Thursday, 7 January 2010

We are the eyes of Gaia

And we are sharpening our vision. Seeking for the truth, is there other life in this Universe...
Let´s wait and see...
Here goes de new.

We could find Earth-like planets soon

Thu Jan 7, 5:09 pm ET
WASHINGTON – Astronomers say they are on the verge of finding planets like Earth orbiting other stars, a key step in determining if we are alone in the universe.

A top NASA official and other leading scientists say that within four or five years they should discover the first Earth-like planet where life could develop, or may have already. A planet close to the size of Earth could even be found sometime this year if preliminary hints from a new space telescope pan out.

At the annual American Astronomical Society conference this week, each discovery involving so-called "exoplanets" — those outside our solar system — pointed to the same conclusion: Quiet planets like Earth where life could develop probably are plentiful, despite a violent universe of exploding stars, crushing black holes and colliding galaxies.

NASA's new Kepler telescope and a wealth of new research from the suddenly hot and competitive exoplanet field generated noticeable buzz at the convention. Scientists are talking about being at "an incredible special place in history" and closer to answering a question that has dogged humanity since the beginning of civilization.

"The fundamental question is: Are we alone? For the first time, there's an optimism that sometime in our lifetimes we're going to get to the bottom of that," said Simon "Pete" Worden, an astronomer who heads NASA's Ames Research Center. "If I were a betting man, which I am, I would bet we're not alone — there is a lot of life."

Even the Roman Catholic Church has held scientific conferences about the prospect of extraterrestrial life, including a meeting last November.

"These are big questions that reflect upon the meaning of the human race in the universe," the director of the Vatican Observatory, the Rev. Jose Funes, said Wednesday in an interview at this week's conference.

Worden told The Associated Press: "I would certainly expect in the next four or five years we'd have an Earth-sized planet in the habitable zone."

Worden's center runs the Kepler telescope, which is making an intense planetary census of a small portion of the galaxy.

Unlike the Hubble Space Telescope, which is a general instrument, Kepler is a specialized telescope just for planet-hunting. Its sole instrument is a light meter that measures the brightness of more than 100,000 stars simultaneously, watching for anything that causes a star to dim. That dimming is often a planet passing in front of the star.

Any planet that could support life would almost certainly need to be rocky rather than gaseous. And it would need to be in just the right location. Planets that are too close to their star will be too hot, and those too far away are too cold.

"Every single rock we turn over, we find a planet," said Ohio State University astronomer Scott Gaudi. "They occur in all sorts of environments, all sorts of places."

Researchers are finding exoplanets at a dizzying pace. In the 1990s, astronomers found a couple of new planets a year. For most of the last decade, it was up to a couple of planets every month.

This year, planets are being found on about a daily basis, thanks to the Kepler telescope. The number of discovered exoplanets is now well past 400. But none of those has the right components for life.

That's about to change, say the experts.

"From Kepler, we have strong indications of smaller planets in large numbers, but they aren't verified yet," said Geoff Marcy of the University of California at Berkeley. He is one of the founding fathers of the field of planet-hunting and a Kepler scientist.

But there is a big caveat. Most of the early exoplanet candidates found by Kepler are turning out to be something other than a planet, such as another star crossing the telescope's point of view, when double- and triple-checked, said top Kepler scientist Bill Borucki.

Kepler is concentrating on about one-four hundredth of the nighttime sky, scanning more than 100,000 stars, ranging from a few hundred to a few thousand light years away. A light year is about 5.9 trillion miles. So such planets are too far to travel to, and they cannot be viewed directly like the planets in our solar system.

If there were an Earth-like body in the area Kepler is searching, the telescope would find it, Marcy said. But it can take three years to confirm a planet's orbital path.

What Kepler has confirmed so far keeps pointing to the idea that there are many other Earths. Before Kepler, those bodies were too small to be seen. Borucki this week announced the finding of five new exoplanets — all discovered in just the first six weeks of planet-hunting. But all those planets were too large and in the wrong place to be like Earth.

When Kepler looked at 43,000 stars that are about the same size as our sun, it found that about two-thirds of them appeared to be as life-friendly and nonviolent as our nearest star.

Marcy, who this week announced finding a planet just four times larger than Earth, does not like to speculate how many stars have Earth-like planets. But when pressed, he said Thursday: "70 percent of all stars have rocky planets."

"If you are in the kitchen and are trying to cook up a habitable planet, we already know that in the cosmos, all the ingredients are there," he said.

While astronomers at the convention are excited about exoplanets, Marcy is more skeptical, as is Jill Tarter, director of the SETI Institute, which seeks out intelligent life by monitoring for electromagnetic transmissions. They said there is still the chance that the searches can come up empty.

Marcy said there is the small possibility that planets do not form easily at Earth's size, and that most are bigger.

Tarter — who was the basis for a character portrayed in the movie "Contact" by Jodie Foster — said: "I always worry that we talk ourselves into thinking we know more than we know."

Once an Earth-like planet is found in the right place, determining if there are the ingredients for life there will pose another hurdle.

It will require costly new telescopes. A massive space telescope to scan Earth-like planets for oxygen, water, carbon dioxide — and even faint signs of industrial emissions from civilization — would cost about $5 billion.

For now, such a high price is a budget-buster, but that could change. Cornell University astronomer Martha Haynes said: "We are at a very special moment in the history of mankind."


On the Net:

NASA's Kepler Telescope:

NASA's Exoplanet Exploration Program:

The Extrasolar Planets Encyclopaedia:

American Astronomical Society:

Sunday, 25 October 2009

Snakes helped us to sharpen our vision

By Kenneth Kidd
The need to detect snakes may have given humans an evolutionary nudge toward developing better vision.
When Eve encountered a certain serpent and was bedazzled into eating fruit from the Tree of Knowledge, nothing nice ensued. In the Old Testament, nothing nice ever ensued when God's wrath was aroused.

So while Eve's eyes were, indeed opened, the whole episode ensured a life of toil for Adam and billions of painful childbirths for all women to come.

It now turns out that key elements of that story – serpent, fruit, vision and the large-headed babies that are the proximate cause of painful births – may have played similarly crucial roles in key stages of human evolution, with somewhat more generous results.

Lynne Isbell, a professor of anthropology and animal behaviour at the University of California at Davis (UCD), contends that snakes lie at the root of what makes humans, well, human.

It's a complex thesis, relying on everything from fossil records and primate behaviour to palaeogeography and modern advances in neuroscience. But at the risk of doing violence to that complexity, the essential argument is this:

The earliest predators of our mammal ancestors were snakes, especially constrictors, and venomous snakes can be equally lethal, even when striking defensively. Over the course of millions of years, the need to detect snakes thus gave an evolutionary nudge toward developing better vision.

So for some animals, sight started to become more important than a sense of smell. Better vision, in turn, made it easier for our ancestors to pick out fruits that were ripe, and therefore rich in glucose. We can distinguish reds and oranges from greens.

Through neuroscience, we now know that a vast amount of the human brain is connected to vision, and we also know that glucose is crucial to brain development. Combine the two over millennia, and you end up with today's (painfully) big-headed babies.

Earlier this week, the Star spoke with Isbell, whose book, The Fruit, The Tree and The Serpent, has just been published. The following are edited excerpts from that conversation.

What made you suspect that snakes played such a key role in human evolution?

I was actually looking at a different question: Why is it that female primates in the New World (South America and Central America) are so willing to leave their home areas when there's a heavy cost to leaving. You're more susceptible to predation. But in the Old World, monkeys don't do that. The females stay put.

In my own experience (in Africa), leopards had just decimated the groups of monkeys that I studied in two different places. I started to look at, when did (large predatory) cats get to the New World compared with the Old World?

We know that constrictors are predators of primates, too, so when did constrictors get to the New World?

And it turns out that, not only did constrictors and venomous snakes evolve much earlier than leopards and raptors, they've co-existed with Old World primates for much longer.

They had this bio-geographical relationship with primates that sort of fit with what I knew then to be differences in their visual systems.

In that Old World primates have more advanced vision?

All I knew at the time was that there was a difference is colour vision and the degrees of visual acuity.

There have been other theories about why primates developed better vision, but yours seems to be the first to identify the key role of snakes and to rely heavily on neuroscience. Do you expect neuroscience to start playing a bigger role in answering other evolutionary questions?

It would be great if there could be dialogue back and forth. If people from different disciplines could get together and talk, I think we could make some pretty interesting advances in all fields.

It used to be that mammals were classed into orders based mostly on physical characteristics. Now molecular research is shuffling the deck based on DNA, so some of our closest relatives also include flying lemurs, treeshrews, rabbits and rats. Why didn't our non-primate cousins develop similar vision?

All mammals would have had to deal with constricting snakes, so vision would have been useful to them. But not all mammals eat the same things, to allow them to benefit from the tradeoff between vision and olfaction. If you have good vision, then you're going to lose your sense of smell to some degree.

Because of their diets, then, rabbits and rats had to rely much more on smell to locate greens and seeds?

They eat foods that plants don't want them to eat (so) plants don't evolve ways to make those types of foods smellier. It's the animals that eat fruits that wouldn't suffer any loss if their sense of smell started to get worse. They could afford to expand their vision.

You note how, whenever you're doing field research, it's always the monkeys who detect snakes before anyone else. They get very agitated and even have special alarm calls that only refer to snakes, not other predators.

Yeah. I was just talking with a grad student yesterday. She's worked in Costa Rica and she said that when she's not with the monkeys, she rarely sees snakes, but when she's there with them, she sees them almost every other day. The monkeys point them out.

How much of our fear of snakes is instinctive and how much is socialized?

That's a really good question. Since we are Old World primates ourselves, our ancestors had to deal with snakes for a long time. It's possible that if we're primed to be afraid of snakes, all it takes is for us to learn to be afraid.

Rhesus macaques are not necessarily afraid of snakes the first time they see them, but if they see another rhesus macaque reacting fearfully, then they learn to fear the snakes.

There's an evolutionary preparedness to be afraid of snakes that doesn't exist for more innocuous objects, like flowers. It's probably the same for us.

Is that why snakes figure so prominently in so many myths? Even the mighty Thor gets felled by a snake in Norse mythology.

That's what I was wondering. Why do we focus so much on snakes? Why, unless there's something deep within us, a long evolutionary association with snakes that brings it out in myths and religion.

Malawi could be the cradle of humankind

Mabvuto Banda
KARONGA, Malawi (Reuters) – The latest discovery of pre-historic tools and remains of hominids in Malawi's remote northern district of Karonga provides further proof that the area could be the cradle of humankind, a leading German researcher said.
Professor Friedemann Schrenk of the Goethe University in Frankfurt told Reuters that two students working on the excavation site last month had discovered prehistoric tools and a tooth of an hominid.
"This latest discovery of prehistoric tools and remains of hominids provides additional proof to the theory that the Great Rift Valley of Africa and perhaps the excavation site near Karonga can be considered the cradle of humankind," Schrenk said.
A hominid is a member of a family of primates which includes humans and their prehistoric ancestors.
The discovery was at Malema excavation site, 10 km (6 miles) from Karonga.
The site also contains some of the earliest dinosaurs which lived between 100 million and 140 million years ago and early hominids believed to have lived between a million and 6 million years ago.
He is leading a team of researchers from Europe and Africa to establish an African center for interdisciplinary studies on mammal and hominid evolution in the southern African nation.
Karonga is about 615 km (380 miles) north of the capital Lilongwe and is near the border with Tanzania.

Humans Still Evolving

Eben Harrell – Fri Oct 23
Modern Homo sapiens is still evolving. Despite the long-held view that natural selection has ceased to affect humans because almost everybody now lives long enough to have children, a new study of a contemporary Massachusetts population offers evidence of evolution still in action.

A team of scientists led by Yale University evolutionary biologist Stephen Stearns suggests that if the natural selection of fitter traits is no longer driven by survival, perhaps it owes to differences in women's fertility. "Variations in reproductive success still exist among humans, and therefore some traits related to fertility continue to be shaped by natural selection," Stearns says. That is, women who have more children are more likely to pass on certain traits to their progeny. (See the top 10 scientific discoveries of 2008.)

Stearns' team examined the vital statistics of 2,238 postmenopausal women participating in the Framingham Heart Study, which has tracked the medical histories of some 14,000 residents of Framingham, Mass., since 1948. Investigators searched for correlations between women's physical characteristics - including height, weight, blood pressure and cholesterol levels - and the number of offspring they produced. According to their findings, it was stout, slightly plump (but not obese) women who tended to have more children - "Women with very low body fat don't ovulate," Stearns explains - as did women with lower blood pressure and cholesterol levels. Using a sophisticated statistical analysis that controlled for any social or cultural factors that could impact childbearing, researchers determined that these characteristics were passed on genetically from mothers to daughters and granddaughters.

If these trends were to continue with no cultural changes in the town for the next 10 generations, by 2409 the average Framingham woman would be 2 cm (0.8 in) shorter, 1 kg (2.2 lb.) heavier, have a healthier heart, have her first child five months earlier and enter menopause 10 months later than a woman today, the study found. "That rate of evolution is slow but pretty similar to what we see in other plants and animals. Humans don't seem to be any exception," Stearns says.

Douglas Ewbank, a demographer at the University of Pennsylvania who undertook the statistical analysis for the study, which was published Oct. 21 in the Proceedings of the National Academy of Sciences (PNAS), says that because cultural factors tend to have a much more prominent impact than natural selection in the shaping of future generations, people tend to write off the effect of evolution. "Those changes we predict for 2409 could be wiped out by something as simple as a new school-lunch program. But whatever happens, it's likely that in 2409, Framingham women will be 2 cm shorter and 1 kg heavier than they would have been without natural selection. Evolution is a very slow process. We don't see it if we look at our grandparents, but it's there."

Other recent genetic research has backed up that notion. One study, published in PNAS in 2007 and led by John Hawks, an anthropologist at the University of Wisconsin at Madison, found that some 1,800 human gene variations had become widespread in recent generations because of their modern-day evolutionary benefits. Among those genetic changes, discovered by examining more than 3 million DNA variants in 269 individuals: mutations that allow people to digest milk or resist malaria and others that govern brain development.

But not all evolutionary changes make inherent sense. Since the Industrial Revolution, modern humans have grown taller and stronger, so it's easy to assume that evolution is making humans fitter. But according to anthropologist Peter McAllister, author of Manthropology: the Science of Inadequate Modern Man, the contemporary male has evolved, at least physically, into "the sorriest cohort of masculine Homo sapiens to ever walk the planet." Thanks to genetic differences, an average Neanderthal woman, McAllister notes, could have whupped Arnold Schwarzenegger at his muscular peak in an arm-wrestling match. And prehistoric Australian Aborigines, who typically built up great strength in their joints and muscles through childhood and adolescence, could have easily beat Usain Bolt in a 100-m dash.

Steve Jones, an evolutionary biologist at University College London who has previously held that human evolution was nearing its end, says the Framingham study is indeed an important example of how natural selection still operates through inherited differences in reproductive ability. But Jones argues that variation in female fertility - as measured in the Framingham study - is a much less important factor in human evolution than differences in male fertility. Sperm hold a much higher chance of carrying an error or mutation than an egg, especially among older men. "While it used to be that men had many children in older age to many different women, now men tend to have only a few children at a younger age with one wife. The drop in the number of older fathers has had a major effect on the rate of mutation and has at least reduced the amount of new diversity - the raw material of evolution. Darwin's machine has not stopped, but it surely has slowed greatly," Jones says. (See TIME's special report on the environment.)

Despite evidence that human evolution still functions, biologists concede that it's anyone's guess where it will take us from here. Artificial selection in the form of genetic medicine could push natural selection into obsolescence, but a lethal pandemic or other cataclysm could suddenly make natural selection central to the future of the species. Whatever happens, Jones says, it is worth remembering that Darwin's beautiful theory has suffered a long history of abuse. The bastard science of eugenics, he says, will haunt humanity as long as people are tempted to confuse evolution with improvement. "Uniquely in the living world, what makes humans what we are is in our minds, in our society, and not in our evolution," he says.

Wednesday, 14 October 2009

Modern man a wimp says anthropologist

Tue Oct 13, 2009
By John Mehaffey
LONDON (Reuters) - Many prehistoric Australian aboriginals could have outrun world 100 and 200 meters record holder Usain Bolt in modern conditions.

Some Tutsi men in Rwanda exceeded the current world high jump record of 2.45 meters during initiation ceremonies in which they had to jump at least their own height to progress to manhood.

Any Neanderthal woman could have beaten former bodybuilder and current California governor Arnold Schwarzenegger in an arm wrestle.

These and other eye-catching claims are detailed in a book by Australian anthropologist Peter McAllister entitled "Manthropology" and provocatively sub-titled "The Science of the Inadequate Modern Male."

McAllister sets out his stall in the opening sentence of the prologue.

"If you're reading this then you -- or the male you have bought it for -- are the worst man in history.

"No ifs, no buts -- the worst man, period...As a class we are in fact the sorriest cohort of masculine Homo sapiens to ever walk the planet."

Delving into a wide range of source material McAllister finds evidence he believes proves that modern man is inferior to his predecessors in, among other fields, the basic Olympic athletics disciplines of running and jumping.

His conclusions about the speed of Australian aboriginals 20,000 years ago are based on a set of footprints, preserved in a fossilized claypan lake bed, of six men chasing prey.


An analysis of the footsteps of one of the men, dubbed T8, shows he reached speeds of 37 kph on a soft, muddy lake edge. Bolt, by comparison, reached a top speed of 42 kph during his then world 100 meters record of 9.69 seconds at last year's Beijing Olympics.

In an interview in the English university town of Cambridge where he was temporarily resident, McAllister said that, with modern training, spiked shoes and rubberized tracks, aboriginal hunters might have reached speeds of 45 kph.

"We can assume they are running close to their maximum if they are chasing an animal," he said.

"But if they can do that speed of 37 kph on very soft ground I suspect there is a strong chance they would have outdone Usain Bolt if they had all the advantages that he does.

"We can tell that T8 is accelerating toward the end of his tracks."

McAllister said it was probable that any number of T8's contemporaries could have run as fast.

"We have to remember too how incredibly rare these fossilizations are," he said. "What are the odds that you would get the fastest runner in Australia at that particular time in that particular place in such a way that was going to be preserved?"

Turning to the high jump, McAllister said photographs taken by a German anthropologist showed young men jumping heights of up to 2.52 meters in the early years of last century.


"It was an initiation ritual, everybody had to do it. They had to be able to jump their own height to progress to manhood," he said.

"It was something they did all the time and they lived very active lives from a very early age. They developed very phenomenal abilities in jumping. They were jumping from boyhood onwards to prove themselves."

McAllister said a Neanderthal woman had 10 percent more muscle bulk than modern European man. Trained to capacity she would have reached 90 percent of Schwarzenegger's bulk at his peak in the 1970s.

"But because of the quirk of her physiology, with a much shorter lower arm, she would slam him to the table without a problem," he said.

Manthropology abounds with other examples:

* Roman legions completed more than one-and-a-half marathons a day carrying more than half their body weight in equipment.

* Athens employed 30,000 rowers who could all exceed the achievements of modern oarsmen.

* Australian aboriginals threw a hardwood spear 110 meters or more (the current world javelin record is 98.48).

McAllister said it was difficult to equate the ancient spear with the modern javelin but added: "Given other evidence of Aboriginal man's superb athleticism you'd have to wonder whether they couldn't have taken out every modern javelin event they entered."

Why the decline?

"We are so inactive these days and have been since the industrial revolution really kicked into gear," McAllister replied. "These people were much more robust than we were.

"We don't see that because we convert to what things were like about 30 years ago. There's been such a stark improvement in times, technique has improved out of sight, times and heights have all improved vastly since then but if you go back further it's a different story.

"At the start of the industrial revolution there are statistics about how much harder people worked then.

"The human body is very plastic and it responds to stress. We have lost 40 percent of the shafts of our long bones because we have much less of a muscular load placed upon them these days.

"We are simply not exposed to the same loads or challenges that people were in the ancient past and even in the recent past so our bodies haven't developed. Even the level of training that we do, our elite athletes, doesn't come close to replicating that.

"We wouldn't want to go back to the brutality of those days but there are some things we would do well to profit from."

(Editing by Clare Fallon; To query or comment on this story email
Can Evolution Run in Reverse? A Study Says It’s a One-Way Street
Evolutionary biologists have long wondered if history can run backward. Is it possible for the proteins in our bodies to return to the old shapes and jobs they had millions of years ago?
Examining the evolution of one protein, a team of scientists declares the answer is no, saying new mutations make it practically impossible for evolution to reverse direction. “They burn the bridge that evolution just crossed,” said Joseph W. Thornton, a biology professor at the University of Oregon and co-author of a paper on the team’s findings in the current issue of Nature.
The Belgian biologist Louis Dollo was the first scientist to ponder reverse evolution. “An organism never returns to its former state,” he declared in 1905, a statement later dubbed Dollo’s law.
To see if he was right, biologists have reconstructed evolutionary history. In 2003, for example, a team of scientists studied wings on stick insects. They found that the insects’ common ancestor had wings, but some of its descendants lost them. Later, some of those flightless insects evolved wings again.
Yet this study did not necessarily refute Dollo’s law. The stick insects may indeed have evolved a new set of wings, but it is not clear whether this change appeared as reverse evolution at the molecular level. Did the insects go back to the exact original biochemistry for building wings, or find a new route, essentially evolving new proteins?
Dr. Thornton and his colleagues took a close look at the possibility of reverse evolution at this molecular level. They studied a protein called a glucocorticoid receptor that helps humans and most other vertebrates cope with stress by grabbing a hormone called cortisol and then switching on stress-defense genes.
By comparing the receptor to related proteins, the scientists reconstructed its history. Some 450 million years ago, it started out with a different shape that allowed it to grab tightly to other hormones, but only weakly to cortisol. Over the next 40 million years, the receptor changed shape, so that it became very sensitive to cortisol but could no longer grab other hormones.
During those 40 million years, Dr. Thornton found, the receptor changed in 37 spots, only 2 of which made the receptor sensitive to cortisol. Another 5 prevented it from grabbing other hormones. When he made these 7 changes to the ancestral receptor, it behaved just like a new glucocorticoid receptor.
Dr. Thornton reasoned that if he carried out the reverse operation, he could turn a new glucocorticoid receptor into an ancestral one. So he and his colleagues reversed these key mutations to their old form.
To Dr. Thornton’s surprise, the experiment failed. “All we got was a completely dead receptor,” he said.
To figure out why they could go forward but not backward, Dr. Thornton and his colleagues looked closely again at the old and new receptors. They discovered five additional mutations that were crucial to the transition. If they reversed these five mutations as well, the new receptor behaved like an old one.
Based on these results, Dr. Thornton and his colleagues concluded that the evolution of the receptor unfolded in two chapters. In the first, the receptor acquired the seven key mutations that made it sensitive to cortisol and not to other hormones. In the second, it acquired the five extra mutations, which Dr. Thornton called “restrictive” mutations.
These restrictive mutations may have fine-tuned how the receptor grabbed cortisol. Or they may have had no effect at all. In either case, these five mutations added twists and tails to the receptor. When Dr. Thornton tried to return the receptor to its original form, these twists and tails got in the way.
Dr. Thornton argues that once the restrictive mutations evolved, they made it practically impossible for the receptor to evolve back to its original form. The five key mutations could not be reversed first, because the receptor would be rendered useless. Nor could the seven restrictive mutations be reversed first. Those mutations had little effect on how the receptor grabbed hormones. So there was no way that natural selection could favor individuals with reversed mutations.
For now it is an open question whether other proteins have an equally hard time evolving backward. But Dr. Thornton suspects they do.
“I would never say evolution is never reversible,” Dr. Thornton said. But he thinks it can only go backward when the evolution of the trait is simple, like when a single mutation is involved. When new traits are produced by several mutations that influence one another, he argues, that complexity shuts off reverse evolution. “We know that kind of complexity is very common,” he said.
If this molecular Dollo’s law holds up, Dr. Thornton believes it says something important about the course of evolutionary history. Natural selection can achieve many things, but it is hemmed in. Even harmless, random mutations can block its path.
“The biology we ended up with was not inevitable,” he said. “It was just one roll of the evolutionary dice.”
Source: New York Times Sep 29 2009

Thursday, 1 October 2009

Our oldest ancestror found

Before Lucy came Ardi, new earliest hominid found
Randolph E. Schmid, Ap Science Writer
WASHINGTON – The story of humankind is reaching back another million years as scientists learn more about "Ardi," a hominid who lived 4.4 million years ago in what is now Ethiopia. The 110-pound, 4-foot female roamed forests a million years before the famous Lucy, long studied as the earliest skeleton of a human ancestor.

This older skeleton reverses the common wisdom of human evolution, said anthropologist C. Owen Lovejoy of Kent State University.

Rather than humans evolving from an ancient chimp-like creature, the new find provides evidence that chimps and humans evolved from some long-ago common ancestor — but each evolved and changed separately along the way.

"This is not that common ancestor, but it's the closest we have ever been able to come," said Tim White, director of the Human Evolution Research Center at the University of California, Berkeley.

The lines that evolved into modern humans and living apes probably shared an ancestor 6 million to 7 million years ago, White said in a telephone interview.

But Ardi has many traits that do not appear in modern-day African apes, leading to the conclusion that the apes evolved extensively since we shared that last common ancestor.

A study of Ardi, under way since the first bones were discovered in 1994, indicates the species lived in the woodlands and could climb on all fours along tree branches, but the development of their arms and legs indicates they didn't spend much time in the trees. And they could walk upright, on two legs, when on the ground.

Formally dubbed Ardipithecus ramidus — which means root of the ground ape — the find is detailed in 11 research papers published Thursday by the journal Science.

"This is one of the most important discoveries for the study of human evolution," said David Pilbeam, curator of paleoanthropology at Harvard's Peabody Museum of Archaeology and Ethnology.

"It is relatively complete in that it preserves head, hands, feet and some critical parts in between. It represents a genus plausibly ancestral to Australopithecus — itself ancestral to our genus Homo," said Pilbeam, who was not part of the research teams.

Scientists assembled the skeleton from 125 pieces.

Lucy, also found in Africa, thrived a million years after Ardi and was of the more human-like genus Australopithecus.

"In Ardipithecus we have an unspecialized form that hasn't evolved very far in the direction of Australopithecus. So when you go from head to toe, you're seeing a mosaic creature that is neither chimpanzee, nor is it human. It is Ardipithecus," said White.

White noted that Charles Darwin, whose research in the 19th century paved the way for the science of evolution, was cautious about the last common ancestor between humans and apes.

"Darwin said we have to be really careful. The only way we're really going to know what this last common ancestor looked like is to go and find it. Well, at 4.4 million years ago we found something pretty close to it," White said. "And, just like Darwin appreciated, evolution of the ape lineages and the human lineage has been going on independently since the time those lines split, since that last common ancestor we shared."

Some details about Ardi in the collection of papers:

• Ardi was found in Ethiopia's Afar Rift, where many fossils of ancient plants and animals have been discovered. Findings near the skeleton indicate that at the time it was a wooded environment. Fossils of 29 species of birds and 20 species of small mammals were found at the site.

• Geologist Giday WoldeGabriel of Los Alamos National Laboratory was able to use volcanic layers above and below the fossil to date it to 4.4 million years ago.

• Ardi's upper canine teeth are more like the stubby ones of modern humans than the long, sharp, pointed ones of male chimpanzees and most other primates. An analysis of the tooth enamel suggests a diverse diet, including fruit and other woodland-based foods such as nuts and leaves.

• Paleoanthropologist Gen Suwa of the University of Tokyo reported that Ardi's face had a projecting muzzle, giving her an ape-like appearance. But it didn't thrust forward quite as much as the lower faces of modern African apes do. Some features of her skull, such as the ridge above the eye socket, are quite different from those of chimpanzees. The details of the bottom of the skull, where nerves and blood vessels enter the brain, indicate that Ardi's brain was positioned in a way similar to modern humans, possibly suggesting that the hominid brain may have been already poised to expand areas involving aspects of visual and spatial perception.

• Ardi's hand and wrist were a mix of primitive traits and a few new ones, but they don't include the hallmark traits of the modern tree-hanging, knuckle-walking chimps and gorillas. She had relatively short palms and fingers which were flexible, allowing her to support her body weight on her palms while moving along tree branches, but she had to be a careful climber because she lacked the anatomical features that allow modern-day African apes to swing, hang and easily move through the trees.

• The pelvis and hip show the gluteal muscles were positioned so she could walk upright.

• Her feet were rigid enough for walking but still had a grasping big toe for use in climbing.

The research was funded by the National Science Foundation, the Institute of Geophysics and Planetary Physics of the University of California, Los Alamos National Laboratory, the Japan Society for the Promotion of Science and others.

Ardi, Humans and Primates
Between present humans and our earliest prehuman ancestor, there is a direct genetic and evolutionary link, a clear map of descent that includes the earliest common ancestors we share with other primates. We just don’t know what it looks like yet. Whether paleontologists will ever be able to fill in all the details on that map depends on discoveries like one made by a team of scientists led by Tim D. White from the University of California, Berkeley — the fossils of a species called Ardipithecus ramidus, or Ardi for short.

According to a report in the journal Science, Ardi pushes the hominid story back to 4.4 million years ago and to a site in the Afar Rift region of Ethiopia. She (the most complete skeleton is probably female) also pushes the human story into a different ecosystem than Australopithecus, the grassland ancestor who lived, in various subspecies, as long as 3.7 million years ago. Ardi, who was discovered in 1992, lived in a “woodland with small patches of forest,” a discovery that downplays the importance of open grassland to human evolution.

Like Australopithecus, she walked upright without most of the characteristic postures of chimpanzees and gorillas. Her skull is smaller than Australopithecus, about the same size as that of a bonobo.

Paleontologists are not looking for a “missing link” between humans and present-day primates closest to us — gorillas, chimpanzees and bonobos. What they’re hoping to find is the earliest common ancestor from which the separate lines of development leading to humans and modern great apes emerged. Ardi is not that common ancestor. If anything, this find helps demonstrate how quickly early hominids moved down a separate path of evolution. It also suggests that living primates do not represent some primitive stage of a shared ancestry but are, as the scientists write, “highly specialized, but through very different evolutionary pathways.”

These are tremendously important discoveries, recasting the story of hominid evolution and making us eager for the next chapter.
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