Ancestors of Modern Day Humans Came Down From the Trees to Become Bipedal

In the Aug. 10th 2009 issue of the journal Proceedings of the National Academy of Sciences, researchers have postulated that "early humans walked on their knuckles before evolving the ability to walk upright, but a new study suggests they may have bypassed that step"

Researchers have developed their ideas from their detailed examination of "the wrist bones of several primate species, and found that humans more likely evolved from a tree-climbing ancestor, rather than a knuckle-walking one. The new model reignites a longstanding debate about the origin of walking on two legs, or bipedalism, in humans."

Scientists believe that: "Since humans' closest living relatives, the African apes, often move around on knuckles and legs, many experts thought human ancestors may have also employed knuckle-walking. But another camp of scientists traces humans' two-legged walking to earlier tree-climbing, a mode of locomotion that is used by all living apes."

Analysis provided by "evolutionary anthropologist Tracy Kivell of Duke University compared juvenile and adult wrist bones of chimps and bonobos, our closest living primate kin, with those of gorillas."

Dr. Kivell "found two key bone features associated with knuckle-walking in 96 percent of adult chimpanzees and 76 percent of bonobos, but in only 6 percent of the gorilla specimens she studied."

Researchers have 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, while chimps and bonobos walk more flexibly with their wrists bent."

"We sat down together and asked, 'What are the differences between them?'" said co-researcher Daniel Schmitt. "The answer," Schmitt explained, is "that chimps and bonobos spend a lot of time in the trees. And gorillas do not."

Researchers "Kivell and Schmitt think this suggests that knuckle walking evolved independently in the two African ape lineages. The researchers also think that some features of the hand and wrist found in the human fossil record that have traditionally been treated as indicators of knuckle-walking behavior are more likely to be related to tree climbing."

The evidence suggests that the ancestors of humans climbed in trees, and then eventually moved to the ground and began walking upright, the researchers said."

"We have the most robust data I've ever seen on this topic," Schmitt said. "This model should cause everyone to re-evaluate what they've said before."

"There are no fossils from the time of this transition, which likely occurred about seven million years ago, Kivell and Schmitt said."

Missing Link: A Transitional Species Between Ancient Mammals and Primates Thought to be Found in Fossil of "Ida"

The beautifully preserved remains of a 47-million-year-old, lemur-like creature have been unveiled in the US.

"Scientists have unveiled a 47-million-year-old fossilised skeleton of a monkey hailed as the missing link in human evolution.

"The search for a direct connection between humans and the rest of the animal kingdom has taken 200 years - but it was presented to the world today at a special news conference in New York.

"The discovery of the 95%-complete 'lemur monkey' - dubbed Ida - is described by experts as the "eighth wonder of the world"

"The preservation is so good, it is possible to see the outline of its fur and even traces of its last meal.



"The fossil, nicknamed Ida, is claimed to be a "missing link" between today's higher primates - monkeys, apes and humans - and more distant relatives.

"But some independent experts, awaiting an opportunity to see the new fossil, are sceptical of the claim.

"And they have been critical of the hype surrounding the presentation of Ida.

"The fossil was launched amid great fanfare at the American Museum of Natural History in New York, by the city's mayor.

"Although details of the fossil have only just been published in a scientific journal - PLoS One - there is already a TV documentary and book tie-in.

"She belongs to the group from which higher primates and human beings developed but my impression is she is not on the direct line." Dr Jens Franzen conjectured.

"Ida was discovered in the 1980s in a fossil treasure-trove called Messel Pit, near Darmstadt in Germany. For much of the intervening period, it has been in a private collection.

"The investigation of the fossil's significance was led by Jorn Hurum of the Natural History Museum in Oslo, Norway.



"He said the fossil creature was "the closest thing we can get to a direct ancestor" and described the discovery as "a dream come true".

"The female animal lived during an epoch in Earth history known as the Eocene, which was crucial for the development of early primates - and at first glance, Ida resembles a lemur.

"But the creature lacks primitive features such as a so-called "toothcomb", a specialised feature in which the lower incisor and canine teeth are elongated, crowded together and projecting forward. She also lacks a special claw used for grooming.

"The team concluded that she was not simply another lemur, but a new species. They have called her Darwinius masillae, to celebrate her place of origin and the bicentenary of the birth of Charles Darwin.

"Dr Jens Franzen, an expert on the Messel Pit and a member of the team, described Ida as "like the Eighth Wonder of the World", because of the extraordinary completeness of the skeleton.

"It was information "palaeontologists can normally only dream of", he said.

"In addition, Ida bears "a close resemblance to ourselves" he said, with nails instead of claws, a grasping hand and an opposable thumb - like humans and some other primates. But he said some aspects of the teeth indicate she is not a direct ancestor - more of an "aunt" than a "grandmother".

"She belongs to the group from which higher primates and human beings developed but my impression is she is not on the direct line."

Independent experts are keen to see the new fossil but somewhat sceptical of any claim that it could be "a missing link".

Dr Henry Gee, a senior editor at the journal Nature, said the term itself was misleading and that the scientific community would need to evaluate its significance.

"It's extremely nice to have a new find and it will be well-studied," he said. But he added that it was not likely to be in the same league as major discoveries such as "Flores man" or feathered dinosaurs.

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"Dr Chris Beard, curator of the Carnegie Museum of Natural History and author of The Hunt for the Dawn Monkey, said he was "awestruck" by the publicity machine surrounding the new fossil.

"He argued that it could damage the popularisation of science if the creature was not all that it was hyped up to be.

"Dr Beard has not yet seen scientific details of the find but said that it would be very nice to have a beautiful new fossil from the Eocene and that Ida would be "a welcome new addition" to the world of early primates.

"But he added: "I would be absolutely dumbfounded if it turns out to be a potential ancestor to humans."

"In the PLoS paper itself, the scientists do not actually claim the specimen represents a direct ancestor to us. But Dr Hurum believes that is exactly what Ida is.

"He told BBC News that the key to proving this lay in the detail of the foot. The shape of a bone in the foot called the talus looks "almost anthropoid".

"He said the team was now planning a 3D reconstruction of the foot which would prove this.

"We're not finished with this specimen yet," said Dr Hurum. "There will be plenty more papers coming out."