Fossils may Turn 'Evolution on its Head'

This image released today by "Science"

shows the probable life appearance in

anterior view of Ardipithecus ramidus ("Ardi").

Analysis of a near-complete skeleton of a human ancestor found in Ethiopia radically changes scientists' thinking about the appearance and behavior of our earliest forebears.


Photos: Fossils may turn 'evolution on its head'

By Thomas H. Maugh II
October 1, 2009 7:30 a.m.

A treasure trove of 4.4-million-year-old fossils from the Ethiopian desert is dramatically overturning widely held ideas about the early evolution of humans and how they came to walk upright, even as it paints a remarkably detailed picture of early life in Africa, researchers reported today.

The centerpiece of the diverse collection of primate, animal and plant fossils is the near-complete skeleton of a human ancestor that demonstrates our earliest forebears looked nothing like a chimpanzee or other large primate, as is now commonly believed.

Instead, the findings suggest that the last common ancestor of humans and primates, which existed nearly 2 million years earlier, was a primitive creature that shared few traits with modern-day members of either group.

The findings, analyzed in a large group of studies published today in the journal Science, also indicate that our ancestors began walking upright in woodlands, not on grassy savannas as prior generations of researchers had speculated.

The discovery of the specimen called Ardipithecus ramidus "is one of the most important discoveries for the study of human evolution," said paleoanthropologist David Pilbeam of Harvard University, who was not involved in the research.

"The find itself is extraordinary, as were the enormous labors that went into the reconstruction of a skeleton shattered almost beyond repair," he said in an e-mailed statement."It is so rare to get a more or less complete skeleton," said paleoanthropologist Andrew Hill of Yale University. "In the entire course of human evolution, at least until you get to Neanderthals, there are only three to four available. We can always tell so much more from a skeleton" than from the jawbones and skulls that are more commonly found.

The fossils described in the new studies were found 15 years ago in the Afar Triangle of Ethiopia by a team led by paleoanthropologist Tim White of UC Berkeley. But White and his team have been relatively closemouthed about the fossils, and other researchers -- some of whom have accused him of hoarding the fossils for his own use -- have been eagerly awaiting more information.

Today, they are getting a surfeit: Eleven papers by 47 authors, and a similar number of short summaries prepared by each paper's authors.The fossils were found in a layer of sediment sandwiched between two layers of volcanic ash, each dating from 4.4 million years ago -- indicating that the fossils are also of that age.

In addition to the nearly complete fossil specimen of the female primate, which investigators have dubbed Ardi, the team found more than 100 fossils from 36 other members of the same species."These fossils are much more important than Lucy," the 3.2-million-year-old specimen of Australopithecus afarensis that was found in the Afar desert in the 1970s, said paleoanthropologist Alan Walker of Pennsylvania State University, who was not involved in the research. "The reason is that when Lucy was found, we already knew the major features of Australopithecus from fossils found in the 1940s. . . . These fossils are of a completely unknown creature, and are much stranger and more primitive than Australopithecus."

The White team also found fossils of 29 species of birds, primarily small ones like doves, lovebirds, mousebirds, passerines and swifts, as well as several that were previously unknown. Animal fossils included 20 new species of small mammals, including shrews, bats, rodents, hares and small carnivores, as well as larger animals, including baboons, colobus monkeys and spiral-horned antelopes.

Fossilized wood, seed and other plant remains indicate the presence of hackberry, fig and palm trees. Collectively, these finds indicate that the environment was more humid and cooler than it is today, and contained grassy woodland with forest patches.

Today, the Afar is a desert. But go back in a time machine and "4.4 million years ago, this was really a different world," White said. "We look up in the trees and we see that they are full of monkeys. We look around on the ground and we see that there are a lot of kudus. And we see an occasional hyena. And we see elephants and we see lots of small mammals. And we know what all of these . . . are because we have found evidence of them.

"This whole collection of data "gives us information we have never had before about human evolution," said paleoanthropologist C. Owen Lovejoy of Kent State University, one of the primary authors of the papers. "The whole savanna theory goes out the window in terms of it being the explanation for upright walking. . . . And the idea that we evolved from something like a chimpanzee also goes out the window."

Ardi stood about 47 inches tall and probably weighed 110 pounds. Many researchers had previously believed that such an early ancestor would, like modern chimps, be a knuckle-walker, using the knuckles for support while moving on all fours. Instead, Ardi appears to have climbed on all fours on branches, but walked upright on the ground. Her feet, like those of monkeys but not chimps, were designed more for propulsion than for grasping.

Her face had a projecting muzzle, giving her an ape-like appearance, but many features of her skull, such as the ridge above the eye socket, are quite different than those of chimpanzees. Her brain is about the same size as Lucy's.

Her hands lacked many of the specializations that allow modern-day African apes to swing, hang and easily move through trees. Those specializations apparently evolved in large primates after they separated from the last common ancestor with humans more than 6 million years ago. (Few fossils of such primates are available because they lived primarily in forests, which are not conducive to preservation of bone.)

The finds "are turning evolution on its head," Lovejoy said.The most controversial aspects of the papers involve the authors' -- particularly Lovejoy's -- interpretations of what the fossils say about behavior.

Of particular importance, he said, is that the sizes of males and females were about the same, and that the specimens do not have large, sharp canine teeth. Both findings suggest that the fierce, often violent competition among males for females in heat that characterizes gorillas and chimpanzees was absent in Ardipithecus.

That implies, Lovejoy concluded, that the males were beginning to enter into monogamous relationships with females and devoted a greater proportion of their time to caring for their young than did earlier ancestors."This is a restatement of Owen Lovejoy's ideas going back almost three decades, which I found unpersuasive then and still do," Pilbeam said. Hill was more blunt, calling Lovejoy's speculation "patent nonsense."

thomas.maugh@latimes.com
Copyright © 2009, The Los Angeles Times
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Around the Web
Treasure trove of fossils may turn ’evolution on its head’chicagotribune.com
Our long-lost motherguardian.co.uk
Fossils find in Ethiopia threatens to ’turn evolution on its head’baltimoresun.com

A second version of this stunning Knewz from the U.K. Guardian online press~

http://www.guardian.co.uk/science/2009/oct/01/fossil-ardi-human-race


How fossil Ardi pushes back the story of human evolution farther than ever before

Fossil Ardi reveals the first steps of the human race
Ardi evolved from the common ancestor we share with chimpanzees and was equally at home walking on the ground and swinging through the trees

Ian Sample, science correspondent
guardian.co.uk, Thursday 1 October 2009 15.30 BST

Link to this video
The remains of a woman who lived and died at the dawn of humanity have been uncovered in Ethiopia, giving the clearest picture yet of the origin of our species.

The partial skeleton, the oldest from a human ancestor ever ­discovered, belonged to a female who walked on two legs but was adept at climbing trees and moving through the forest canopy some 4.4m years ago.

Experts have described the find as the most important regarding human evolution in the past century.

The woman, named Ardi by the researchers who worked on her, belongs to a new species Ardipithecus ramidus and may be the earliest human ancestor ever discovered that was capable of walking upright.

The finding sheds light on a critical but unknown period of evolution at the root of the human family tree, shortly after our ancestors split from chimpanzees more than 6m years ago.
Remnants of the skeleton, skull, pelvis, hands, feet and other bones were excavated from the reddish-brown sediments of an ancient river system near the village of Aramis in northern Ethiopia, along with fragments from at least 35 other individuals.

Fossil hunters first glimpsed the new species in 1992 when a tooth belonging to Ardipithecus was spotted among pebbles in the desert near Aramis. Over the next two years, the researchers scoured the area on hands and knees and slowly uncovered pieces of bone from the hand, ankle and lower jaw, and finally a crushed skull.

A total of 47 researchers then spent a further 15 years removing, preparing and studying each of the fragments ahead of the publication tomorrow of an in-depth description of the species in 11 papers in the US journal Science.

Their investigation shows Ardi stood four feet (1.2m) tall and weighed a little under eight stone (50kg), making her similar in size and weight to a living chimpanzee. But many of Ardi's features are far more primitive than those seen in modern apes, suggesting chimpanzees and gorillas have evolved considerably after they split from the common ancestor they shared with humans.
The discovery of Ardi provides vital clues about the earliest human ancestor that lived at the fork in the evolutionary road that led to humans on one side and chimps on the other.


Link to this audio

"Darwin was very wise on this matter. 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," said Tim White, a lead author on the study and professor of human evolution at the University of California, Berkeley. "Well, we haven't found it, but we've come closer than we've ever come, at 4.4 million years ago."

The remains of animals, seeds and pollen uncovered at the excavation site reveal it to have been a woodland where colobus monkeys swung in trees full of swifts, doves and lovebirds, and spiral-horned antelope, elephants, shrews and early forms of peacock roamed the forest floor below.
The discovery is being seen as more important than Lucy, the 3.2m-year-old skeleton of a potential human ancestor which proved at a stroke that early humans walked upright before evolving large brains. The remains of Lucy, who belongs to the species Australopithecus afarensis, were uncovered in another part of Ethiopia in 1974.

"We thought Lucy was the find of the century but, in retrospect, it isn't," palaeontologist Andrew Hill at Yale University told Science. "It's worth the wait."

Measurements of Ardi's skeleton reveal she had a brain the size of a chimp's, but very long arms and fingers, and opposable toes that would have helped her grasp branches while moving through the forest.

Though Ardi would have spent much of her time in the trees, her pelvis was adapted to walking upright when she came down to the forest floor. Her unusual skeleton led White to comment of her species that "if you wanted to find something that moved like these things, you'd have to go to the bar in Star Wars."

Analysis of Ardi's teeth points to a diet of figs and other fruit, leaves and small mammals. Remarkably, both male and female Ardipithecus had very small incisors and canines, which are enlarged in modern apes. The finding suggests that unlike chimpanzees, baboons and gorillas, the male did not bare its teeth in battles over females and was already part of a more cooperative social group. It was probably involved in the parenting process.

"Natural selection has led to the reduction of this male canine tooth very, very early in time, right at the base of our branch of the family tree."

It may take years to confirm exactly where Ardi fits in the history of human evolution. One possibility is that she is a direct ancestor of Lucy's species, Australopithecus.

"The most important thing in the broader sense is that we now no longer have to guess about where we came from ... We now have an evidentiary basis for understanding that we didn't get here in the form we see today, we evolved," said White.

Chris Stringer, head of human origins at the Natural History Museum in London, said: "This is as important as the Lucy skeleton in terms of what it tells us about an even earlier stage of human evolution."

"The assumption among many researchers is that while humans have evolved a lot, chimps haven't changed much, so we can use them as a model of the common ancestor we shared. But why shouldn't chimps have changed? Everything evolves."

"We are really trying to establish what set us off on our evolutionary path," he added. "What would start the process off? That is one of the great mysteries."

In pictures: Standing tall
Gallery (9 pictures): The remains of a woman who lived at the dawn of humanity give the clearest picture yet of the origin of our species

Ardi's link to chimpanzees
Audio (10min 14sec): Anthropologist Tim White explains how fossil Ardi relates to the last common ancestor we share with chimpanzees
The discovery
Audio (9min 36sec): How the earliest human ancestor ever found came to light in Ethiopia
How she lived
Audio (11min 40sec): Ardi's probable lifestyle: how she moved, what she ate, social relations
The male of the species
Audio (12min 59sec): What the small teeth of male Ardipithecus tells us about their socialisation
Related
1 Oct 2009
Audio: Fossil Ardi Tim White on the male of the species
1 Oct 2009
Audio: Fossil Ardi Tim White on how Ardi lived
1 Oct 2009
Audio: Fossil Ardi Tim White on the link to chimpanzees
21 Sep 2009
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Fossil Ardi illuminates the dawn of humanityThis article was first published on guardian.co.uk at 15.30 BST on Thursday 1 October 2009. It was last updated at 18.55 BST on Thursday 1 October 2009.
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Fossil Ardi reveals the first steps of the human race