ardi fossil
A digitally rendered composite image from
Science shows the foot of the
partial skeleton.

Discovery of Oldest Hominid Fossil May End Search for Chimp-like Missing Link

October 02, 2009 05:28 PM
by Haley A. Lovett
“Ardi,” a 4.4 million-year-old early human fossil, may prove that a “missing link” between humans and chimps does not exist, and that both species evolved substantially from a common ancestor.

Ardi Suggests Humans May Not Have “Given Up” Chimp-like Traits

“Ardi,” named for the her species Ardipithecus ramidus, has some surprisingly un-chimp-like characteristics. Until now, many researchers had expected that an early human-like species would have knuckle walked like modern chimps, but according to ScienceNOW, Ardi’s pelvis indicates that she would have walked somewhat upright, and her toes indicate that she would have spent a time in the trees as well. Ardi also has much smaller canine teeth than modern apes, suggesting that her species was monogamous and didn’t need large teeth for fighting over mates.

What does this find mean? According to Ewen Callaway of New Scientist, it could mean that humans never evolved away from chimp-like traits such as knuckle walking, but rather that chimps developed those traits after the split from a common ancestor with humans 6 million years ago. This could also mean that the “missing link” species that some scientists thought would be found in the fossil record—sharing both traits common to modern humans and chimps—might never have existed.

National Geographic provides a timeline of human evolution, reflecting the changes brought about by the discovery of Ardi.

The Ardi fossil, along with fossils from 35 other individuals of the same species, was discovered, in Aramis, Ethiopia, nearly 15 years ago. According to Jamie Shreeve of National Geographic, it took such a long time for the results of the Ardi fossil to be published because the bones were trampled after Ardi’s death, and the fossils were so fragile upon being found that they would easily break apart when touched. Scientists used CT scans and microscopic excavation tools to isolate and examine the fossil.

Until now, the oldest known fossil of a human ancestor was “Lucy,” a bipedal species dated at 3.2 million years old. A much older specimen, dating about 47 million years old, and called “Ida,” was discovered in 1983 and thought to be a very ancient ancestor of some primate species (perhaps even humans). However scientists were cautious about the media frenzy calling Ida a “missing link,” noting that it was not a transitional species between apes and humans.

Discovery of Modern Human Fossils Heavily Debated

The 2003 discovery of an 18,000-year-old humanlike skull on an Indonesian island was at first thought to be a tiny human species, its size perhaps the result of the island environment or a congenital disorder. Later studies found that it is more likely that the species has an ancestor that is not common to Homo sapiens.

Related Topic: Scientist link modern chimp and human behavior

In the last few decades scientists have introduced new theories about the human-like behavior of chimps and other primates.

A recent study found that music could illicit emotional responses from monkeys, just as it can with humans. However the study found that the monkeys responded to music designed around the sounds that they make, and that music made for humans has little (or sometimes negative) effect on them.

Zookeepers in Sweden were surprised when they discovered that one of their chimps, Santino, had been “planning” attacks on zoo visitors by gathering stones in the morning, and then throwing them at visitors later in the day. This was a breakthrough discovery showing that chimpanzees had the ability to anticipate a future state of emotion.

Some baby apes have been found to laugh in much the same way that humans do—using controlled, deliberate breathing patterns to create sound—showing that laughter is actually a form of communication for species other than our own.

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