Fossil remains of a short human-like creature that lived 4.4 million years ago could be the closest thing yet to the mythical “missing link”, it was revealed today.
The almost intact female “hominid” skeleton, unearthed from a desert in Ethiopia, is the oldest known and writes a new chapter in human evolution.
Ardipithecus ramidus, nicknamed "Ardi" by scientists, possessed an amalgam of human and ape or monkey traits. Experts believe she stood about four feet tall and walked on two legs on the ground some of the time, while also living in trees.
However scientists were surprised to discover that her anatomy was very different from that of present-day chimpanzees.
Ardi lacked the acrobatic ability of the modern-day apes and did not swing or hang from branches. Instead she would have climbed carefully on all fours, grasping with her long hands and feet.
Her face was more vertical and human-like than a chimp’s, having a jaw that jutted out less and was not armed with sharp, dagger-like canine teeth. She is believed to have been omnivorous, eating berries, fruits and roots as well as small mammals.
Ardi is also thought to have had a back that was long and curved like a human’s rather than short and stiff like a chimpanzee’s. Yet her lower pelvis was large and primitive, sharing similarities with African apes.
Humans and chimpanzees are believed to share an as-yet undiscovered common ancestor which lived between about five and seven million years ago.
Previously it had been assumed that very ancient hominids close to the point where the two struck out on different evolutionary paths would closely resemble chimps.
Ardi’s unusual bones suggest this was not the case. Scientists now believe modern chimpanzees have been extensively shaped by evolution, and should not be viewed as “proxies” for the last common ancestor of African apes and humans.
Despite having some strongly human characteristics, Ardi was still a lot less human than the famous “Lucy” - another primitive hominid from Africa that lived a million years later.
Lucy's partial skeleton, found in Ethiopia in 1974, was the oldest comprehensive set of hominid remains known before Ardi's discovery. Her species, Australopithecus afarensis, was an adept biped that seemed to be fully committed to life on the ground.
Professor Tim White, from the University of California at Berkeley, one of the leading authors who described Ardi today in a special issue of the journal Science, said: "In Ardipithecuswe have an unspecialised 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."
He added that Charles Darwin was “very wise” on the subject of human origins, warning of the dangers of making rash assumptions about our heritage.
“Darwin said we have to be really careful,” said Dr White. “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. 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.”
Piecing together and analysing the skeleton took 17 years of painstaking work.
Older individual hominid fossils have been found, including a skull from Chad dating back more than six million years, and a number of other teeth and bone fragments. But Ardi is easily the most ancient complete set of skeletal bones to be unearthed so far.
A film on the find, Discovering Ardi, has been made for Discovery Channel.