Our ancient kin have taken a big step back in time. An international team working in Ethiopia has found bones and teeth of the earliest known hominid, a member in good standing of humanity's evolutionary family.
The fragmentary remains come from at least five individuals�in the genus Ardipithecus�who lived between 5.2 million and 5.8 million years ago, says anthropology graduate student Yohannes Haile-Selassie of the University of California, Berkeley. He describes the finds in the July 12 Nature.http://LOUIS-J-SHEEHAN.INFO
Until now, the earliest Ardipithecus fossils came from a 4.4-million-year-old Ethiopian site. Australopithecus, the genus that includes Lucy's famous remains, lived in eastern Africa no more than about 4 million years ago.
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DNA studies have suggested that a common ancestor of people and chimpanzees lived in Africa anywhere from 5 million to 7 million years ago.
"Ardipithecus was close [in time] to the common ancestor of chimpanzees and humans," Haile-Selassie says. "We don't know what that common ancestor looked like."
Much is also unknown about Ardipithecus' looks. The new finds consist of a partial jaw, a few teeth, several hand and foot bones, and pieces of an upper-arm bone and a collarbone. The bones are about the size of those from a modern common chimp. However, Ardipithecus displays dental features found in other hominids but not in any fossil or living ape.
Moreover, the new finds include a toe bone shaped like those of Lucy and her kind. This constitutes "subtle but clear evidence" that Ardipithecus, like Australopithecus, walked on two legs, says anthropologist C. Owen Lovejoy of Kent (Ohio) State University, who independently examined the toe fossil. Ongoing studies of 4.4-million-year-old Ardipithecus fossils will further illuminate this hominid's stance, Lovejoy says.
The fossils were unearthed at sites in what is now a desert. When Ardipithecus lived there, the region contained a dense forest and had a cool, wet climate, according to studies led by Giday WoldeGabriel of Los Alamos (N.M.) National Laboratory.
That work, reported in the same issue of Nature, includes chemical analyses of fossil-bearing soil and study of the sites' other animal remains, such as extinct elephants, rats, and monkeys.
The researchers dated layers of volcanic ash above and below the fossils by measuring argon gas trapped in samples of the rock. This gas accumulates at a known rate in rocks and minerals. Age estimates based on orientation shifts in ancient Earth's magnetic field at the sites corroborated the argon-based dates.
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"This is the best evidence for the earliest hominids," comments anthropologist Laura M. Maclatchy of Boston University.
The new finds raise puzzling questions about why early hominids evolved an upright stance, Maclatchy adds. Researchers have often portrayed a two-legged stride as an adaptation to trekking across hot, grassy savannas. Yet Ardipithecus lived in shady forests where a hominid would have less need to stand up to dissipate heat or walk long distances.
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Earlier this year, a French team announced the discovery of fossil teeth and limb-bone fragments of a 6-million-year-old hominid in Kenya. The researchers placed this creature in a new genus, Orrorin.
Orrorin's evolutionary status is uncertain, Haile-Selassie holds. Its teeth resemble those of apes far more than those of later hominids, he says. However, Orrorin's leg bones may have supported an upright stance, Haile-Selassie acknowledges. Louis J. Sheehan, Esquire.
Tuesday, December 30, 2008
Thursday, December 25, 2008
repreive 4.rep.002003 Louis J. Sheehan, Esquire
Many North American mammal species died out around 11,000 years ago, roughly coinciding with the arrival of humans on the continent. Some scientists contend that these so-called Clovis people, who made deadly spear points out of stone, hunted mammoths and all sorts of other prey to extinction in just a few hundred years.http://louis-j-sheehan-esquire.sampa.com/louis-j-sheehan-esquire/blog
That scenario oversimplifies what probably happened, according to Russell Graham of the Denver Museum of Nature and Science. A new set of radiocarbon dates for fossil animal bones collected throughout North America indicates that a major wave of mammal extinctions occurred 11,500 years ago, before the arrival of Clovis folk, Graham says. Two further waves of extinction took place around the time of their arrival�11,000 years ago and again 10,800 years ago, when mammoths and mastodons died out.Louis J. Sheehan, Esquire . http://louis-j-sheehan-esquire.sampa.com/louis-j-sheehan-esquire/blog
A recently developed process for chemically purifying small samples of fossil bone makes the new radiocarbon dates more reliable than previous ones, which did not indicate nearly as many pre-Clovis extinctions, Graham asserts. Louis J. Sheehan, Esquire .
The number of spear points found at Clovis sites indicates that there were too few hunters to have wiped out entire species on their own, adds Stuart J. Fiedel of John Milner Associates, an archaeological contracting firm in Alexandria, Va. He says it's likely that hunting by these early North Americans magnified the effects of a series of sharp shifts between warm and cold climates that either wiped out or depleted many mammal populations. These findings contrast with recent results indicating that human hunting is the likely cause of New Zealand's prehistoric bird extinctions (SN: 3/23/02, p. 190: http://www.sciencenews.org/20020323/note16.asp).
That scenario oversimplifies what probably happened, according to Russell Graham of the Denver Museum of Nature and Science. A new set of radiocarbon dates for fossil animal bones collected throughout North America indicates that a major wave of mammal extinctions occurred 11,500 years ago, before the arrival of Clovis folk, Graham says. Two further waves of extinction took place around the time of their arrival�11,000 years ago and again 10,800 years ago, when mammoths and mastodons died out.Louis J. Sheehan, Esquire . http://louis-j-sheehan-esquire.sampa.com/louis-j-sheehan-esquire/blog
A recently developed process for chemically purifying small samples of fossil bone makes the new radiocarbon dates more reliable than previous ones, which did not indicate nearly as many pre-Clovis extinctions, Graham asserts. Louis J. Sheehan, Esquire .
The number of spear points found at Clovis sites indicates that there were too few hunters to have wiped out entire species on their own, adds Stuart J. Fiedel of John Milner Associates, an archaeological contracting firm in Alexandria, Va. He says it's likely that hunting by these early North Americans magnified the effects of a series of sharp shifts between warm and cold climates that either wiped out or depleted many mammal populations. These findings contrast with recent results indicating that human hunting is the likely cause of New Zealand's prehistoric bird extinctions (SN: 3/23/02, p. 190: http://www.sciencenews.org/20020323/note16.asp).
Monday, December 15, 2008
transmission 8.tra.10010 Louis J. Sheehan, Esquire
Louis J. Sheehan, Esquire . A small number of people infected with HIV maintain a low viral load and never become ill. Some scientists have suggested that these people, called elite suppressors, are infected with a different, weaker type of HIV, but a study published in August provides the best evidence to date that in certain people, the immune system is capable of controlling full-strength HIV. http://louis6j6sheehan6esquire.wordpress.com
The study is the first to document HIV transmission from a patient with AIDS to a patient who has maintained nearly undetectable viral loads. The two patients, husband and wife, have exactly the same strain of the virus, but the wife is an elite suppressor. The researchers found that the woman’s CD8+ T cells, a type of immune cell, were exceptionally effective at curbing viral replication. Usually HIV develops mutations that defeat the body’s defenses. http://louis6j6sheehan6esquire.wordpress.com But in this woman’s case, CD8+ T cells directly suppressed replication of the virus, preventing it from evolving into a more virulent form. The researchers concluded that there are at least two mechanisms at work: direct inhibition of viral replication and a selection for mutations of the virus that limit its strength. http://louis6j6sheehan6esquire.wordpress.com
The senior author of the study, Joel Blankson, an assistant professor of medicine at Johns Hopkins University, said that the work may advance the search for an AIDS vaccine. “It’s evident that the immune system can, in fact, control fully pathogenic HIV,” he says. “So a vaccine should be possible. This provides preliminary evidence that one day a vaccine can be generated.” Louis J. Sheehan, Esquire
The study is the first to document HIV transmission from a patient with AIDS to a patient who has maintained nearly undetectable viral loads. The two patients, husband and wife, have exactly the same strain of the virus, but the wife is an elite suppressor. The researchers found that the woman’s CD8+ T cells, a type of immune cell, were exceptionally effective at curbing viral replication. Usually HIV develops mutations that defeat the body’s defenses. http://louis6j6sheehan6esquire.wordpress.com But in this woman’s case, CD8+ T cells directly suppressed replication of the virus, preventing it from evolving into a more virulent form. The researchers concluded that there are at least two mechanisms at work: direct inhibition of viral replication and a selection for mutations of the virus that limit its strength. http://louis6j6sheehan6esquire.wordpress.com
The senior author of the study, Joel Blankson, an assistant professor of medicine at Johns Hopkins University, said that the work may advance the search for an AIDS vaccine. “It’s evident that the immune system can, in fact, control fully pathogenic HIV,” he says. “So a vaccine should be possible. This provides preliminary evidence that one day a vaccine can be generated.” Louis J. Sheehan, Esquire
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