Sunday, 25 October 2009

The feet of Homo floresiensis were primitive but not pathological

A detailed analysis of the feet of Homo floresiensis—the miniature hominins who lived on a remote island in eastern Indonesia until 18,000 years ago—may help settle a question hotly debated among paleontologists: how similar was this population to modern humans? A new research paper, featured on the cover of the current issue of Nature, may answer this question. While the so-called "hobbits" walked on two legs, several features of their feet were so primitive that their gait was not efficient.

"The hobbits were bipedal, but they walked in a different way from modern humans," explains William Harcourt-Smith, a Research Scientist in the Division of Paleontology at the American Museum of Natural History and an author on the paper. "Their feet have a combination of human-like and more primitive early hominin traits, some of which are more akin to those in Lucy." Lucy is an early bipedal but small-brained hominin, or australopithecine, that lived in Africa 3.2 million years ago.

The "hobbits," excavated from Liang Bua Cave on the island of Flores, were first described in 2004. Known specimens range in age from 90,000 to 18,000 years old, making them contemporaneous with modern humans. This, in combination with the unusually small stature and brain size of H. floresiensis, led to considerable debate among researchers and in the press. Some consider the population a separate species, while others have assessed the fossils as pathological modern humans. But a number of recent analyses of the skull, face, and wrist have found many unusually primitive features among the "hobbits" that are more similar to chimpanzees and Australopithecus, suggesting that the Flores inhabitants represent a remnant population of early hominins.

The anatomy of the foot described in the new paper might finally answer the pathological modern vs. primitive population question. Although the foot is characteristic of a biped—being stiff and having no opposable big toe—many other traits fall outside of the range for modern humans. The H. floresiensis foot is very long in proportion to the lower limb and considerably more than half the length of the thighbone; modern human feet are relatively shorter at about half of the femur's length. The stubby big toe of the hobbits is another primitive, chimp-like trait. But the pivotal clue comes from the navicular bone, an important tarsal bone that helps form the arch in a modern human foot. The "hobbit" navicular bone is more akin to that found in great apes, which means that these hominins lacked an arch and were not efficient long-term runners.
"Arches are the hallmark of a modern human foot," explains Harcourt-Smith. "This is another strong piece of the evidence that the "hobbit" was not like us."

Researchers also assessed the pathology hypothesis by comparing "hobbit" feet to those of typical modern humans and pathological modern specimens such as pituitary dwarfs. While the pathological specimens fell well within the range of modern humans, the "hobbits" did not. This suggests that H. floresiensis was an unusual, isolated population of early hominins.

"The fossil record continues to surprise us," says William Jungers, Chairman of the Department of Anatomical Sciences at Stony Brook University Medical Center, and an author on the study. "H. floresiensis is either an island-dwarfed descendant of H. erectus that not only underwent body-size reduction but also extensive evolutionary reversals, or, as our analysis suggests, it represents a new species full of primitive retentions from an ancestor that dispersed out of Africa much earlier than anyone would have predicted. Either way, the implications for human evolution are profound."

Source:Eurekalert 09.

Friday, 23 October 2009

Charles Darwin: In His Footsteps

3 October 2009-30 August 2010
Free entry

See Charles Darwin's story unfold through larger than life illustrations in a graphic novel style alongside fantastic objects, some collected by Darwin himself.
See Darwin as you have never seen him before and discover the key moments in the development of his career, from his childhood interest in nature to his discovery of the most important idea in biology. Find out about the importance of Darwin's less well known work, from pigeon breeding to the origin of coral reefs on submarine volcanoes.
Explore the reaction to Darwin's ideas and their impact on science and society.
Discover how natural selection continues to create the diversity we see in the natural world- just what is a species and what is the evidence for evolution?
Find out about Manchester's links to Darwin's ideas - from the story of the Peppered Moth to the history of The Manchester Museum.

Experience extraordinary places and wildlife through the evocative words of Charles Darwin and breathtaking images from photographer Ben Hall.
"The glories of the vegetation of the Tropics rise before my mind at the present time more vividly than anything else. Though the sense of sublimity, which the great deserts of Patagonia and the forest-clad mountains of Tierra del Fuego excited in me, has left an indelible impression on my mind." (From Charles Darwin's autobiography, written in 1876, 40 years after the voyage of the Beagle)
"In many parts magnificent glaciers extended from the mountain side to the water's edge. It is scarcely possible to imagine any thing more beautiful than the beryl-like blue of the glacier, and especially when contrasted with the dead white of an expanse of snow. As fragments fell from the glacier into the water, they floated away, and the channel with its icebergs represented in miniature the polar sea." (The Voyage of the Beagle, p.245, January 1833 Tierra del Fuego)
Charles Darwin spent more time in South America than he did anywhere else when voyaging on HMS Beagle during 1831-36. Darwin's popular account of his experiences, usually called The Voyage of the Beagle, was published in 1845 and became an instant bestseller. This book has been one of the most popular travel narratives ever written. The book contains many evocative descriptions of the things Darwin saw.
Ben Hall is one of Britain's foremost wildlife photographers. His personal approach to wildlife photography lies in the creative art of 'seeing'. His aim is to use his pictures to communicate his personal vision, to generate an emotional response and to excite the viewer's aesthetic sensitivity. Ben often pre-visualises a particular image in his mind before setting out to photograph it. To realise this vision by turning it into a photographic image can take weeks or even months, and often sees him returning frequently to the same location to capture the perfect shot.
Find out more about Ben Hall at:
Read about Charles Darwin's time in South America here:
Read Charles Darwin's letters here:
Dinosaur evolution
Evolution of birds
Evolution of microbes
Molecular evolution

Bipedal Humans Came Down From The Trees, Not Up From The Ground

A detailed examination of the wrist bones of several primate species challenges the notion that humans evolved their two-legged upright walking style from a knuckle-walking ancestor.

The same lines of evidence also suggest that knuckle-walking evolved at least two different times, making gorillas distinct from chimpanzees and bonobos.
"We have the most robust data I've ever seen on this topic," said Daniel Schmitt, a Duke University associate professor of evolutionary anthropology. "This model should cause everyone to re-evaluate what they've said before."
A report on the findings will appear online during the week of Aug. 10 in the research journal Proceedings of the National Academy of Sciences.
The research, led by post-doctoral research associate Tracy Kivell, was supported by the Natural Sciences and Engineering Research Council in her native Canada, General Motors' Women in Science and Mathematics, and the University of Toronto, where Kivell did her Ph.D. work.
The debate over the origins of human bipedalism began during Charles Darwin's lifetime and continues vigorously to this day, commonly dividing into two competing models, the researchers explained.
One model "envisions the pre-human ancestor as a terrestrial knuckle-walker, a behavior frequently used by our closest living relatives, the African apes," they wrote in the PNAS report. The other model traces our two-legged walking to earlier tree-climbing, a mode of locomotion that is used by all living apes.
Supporters of the knuckle-walking origin think we and African apes evolved from a common knuckle walking ancestor. That connection, they contend, is still evident in wrist and hand bone features shared by African apes and by fossil and living humans.
But Kivell found otherwise when she began comparing juvenile and adult wrist bones of more than 100 chimps and bonobos, our closest living primate kin, with those of gorillas.
Significantly, two key features associated with knuckle walking were present in only 6 percent of the gorilla specimens she studied. But she found them in 96 percent of adult chimpanzees and 76 percent of bonobos. In all, she looked at specimens from 91 gorillas, 104 chimps and 43 bonobos.
Kivell and Schmitt suggested that one explanation for the absence of these features in gorillas is that they knuckle-walk in a fundamentally different way from chimps and bonobos. Gorillas stride with their arms and wrists extended straight down and locked in what Kivell called "columnar" stances that resemble how elephants walk. By contrast, chimps and bonobos walk more flexibly, "with their wrists in a bent position as opposed to being stacked-up," she said. "And with their wrists in bent positions there will be more stresses at those joints."
As a result, chimp and bonobo wrists have special features that gorillas lack -- little ridges and concavities that serve as "bony stops" to keep their wrists from over-bending. Gorillas don't need those, she added.
"When we first got together to work on this study that (difference) really jumped out in living color," Schmitt said.
"Then we sat down together and asked: 'What are the differences between them?' Schmitt said. "The answer is that chimps and bonobos spend a lot of time in the trees. And gorillas do not."
Chimpanzees and bonobos have a more extended-wrist way of knuckle-walking which gives them added stability on branches, the researchers concluded. In contrast, gorillas' "columnar" style of knuckle-walking is consistent with ground transport.
Indeed, "from what we know about knuckle-walking among wild populations, gorillas and adult chimpanzees will both knuckle-walk about 85 percent of the time that they're moving," Kivell said. "But chimpanzees and bonobos are more arboreal than gorillas. So they're doing a lot more of it in the trees."
Kivell and Schmitt think this suggests independent evolution of knuckle-walking behavior in the two African ape lineages.
Some scientists point to features in the human anatomy as our own vestiges of a knuckle-walking ancestry. One notable example is the fusion a two wrist bones that could provide us extra stability, a feature we share with gorillas, chimps and bonobos.
But some lemurs have that feature too, and they do a variety of different movements in the trees but do not knuckle-walk, Kivell said.
Altogether, the evidence leans against the idea that our own bipedalism evolved from a knuckle-walking ancestor, the pair wrote. "Instead, our data support the opposite notion, that features of the hand and wrist found in the human fossil record that have traditionally been treated as indicators of knuckle-walking behavior in general are in fact evidence of arboreality."
In other words, a long-ago ancestor species that spent its time in the trees moved to the ground and began walking upright.
There are no fossils from the time of this transition, which likely occurred about seven million years ago, Kivell and Schmitt said. But none of the later fossils considered to be on the direct human line were knuckle-walkers.

Source:Eurekalert 2009/10

Wednesday, 21 October 2009

"Ida" 47 million year old primate.

The article, entitled, Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology, documents the discovery of a remarkably complete and well-preserved fossil of an extinct early primate in Messel Pit, Germany, a site of great significance for fossils of the Eocene epoch.

The creature, named Darwinius masillae by the paper’s authors, lived an estimated 47 million years ago and is the first example of a previously unknown genus of primate. The fossil, known as “Ida,” is 95% complete and includes the skeleton, an outline of the creature’s body and the contents of her gut, allowing the researchers to reconstruct her life history and diet. Ida was an agile, young, herbivorous, female, about the size of a small monkey, who feasted on fruit and leaves in the trees of the Messel rain forest and died, aged about nine months, at the edge of a volcanic lake.

Although Darwinius masillae shares some characteristics with prosimians, such as the lemur, X-rays of the fossil crucially reveal the lack of a “toothcomb” and a “grooming claw,” an attribute of lemurs. Meanwhile, the fossil’s opposable big toes and nail-bearing fingers and toes confirm it to be a primate, and a foot bone called the talus bone links Ida directly to humans. Ida thus provides the most complete understanding of the paleobiology of any Eocene primate so far discovered.

“This fossil is so complete,” said Dr Hurum. “Everything’s there. It’s unheard of in the primate record at all. You have to get to human burial to see something that’s this complete.”

Thursday, 15 October 2009

Ardi's feet, pelvis, legs, and hands suggest she was a biped on the ground but a quadruped when moving about in the trees

Picture courtesy J. H. Matternes via Science/AAAS
Scientists today announced the discovery of the oldest fossil skeleton of a human ancestor. The find reveals that our forebears underwent a previously unknown stage of evolution more than a million years before Lucy, the iconic early human ancestor specimen that walked the Earth 3.2 million years ago.
The centerpiece of a treasure trove of new fossils, the skeleton—assigned to a species called Ardipithecus ramidus—belonged to a small-brained, 110-pound (50-kilogram) female nicknamed "Ardi." (See pictures of Ardipithecus ramidus.)
The fossil puts to rest the notion, popular since Darwin's time, that a chimpanzee-like missing link—resembling something between humans and today's apes—would eventually be found at the root of the human family tree. Indeed, the new evidence suggests that the study of chimpanzee anatomy and behavior—long used to infer the nature of the earliest human ancestors—is largely irrelevant to understanding our beginnings.
(Interactive time line: how the Ardipithecus ramidus discovery changes human evolutionary theory.)
Ardi instead shows an unexpected mix of advanced characteristics and of primitive traits seen in much older apes that were unlike chimps or gorillas (interactive: Ardi's key features). As such, the skeleton offers a window on what the last common ancestor of humans and living apes might have been like.
The analysis of the Ardipithecus ramidus bones will be published in a collection of papers tomorrow in a special edition of the journal Science, along with an avalanche of supporting materials published online.
"This find is far more important than Lucy," said Alan Walker, a paleontologist from Pennsylvania State University who was not part of the research. "It shows that the last common ancestor with chimps didn't look like a chimp, or a human, or some funny thing in between."

Ardi Surrounded by Family
The Ardipithecus ramidus fossils were discovered in Ethiopia's harsh Afar desert at a site called Aramis in the Middle Awash region, just 46 miles (74 kilometers) from where Lucy's species, Australopithecus afarensis, was found in 1974. Radiometric dating of two layers of volcanic ash that tightly sandwiched the fossil deposits revealed that Ardi lived 4.4 million years ago.
Older hominid fossils have been uncovered, including a skull from Chad  at least six million years old and some more fragmentary, slightly younger remains from Kenya and nearby in the Middle Awash.
While important, however, none of those earlier fossils are nearly as revealing as the newly announced remains, which in addition to Ardi's partial skeleton include bones representing at least 36 other individuals.
"All of a sudden you've got fingers and toes and arms and legs and heads and teeth," said Tim White of the University of California, Berkeley, who co-directed the work with Berhane Asfaw, a paleoanthropologist and former director of the National Museum of Ethiopia, and Giday WoldeGabriel, a geologist at Los Alamos National Laboratory in New Mexico.
"That allows you to do something you can't do with isolated specimens," White said. "It allows you to do biology."

Ardi's Weird Way of Moving
The biggest surprise about Ardipithecus's biology is its bizarre means of moving about.
All previously known hominids—members of our ancestral lineage—walked upright on two legs, like us. But Ardi's feet, pelvis, legs, and hands suggest she was a biped on the ground but a quadruped when moving about in the trees.
Her big toe, for instance, splays out from her foot like an ape's, the better to grasp tree limbs. Unlike a chimpanzee foot, however, Ardipithecus's contains a special small bone inside a tendon, passed down from more primitive ancestors, that keeps the divergent toe more rigid. Combined with modifications to the other toes, the bone would have helped Ardi walk bipedally on the ground, though less efficiently than later hominids like Lucy. The bone was lost in the lineages of chimps and gorillas.
According to the researchers, the pelvis shows a similar mosaic of traits. The large flaring bones of the upper pelvis were positioned so that Ardi could walk on two legs without lurching from side to side like a chimp. But the lower pelvis was built like an ape's, to accommodate huge hind limb muscles used in climbing.
Even in the trees, Ardi was nothing like a modern ape, the researchers say.
Modern chimps and gorillas have evolved limb anatomy specialized to climbing vertically up tree trunks, hanging and swinging from branches, and knuckle-walking on the ground.
While these behaviors require very rigid wrist bones, for instance, the wrists and finger joints of Ardipithecus were highly flexible. As a result Ardi would have walked on her palms as she moved about in the trees—more like some primitive fossil apes than like chimps and gorillas.
"What Ardi tells us is there was this vast intermediate stage in our evolution that nobody knew about," said Owen Lovejoy, an anatomist at Kent State University in Ohio, who analyzed Ardi's bones below the neck. "It changes everything."
Against All Odds, Ardi Emerges
The first, fragmentary specimens of Ardipithecus were found at Aramis in 1992 and published in 1994. The skeleton announced today was discovered that same year and excavated with the bones of the other individuals over the next three field seasons. But it took 15 years before the research team could fully analyze and publish the skeleton, because the fossils were in such bad shape.
After Ardi died, her remains apparently were trampled down into mud by hippos and other passing herbivores. Millions of years later, erosion brought the badly crushed and distorted bones back to the surface.
They were so fragile they would turn to dust at a touch. To save the precious fragments, White and colleagues removed the fossils along with their surrounding rock. Then, in a lab in Addis, the researchers carefully tweaked out the bones from the rocky matrix using a needle under a microscope, proceeding "millimeter by submillimeter," as the team puts it in Science. This process alone took several years.
Pieces of the crushed skull were then CT-scanned and digitally fit back together by Gen Suwa, a paleoanthropologist at the University of Tokyo.
In the end, the research team recovered more than 125 pieces of the skeleton, including much of the feet and virtually all of the hands—an extreme rarity among hominid fossils of any age, let alone one so very ancient.
"Finding this skeleton was more than luck," said White. "It was against all odds."
Ardi's World
The team also found some 6,000 animal fossils and other specimens that offer a picture of the world Ardi inhabited: a moist woodland very different from the region's current, parched landscape. In addition to antelope and monkey species associated with forests, the deposits contained forest-dwelling birds and seeds from fig and palm trees.
Wear patterns and isotopes in the hominid teeth suggest a diet that included fruits, nuts, and other forest foods.
If White and his team are right that Ardi walked upright as well as climbed trees, the environmental evidence would seem to strike the death knell for the "savanna hypothesis"—a long-standing notion that our ancestors first stood up in response to their move onto an open grassland environment.
Sex for Food
Some researchers, however, are unconvinced that Ardipithecus was quite so versatile.
"This is a fascinating skeleton, but based on what they present, the evidence for bipedality is limited at best," said William Jungers, an anatomist at Stony Brook University in New York State.
"Divergent big toes are associated with grasping, and this has one of the most divergent big toes you can imagine," Jungers said. "Why would an animal fully adapted to support its weight on its forelimbs in the trees elect to walk bipedally on the ground?"
One provocative answer to that question—originally proposed by Lovejoy in the early 1980s and refined now in light of the Ardipithecus discoveries—attributes the origin of bipedality to another trademark of humankind: monogamous sex.
Virtually all apes and monkeys, especially males, have long upper canine teeth—formidable weapons in fights for mating opportunities.
But Ardipithecus appears to have already embarked on a uniquely human evolutionary path, with canines reduced in size and dramatically "feminized" to a stubby, diamond shape, according to the researchers. Males and female specimens are also close to each other in body size.
Lovejoy sees these changes as part of an epochal shift in social behavior: Instead of fighting for access to females, a male Ardipithecus would supply a "targeted female" and her offspring with gathered foods and gain her sexual loyalty in return.
To keep up his end of the deal, a male needed to have his hands free to carry home the food. Bipedalism may have been a poor way for Ardipithecus to get around, but through its contribution to the "sex for food" contract, it would have been an excellent way to bear more offspring. And in evolution, of course, more offspring is the name of the game (more: "Did Early Humans Start Walking for Sex?").
Two hundred thousand years after Ardipithecus, another species called Australopithecus anamensis appeared in the region. By most accounts, that species soon evolved into Australopithecus afarensis, with a slightly larger brain and a full commitment to a bipedal way of life. Then came early Homo, with its even bigger brain and budding tool use.
Did primitive Ardipithecus undergo some accelerated change in the 200,000 years between it and Australopithecus—and emerge as the ancestor of all later hominids? Or was Ardipithecus a relict species, carrying its quaint mosaic of primitive and advanced traits with it into extinction?
Study co-leader White sees nothing about the skeleton "that would exclude it from ancestral status." But he said more fossils would be needed to fully resolve the issue.
Stony Brook's Jungers added, "These finds are incredibly important, and given the state of preservation of the bones, what they did was nothing short of heroic.
But this is just the beginning of the story."

Source:National Geographic 15/10/09