about 45,000 years ago. Sophisticated stone blades arrive first, along with rudimentary stone architecture.
Beads, red ochre paint, ostrich shell jewelry, and perhaps even shrines to long-lost gods—the hallmarks of an early symbolic culture—appear by 28,500 years ago.
This slow change is in contrast to what many scientists believe played out in Europe. Modern humans blew through the continent like a storm about 40,000 years ago, and Neandertals quickly disappeared.
The switch happened so rapidly—as evidenced by the sudden arrival of advanced stone tools and an explosion of cave painting and other art—that anthropologists call it the "human revolution."
"What we have is a much patchier, very slow and gradual accumulation of what we call modern human behavior in South Asia," Petraglia says.
"And that just simply means that culture developed in a slightly different way in South Asia than it did in Western Europe."
A dearth of fossils and artifacts in India makes Petraglia and James's research even more valuable, writes Robin Dennell, professor of archeology at the University of Sheffield, in a comment accompanying the study.
The subcontinent has produced just one set of early Homo sapiens fossils, found in a cave in Sri Lanka and dated to about 36,000 years ago.
Despite this, Petraglia hopes his analysis throws new light onto early human history in India.
"We're trying to give a wake up call to anthropologists … saying that we have to be looking at all parts of the world," he says.
"If we really want to tell the story of human evolution we've got to bring all parts of the world into the story." _________________ La vie est un privilege, elle ne vous doit rien!
Vous lui devez tout, en l'occurence votre vie
Scientists Find A DNA Change That Accounts For White Skin
By Rick Weiss
Washington Post Staff Writer
Friday, December 16, 2005; Page A01
Scientists said yesterday that they have discovered a tiny genetic mutation that largely explains the first appearance of white skin in humans tens of thousands of years ago, a finding that helps solve one of biology's most enduring mysteries and illuminates one of humanity's greatest sources of strife.
The work suggests that the skin-whitening mutation occurred by chance in a single individual after the first human exodus from Africa, when all people were brown-skinned. That person's offspring apparently thrived as humans moved northward into what is now Europe, helping to give rise to the lightest of the world's races.
Leaders of the study, at Penn State University, warned against interpreting the finding as a discovery of "the race gene." Race is a vaguely defined biological, social and political concept, they noted, and skin color is only part of what race is -- and is not.
In fact, several scientists said, the new work shows just how small a biological difference is reflected by skin color. The newly found mutation involves a change of just one letter of DNA code out of the 3.1 billion letters in the human genome -- the complete instructions for making a human being.
"It's a major finding in a very sensitive area," said Stephen Oppenheimer, an expert in anthropological genetics at Oxford University, who was not involved in the work. "Almost all the differences used to differentiate populations from around the world really are skin deep."
The work raises a raft of new questions -- not least of which is why white skin caught on so thoroughly in northern climes once it arose. Some scientists suggest that lighter skin offered a strong survival advantage for people who migrated out of Africa by boosting their levels of bone-strengthening vitamin D; others have posited that its novelty and showiness simply made it more attractive to those seeking mates.
The work also reveals for the first time that Asians owe their relatively light skin to different mutations. That means that light skin arose independently at least twice in human evolution, in each case affecting populations with the facial and other traits that today are commonly regarded as the hallmarks of Caucasian and Asian races.
Several sociologists and others said they feared that such revelations might wrongly overshadow the prevailing finding of genetics over the past 10 years: that the number of DNA differences between races is tiny compared with the range of genetic diversity found within any single racial group.
Even study leader Keith Cheng said he was at first uncomfortable talking about the new work, fearing that the finding of such a clear genetic difference between people of African and European ancestries might reawaken discredited assertions of other purported inborn differences between races -- the most long-standing and inflammatory of those being intelligence.
"I think human beings are extremely insecure and look to visual cues of sameness to feel better, and people will do bad things to people who look different," Cheng said.
The discovery, described in today's issue of the journal Science, was an unexpected outgrowth of studies Cheng and his colleagues were conducting on inch-long zebra fish, which are popular research tools for geneticists and developmental biologists. Having identified a gene that, when mutated, interferes with its ability to make its characteristic black stripes, the team scanned human DNA databases to see if a similar gene resides in people.
To their surprise, they found virtually identical pigment-building genes in humans, chickens, dogs, cows and many others species, an indication of its biological value.
They got a bigger surprise when they looked in a new database comparing the genomes of four of the world's major racial groups. That showed that whites with northern and western European ancestry have a mutated version of the gene.
Skin color is a reflection of the amount and distribution of the pigment melanin, which in humans protects against damaging ultraviolet rays but in other species is also used for camouflage or other purposes. The mutation that deprives zebra fish of their stripes blocks the creation of a protein whose job is to move charged atoms across cell membranes, an obscure process that is crucial to the accumulation of melanin inside cells.
Humans of European descent, Cheng's team found, bear a slightly different mutation that hobbles the same protein with similar effect. The defect does not affect melanin deposition in other parts of the body, including the hair and eyes, whose tints are under the control of other genes.
A few genes have previously been associated with human pigment disorders -- most notably those that, when mutated, lead to albinism, an extreme form of pigment loss. But the newly found glitch is the first found to play a role in the formation of "normal" white skin. The Penn State team calculates that the gene, known as slc24a5, is responsible for about one-third of the pigment loss that made black skin white. A few other as-yet-unidentified mutated genes apparently account for the rest.
Although precise dating is impossible, several scientists speculated on the basis of its spread and variation that the mutation arose between 20,000 and 50,000 years ago. That would be consistent with research showing that a wave of ancestral humans migrated northward and eastward out of Africa about 50,000 years ago.
Unlike most mutations, this one quickly overwhelmed its ancestral version, at least in Europe, suggesting it had a real benefit. Many scientists suspect that benefit has to do with vitamin D, made in the body with the help of sunlight and critical to proper bone development.
Sun intensity is great enough in equatorial regions that the vitamin can still be made in dark-skinned people despite the ultraviolet shielding effects of melanin. In the north, where sunlight is less intense and cold weather demands that more clothing be worn, melanin's ultraviolet shielding became a liability, the thinking goes.
Today that solar requirement is largely irrelevant because many foods are supplemented with vitamin D.
Some scientists said they suspect that white skin's rapid rise to genetic dominance may also be the product of "sexual selection," a phenomenon of evolutionary biology in which almost any new and showy trait in a healthy individual can become highly prized by those seeking mates, perhaps because it provides evidence of genetic innovativeness.
Cheng and co-worker Victor A. Canfield said their discovery could have practical spinoffs. A gene so crucial to the buildup of melanin in the skin might be a good target for new drugs against melanoma, for example, a cancer of melanin cells in which slc24a5 works overtime.
But they and others agreed that, for better or worse, the finding's most immediate impact may be an escalating debate about the meaning of race.
Recent revelations that all people are more than 99.9 percent genetically identical has proved that race has almost no biological validity. Yet geneticists' claims that race is a phony construct have not rung true to many nonscientists -- and understandably so, said Vivian Ota Wang of the National Human Genome Research Institute in Bethesda.
"You may tell people that race isn't real and doesn't matter, but they can't catch a cab," Ota Wang said. "So unless we take that into account it makes us sound crazy." _________________ La vie est un privilege, elle ne vous doit rien!
Vous lui devez tout, en l'occurence votre vie
L’ADN mitochondrial, le chromosome Y et l’histoire des populations humaines
Par:
Lluís Quintana-Murci
Reiner Veitia
Silvana Santachiara-Benerecetti
Ken McElreavey
Marc Fellous
Thomas Bourgeron
Citation:
De nombreuses disciplines étudient les origines de l’espèce
humaine. En particulier, l’archéologie, l’anthropologie, la linguistique
et la paléontologie tentent de retracer les grandes
étapes de notre passé.
Plus récemment, la génétique et la biologie
moléculaire ont permis de préciser l’origine des différentes
populations humaines en étudiant les variations génétiques
entre les individus.
Parmi tous les marqueurs génétiques utilisés, les plus intéressants sont les marqueurs
uniparentaux comme:
- l’ADN mitochondrial, hérité de la mère,
- et le chromosome Y, hérité du père
car ils échappent tous deux à la recombinaison méiotique.
Ainsi, contrairement aux autosomes ou au chromosome X,
- tous les ADN mitochondriaux présents dans les populations humaines peuvent provenir
d’un ancêtre maternel commun
- et les chromosomes Y, d’un ancêtre paternel commun.
Ces deux marqueurs ont donc été utilisés pour préciser géographiquement et historiquement
l’origine de nos ancêtres communs les plus récents et
les interactions entre les différentes populations humaines.
Citation:
Ainsi, l’homme de Java,l’homme de Pékin et l’homme de Neandertal n’auraient plus de descendants actuellement.
D’un point de vue génétique, l’ADN de ces individus et de ces populations
ne fait pas partie de l’ensemble des gènes actuels.
Citation:
On peut alors se poser la question :
comment la génétique peut-elle donner
des arguments en faveur de l’un
ou de l’autre modèle ?
Deux grandes stratégies ont été utilisées :
- l’étude de l’ADN des fossiles
- et l’étude de la diversité génétique des différentes
populations actuelles.
_________________ La vie est un privilege, elle ne vous doit rien!
Vous lui devez tout, en l'occurence votre vie
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