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<< News >> Study points to larger role of Asian ancestors in evolution

Submitted by coldrum on Thursday, 23 August 2007  Page Views: 2352

DiscoveriesA new analysis of the dental fossils of human ancestors suggests that Asian populations played a larger role than Africans in colonizing Europe millions of years ago, said a study released Monday.

The findings challenge the prevailing "Out of Africa" theory, which holds that anatomically modern man first arose from one point in Africa and fanned out to conquer the globe, and bolsters the notion that Homo sapiens evolved from different populations in different parts of the globe.

The "Out of Africa" scenario has been underpinned since 1987 by genetic studies based mainly on the rate of mutations in mitochondrial DNA, a cell material inherited from the maternal line of ancestry.

But for this study, European researchers opted to study the tooth fossil record of modern man's ancestors because of their high component of genetic expression.

The investigators examined the shapes of more than 5,000 teeth from human ancestors from Africa, Asia and Europe dating back millions of years.

They found that European teeth had more Asian features than African ones.

They also noted that the continuity of the Eurasian dental pattern from the Early Pleistocene until the appearance of Upper Pleistocene Neanderthals suggests that the evolutionary courses of the Eurasian and African continents were relatively independent for a long period.

"The history of human populations in Eurasia may not have been the result of a few high-impact replacement waves of dispersals from Africa, but a much more complex puzzle of dispersals and contacts among populations within and outside continents," the researchers wrote.

"In the light of these results, we propose that Asia has played an important role in the colonization of Europe, and that future studies on this issue are obliged to pay serious attention to the 'unknown' continent."

The paper was written by researchers at Spain's national center for research into human evolution in Burgos and appears in the journal of the Proceedings of the National Academy of Sciences.

news.yahoo.com.

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"Study points to larger role of Asian ancestors in evolution" | Login/Create an Account | 8 News and Comments
  
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Humans spread out of Africa later by coldrum on Thursday, 01 October 2009
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Humans spread out of Africa later

Modern humans spread out of Africa 20,000 years later than previously thought, according to new genetic research just published.
Scientists, including the Natural History Museum’s human origins expert Professor Chris Stringer, re-examined how scientists get dates for key events in human evolutionary history. They did this by finding new ways to analyse the data obtained from mitochondrial DNA (mtDNA).

Mitochondria are the tiny structures in each human cell that produce the cell’s power. They contain their own DNA and this is inherited through the mother.

‘We tried alternative ways to date recent episodes in human evolution, such as our split from Neanderthals, and we found these events occurred more recently in time,’ says Prof Stringer.

The new analysis revealed modern humans separated from Neanderthals around 300-400,000 years ago rather than previous estimates of 500-600,000 years.

The research suggested that modern humans migrated out of Africa between 55-60,000 years ago rather than the previous dates of 70-80,000 years.

They also got more recent dates for other crucial events such as the age of our African ancestral mother, known as mitochondrial Eve, from who all recent humans (Homo sapiens) descended. She was found to have lived around 110-130,000 years ago, rather than previous estimates of 150,000-200,000 years ago.

‘The new dates are consistent with the most recent fossil and archaeological data for Neanderthal evolution, our exit from Africa and our arrival in Asia, Australia, Europe and the Americas,’ says Prof Stringer.

‘And they also cast doubt on ideas of an early exit from Africa towards China and Australia.’

More information: Chris Stringer, Phillip Endicott, Simon Y.W. Ho, and Mait Metspalu's Evaluating the Mitochondrial Timescale of Human Evolution paper is published in the journal Trends in Ecology and Evolution.

Source: American Museum of Natural History (news : web)

http://www.physorg.com/news171286860.html

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Laetoli Ancient Footsteps to Get 'Facelift' by coldrum on Wednesday, 17 June 2009
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Laetoli Ancient Footsteps to Get 'Facelift'

The Ministry of Natural Resources and Tourism expects to spend Tsh.600 million on an excavation and preservation project of the famous ancient Laetoli footsteps in the Ngorongoro Conservation Area.

The Laetoli footsteps in Ngorongoro were discovered in 1979 on rocks and were expertly "sheltered" by researchers from Getty Foundation of the United States of America.

The Deputy Minister for Natural Resources and Tourism, Ezekiel Maige told news

reporters at Karatu that the government aimed at further promoting tourism in Ngorongoro by giving it another attraction through the project.

Maige said the project started following directives by President Jakaya Kikwete.
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He said initial preparations by experts from various departments were already underway and actual excavation and preservation process would start soon after.

Acting Chief Conservator for the Ngorongoro Conservation Area Authority (NCAA), Benard Murunya said the delay for the project implementation was due to the need for sophisticated expertise to avoid risk of damage due to windy weather at the locality.

Experts have planned to do the excavation work in phases and the sheltering be done using technology that would ensure preservation and allow people to view the steps at the same time, according to Murunya.

Archaeologists, tourism stakeholders, and members of public have been pressing to excavation and exposure of the ancient footsteps to attract more visitors from within and outside Tanzania.

http://allafrica.com/stories/200905181099.html
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New Analysis Suggests Earlier Start for Upright Walking by coldrum on Wednesday, 21 May 2008
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New Analysis Suggests Earlier Start for Upright Walking

As early as six million years ago, apparently close to the beginning of the human lineage, an ancestral species had already developed the transforming ability for upright walking, scientists reported on Thursday.

A new, more detailed analysis of a fossil thigh bone found eight years ago in Kenya yielded strong evidence that the species Orrorin tugensis stood and walked on its hind limbs. The scientists said this was the earliest known example of bipedal locomotion.

The findings are described in a report in the journal Science by Brian G. Richmond and William L. Jungers, paleoanthropologists at George Washington University and the State University of New York at Stony Brook, respectively. The research included an examination of the original fossils and a comparison with skeletons of modern humans and protohumans and also chimpanzees.

Although the French discoverers of the fossils, Martin Pickford and Brigitte Senut, had suspected that the species was bipedal, they said they were not sure, and other scientists were even more skeptical.

Dr. Richmond said in a telephone interview that he was given access to the bones, deposited in a bank vault in Nairobi, and made his independent tests under the watchful eyes of a guard. The size of the specimen’s hip joint, the shape and strength of the wide thigh bone, and other characteristics, he said, provided “convincing evidence to confirm Orrorin’s bipedal adaptations.”

The scientists said their analysis of hand and arm bones showed the species “most probably also climbed trees, presumably to forage, build nests and seek refuge.”

A more surprising result to emerge from the study appeared to contradict an earlier hypothesis about Orrorin’s relationship to later species in the human lineage, Dr. Richmond and Dr. Jungers said.

The fossils were first thought to be related more closely to the genus Homo than to Australopithecus, an intermediate genus that first emerged nearly four million years ago and included species living as recently as two million years ago. This seemed to make Orrorin a more direct human ancestor, possibly relegating “Lucy” and other australopithecines to a side branch of the family tree.

Dr. Richmond and Dr. Jungers found instead a close similarity between the Orrorin thigh bone and hip mechanics and those of Australopithecus. This suggests, they said, that the basic pattern of two-legged walking appeared very early in human evolution and persisted with only minor variations over a period of four million years.

“I expected much greater differences between the two, given that Orrorin is twice as old,” Dr. Richmond said.

An accompanying article in the journal quoted Dr. Pickford and Dr. Senut as being pleased to have confirmation that their fossil species was bipedal, but did not back off from their insistence that other aspects of the skeleton showed its closer resemblance to much later Homo.

Other scientists agreed that the findings seemed to confirm Orrorin was indeed an early ancestor of humans and not more closely linked to apes, as had been argued by critics.

In light of the new research, Dr. Richmond said, Orrorin not only was a “basal member” of the human family but also had walking mechanics that went largely unchanged until the rise of Homo, especially in Homo erectus less than two million years ago.

More recent fossil discoveries, in Chad, have apparently revealed a protohuman species even more primitive than Orrorin. The species, Sahelanthropus tchadensis, is estimated to have lived close to seven million years ago, which is thought to be when the human and chimpanzee lineages diverged from a common ancestor. But the fossils from Chad, mainly a single skull, are too fragmentary for scientists to establish whether this species also walked on two legs.

http://www.nytimes.com/2008/03/21/science/21bone.html
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Ancient 'Out Of Africa' Migration Left Stamp On European Genetic Diversity by coldrum on Tuesday, 20 May 2008
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Ancient 'Out Of Africa' Migration Left Stamp On European Genetic Diversity

Human migration from Africa to Europe more than 30,000 years ago appears to have left a mark on the genes of Europeans today.

A Cornell-led study, reported in the Feb. 21 issue of the journal Nature, compared more than 10,000 sequenced genes from 15 African-Americans and 20 European-Americans. The results suggest that European populations have proportionately more harmful variations, though it is unclear what effects these variations actually may have on the overall health of Europeans.

Computer simulations suggest that the first Europeans comprised small and less diverse populations. That would have allowed mildly harmful genetic variations within those populations to become more frequent over time, the researchers report.

"What we may be seeing is a 'population genetic echo' of the founding of Europe," said Carlos Bustamante, assistant professor of biological statistics and computational biology at Cornell and senior co-author with Andrew Clark, a professor of molecular biology and genetics.

"Since we tend to think of European populations as quite large, we did not expect to see a significant difference in the distribution of neutral and deleterious variation between the two populations," said Bustamante. "It was quite surprising, but when we cross-checked our results to data sets gathered by other groups, we found the same trend."

The researchers focused on single nucleotide polymorphisms (SNPs), where a single DNA base pair (the smallest structural unit) in a gene's sequence had been altered. Genetic variations were classified as to whether a SNP was found in one or both populations. Some of these genetic changes led to amino acid changes in the proteins that the genes express, while others had no effect.

Collaborators at Max Planck Institute in Tübingen, Germany, and Harvard Medical School analyzed the amino acid changes and used a computer algorithm to predict whether the changes alter a protein's structure or function, and classified the changes into three categories: benign, possibly damaging or probably damaging.

Using that information, the Cornell group found that the European sample, while showing overall less genetic variation, had proportionately more amino acid changes and proportionately more harmful amino acid single nucleotide polymorphisms than the African sample.

"It's difficult to tell what the precise impact that a higher proportion of deleterious single nucleotide polymorphisms in the population will have on the average person's health," said Kirk Lohmueller, a graduate student in both Bustamante's and Clark's labs and the paper's lead author. "More detailed studies that involve sequencing many individuals both with and without certain diseases would better enable us to get at this question."

Future research may also reveal similar signatures as other populations left Africa for other geographic destinations.

Other Cornell co-authors include Amit Indap, Adam Boyko and Ryan Hernandez as well as Rasmus Nielsen, a former Cornell faculty member now at the University of Copenhagen, and Melissa Hubisz, a former Cornell programmer now at the University of Chicago. Celera Diagnostics performed the gene sequences.

The study was funded by the National Institutes of Health and National Science Foundation.

http://www.sciencedaily.com/releases/2008/02/080220132608.htm
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Migration of Early Humans From Africa Aided By Wet Weather by coldrum on Wednesday, 17 October 2007
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Migration of Early Humans From Africa Aided By Wet Weather

The African origin of early modern humans 200,000--150,000 years ago is now well documented, with archaeological data suggesting that a major migration from tropical east Africa to the Levant took place between 130,000 and 100,000 years ago via the presently hyper-arid Saharan-Arabian desert.
This migration was dependent on the occurrence of wetter climate in the region. Whereas there is good evidence that the southern and central Saharan-Arabian desert experienced increased monsoon precipitation during this period, no unequivocal evidence has been found for a corresponding rainfall increase in the northern part of the migration corridor, including the Sinai-Negev land bridge between Africa and Asia.

Passage through this "bottleneck" region would have been dependent on the development of suitable climate conditions.

Vaks et al. present a reconstruction of paleoclimate in the Negev Desert based on absolute uranium series dating of carbonate cave deposits (speleothems). Speleothems only form when rainwater enters the groundwater system and vegetation grows above a cave.

Today the climate in the Negev Desert is very arid and speleothems do not form, but their presence in a number of caves clearly indicates that conditions were wetter in the past. Vaks et al. dated 33 speleothem samples from five caves in the central and southern Negev Desert.

The ages of these speleothems show that the last main period of increased rainfall occurred between 140,000 and 110,000 years ago. The climate during this time consisted of episodic wet events that enabled the deserts of the northeastern Sahara, Sinai, and the Negev to become more hospitable for the movement of early modern humans.

The simultaneous occurrence of wet periods in the northern and southern parts of Saharan-Arabian desert could have led to the disappearance of the desert barrier between central Africa and the Levant.

The humid period in the Negev Desert between 140,000 and 110,000 years ago was preceded and followed by essentially unbroken arid conditions; thus creating a climatic "window" for early modern human migration to the Levant. Vaks et al.'s study suggest that climate change had an important limiting role in the timing of dispersal of early modern humans out of Africa.

http://www.sciencedaily.com/releases/2007/08/070828155004.htm
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Handsome By Chance: Why Humans Look Different From Neanderthals by coldrum on Thursday, 23 August 2007
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Chance, not natural selection, best explains why the modern human skull looks so different from that of its Neanderthal relative, according to a new study led by Tim Weaver, assistant professor of anthropology at UC Davis.
"For 150 years, scientists have tried to decipher why Neanderthal skulls are different from those of modern humans," Weaver said. "Most accounts have emphasized natural selection and the possible adaptive value of either Neanderthal or modern human traits. We show that instead, random changes over the past 500,000 years or so – since Neanderthals and modern humans became isolated from each other – are the best explanation for these differences."

Weaver and his colleagues compared cranial measurements of 2,524 modern human skulls and 20 Neanderthal specimens, then contrasted those results with genetic information from a separate sample of 1,056 modern humans.

The scientists concluded that Neanderthals did not develop their protruding mid-faces as an...

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Early Modern Human Skull Includes Surprising Neanderthal Feature by coldrum on Thursday, 23 August 2007
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Early Modern Human Skull Includes Surprising Neanderthal Feature

In 1942, a human braincase was found in Romania during phosphate mining. The skull’s geological age has remained uncertain. Now, new radiocarbon analysis appearing in the August issue of Current Anthropology directly dates the skull to approximately 33,000 years ago, placing it in the Upper Paleolithic.
Though this braincase is in many ways similar to other known specimens from the period, the fossil also presents a distinctly Neanderthal feature, ubiquitous among Neanderthals, extremely rare among archaic humans, and unknown among prior modern humans.

“The mosaic is most parsimoniously explained as the result of a modest level of admixture with [Neanderthals] as modern humans dispersed across Europe,” write Andrei Soficaru (Institutul de Anthropologie, Romania), Catalin Petrea (Institutul de Speologie, Romania), Adiran Dobos (Institutl de Arheologie, Romania), and Erik Trinkaus (Washington University, St....

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Fossils paint messy picture of human origins by coldrum on Thursday, 23 August 2007
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Fossils paint messy picture of human origins

New findings raise questions about who evolved from whom.

Surprising fossils dug up in Africa are creating messy kinks in the iconic straight line of human evolution with its knuckle-dragging ape and briefcase-carrying man.

The new research by famed paleontologist Meave Leakey in Kenya shows our family tree is more like a wayward bush with stubby branches, calling into question the evolution of our ancestors.

The old theory was that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became us, Homo sapiens. But those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years, Leakey and colleagues report in a paper published in Thursday’s issue of the journal Nature.

In 2000 Leakey found an old H. erectus complete skull within walking distance of an upper jaw of the H. habilis, and both dated from the same general...

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