Πέμπτη, 22 Δεκεμβρίου 2011

Mystery Of Amazonian Tribe's Head Shapes Solved

Charles Choi, LiveScience Contributor

Father and son in the wai’a ceremony at the Xavánte village of Etéñitepa. In it men try to get in contact and receive the protection of spiritual powers.
Culture may trigger rapid evolution of various human features, suggests new research into the marital practices of a tribe from the Brazilian rainforest.

Evolution is often thought to be driven by environmental factors, including climate, or geographical obstacles such as rivers and mountains. Still, cultural factors — that is, groups of traditions and behaviors passed down from one generation to another — can have profound effects on behavior and also possibly lead to evolutionary changes.

To learn more, scientists analyzed genetic, climatic, geographic and physical traits of 1,203 members of six South American tribes living in the regions of the Brazilian Amazon and highlands. Their research found that one group, the Xavánte, had significantly diverged from the others in terms of their morphology or shape, possessing larger heads, taller and narrower faces and broader noses. These characteristics evolved in the approximately 1,500 years after they split from a sister group called the Kayapó, a rate that was about 3.8-times faster than comparable rates of change seen in the other tribes.

The major changes the investigators saw apparently occurred independently of the effects of climate or geography on the Xavánte. Instead, cultural factors appear responsible. For instance, in the Xavánte village of São Domingo, a quarter of the population was made up of sons of a single chief, Apoena, who had five wives. The tribe's sexual practices allow successful men in that group to father many offspring, which in turn means that any traits of theirs can quickly dominate their population.
"We have been working with the Xavante for about half a century, and from the beginning their morphology showed differences from the classical Amerindian pattern," researcher Francisco Salzano, a geneticist at Brazil's Federal University of the Rio Grande do Sul, told LiveScience. "We verified that the Xavante experienced a remarkable pace of morphological evolution."

The researchers suggest that assembling databases of cultural and biological data could help uncover other examples of how culture might influence human evolution.

"This specific piece of research is related to a long-term project of investigation involving not only the group responsible for this paper, but many others internationally," Salzano said.

Salzano and his colleagues detailed their findings online Dec. 19 in the Proceedings of the National Academy of Sciences.

Chimps Pass On Culture Like Humans Do



Chimpanzees at Edinburgh Zoo working on a version of one of the tool-using problems included in the new studies.
CREDIT: Lewis Haughton


Chimpanzees readily learn and share techniques on how to fiddle with gadgets, new research shows, the best evidence yet that our closest living relatives pass on customs and culture just as humans do.

The new findings help shed light on the capabilities of last common ancestor of humans and chimps. And the research could also help develop better

Chimpanzees readily learn and share techniques on how to fiddle with gadgets, new research shows, the best evidence yet that our closest living relatives pass on customs and culture just as humans do.

The new findings help shed light on the capabilities of last common ancestor of humans and chimps. And the research could also help develop better robots and artificial intelligences, the researchers say.

In the wild, chimpanzee troops are often distinct from one another, possessing collections of up to 20 traditions or customary behaviors that altogether seem to form unique cultures. Such practices include various forms of tool use, including hammers and pestles; courtship rituals such as leaf-clipping, where leaves are clipped noisily with the teeth; social behaviors such as overhead hand-clasping during mutual grooming; and methods for eradicating parasites by either stabbing or squashing them.

While observing chimpanzees, evolutionary psychologist Antoine Spiteri at the University of St. Andrews in Scotland wanted to help settle the question of whether or not the apes learned such practices by watching others like humans do, as opposed to simply knowing how to perform such behaviors innately.

Spiteri and his colleagues investigated six groups of chimpanzees, each with eight to 11 apes, living in captivity in Bastrop, Texas. The researchers taught a lone chimpanzee from one group one technique for obtaining food from a complex gadget, such as stabbing food with a tool. They next taught one chimp from another group a different technique for extracting food from the same gadget, such as pushing it out down a ramp.

The extremely hot Texas weather made it hard for researchers to work, "and because participation by the chimpanzees in each of these studies has been completely voluntary, it sometimes means that we as experimenters have had to be extremely patient," Spiteri recalled. "Considering the insights we have gathered, it has been worth the sacrifice."

Over time, the researchers found each technique for tool use and food extraction spread within each group. In essence, these groups displayed their own unique culture and local traditions.

A number of these chimpanzee groups are next-door neighbors within eyeshot of each other, and researchers found traditions proved catching, with foraging practices spreading from one group to another, findings detailed in the June 19 issue of the journal Current Biology.

"The possibility that some primates may be able to learn from others has great implications on how we treat them and how we think about ourselves," Spiteri told LiveScience. "These results indicate to us that chimps have a capacity for cultural complexity, which was likely shared by our common ancestor going back around 5 million years ago."

This work is "particularly useful to robotic development and artificial intelligence," Spiteri added. "Understanding how the mechanisms of imitation and social learning can help us develop artificial beings that can behave and evolve in the way that we do and ultimately it may help us create other brains."

Existence of Uncontacted Amazon Tribe Confirmed

Home belonging to an uncontacted Indian tribe are surrounded by crops in a clearing in the Javari Valley of the western Amazon.
CREDIT: Uncontacted Amazon Indians, Javari Valley, Brazil © Peetsa/Arquivo CGIIRC-Funai
Brazilian officials have confirmed the existence of approximately 200 Indians who live in the western Amazon with no contact with the outside world.

This uncontacted tribe is not "lost" or unknown, according to tribal advocacy group Survival International. In fact, about 2,000 uncontacted Indians are suspected to live in the Javari Valley where the tribe's homes were seen from the air. But confirming the tribe's existence enables government authorities to monitor the area and protect the tribe's way of life.
In 2008, Survival International released photos of another uncontacted tribe near the Brazil-Peru border. The striking images revealed men aiming arrows skyward at the plane photographing them. Uncontacted Indian groups are aware of the outside world, a Survival International spokesperson told LiveScience at the time. But they chose to live apart, maintaining a traditional lifestyle deep in the Amazon forest. The latest images reveal that the newly confirmed tribe grows corn, peanuts, bananas and other crops.

Because the tribes are so isolated, contact with the outside world can be deadly. Survival International's website, http://www.uncontactedtribes.org/, tells the story of the uncontacted Zo'e tribe. When missionaries contacted the tribe in 1987, 45 Indians died of common diseases that they had never encountered and thus had no tolerance for, including the flu. In Peru, half of the previously uncontacted Nahua tribe died of disease after oil exploration began on their land in the 1980s.

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