Fossils Reveal New Branch of Humans’ Family Tree
Fossils of a previously unknown pre-human species have been discovered in Ethiopia, along with the earliest known evidence that such primitive creatures used stone tools to butcher the animals on which they feasted, an international research team announced Thursday.
Working in the arid washes of the Afar Desert, a team of 40 researchers from 13 countries unearthed bones, teeth and skull fragments representing a new branch of the human family tree that displays a remarkable combination of primitive and advanced features.
Indeed, the new species is so unlike anything scientists expected to find at that juncture of early human evolution that part of its formal scientific name--Australopithecus garhi--means “surprise” in the local language of the Afar.
The discoveries--detailed in research published today in Science--offer the first detailed look at life on the ancient grasslands and lake shores of East Africa at a crucial crossroads in human development 2.5 million years ago. It was a time when several pre-human species vied for survival and only one emerged as the direct ancestor of the genus from which modern humanity sprang.
The new species may represent the best candidate yet for the direct ancestor of the genus Homo, to which modern humanity belongs, said Ethiopian anthropologist Berhane Asfaw and UC Berkeley fossil hunter Tim D. White, who together led the research team.
Only yards away from Asfaw and White’s dig, scientists led by UC Berkeley’s J. Desmond Clarke also found clear signs that such pre-human creatures used stone tools to butcher antelope and smash the rich marrow from their bones. This buttresses a theory that the eating of meat was a critical spur to human evolution.
Taken together, the new finds offer provocative evidence that changes in behavior, such as a turn to meat eating, preceded anatomical changes, including the development of the large brain that is humankind’s most singular feature.
They also leave the roots of the human family tree more tangled than ever, with as many as eight different pre-human Australopithecus species now identified from the fossil record. There is no conclusive evidence of just how they are all related.
“With the addition of this to the inventory, there are more species than one can shake a stick at,” said anthropologist Philip Rightmire at the State University of New York in Binghamton. “Now it will be a real challenge to sort them out and put them into a coherent evolutionary scheme.”
In the contentious field of human origins, there may be no more major event than the discovery of a new ancestral species. Such announcements are as much an occasion for fierce scholarly debate as for celebration. But the newest find appeared to be winning almost instant acceptance as a distinct species.
“It is out of kilter from anything else we have known, so it has to be another species,” said anthropologist F. Clark Howell at UC Berkeley, who called the discovery “fantastic.” He added, “It is very important because we have not had anything of any substance from around this time.”
Andrew Hill, curator of anthropology at Yale University’s Peabody Museum, agreed. “It is very important . . . very intriguing.”
Rightmire said, “They have made a convincing case for naming the new species.”
University of Arizona anthropologist Donald C. Johanson, who discovered the predecessor species from whom the new pre-humans most likely evolved, said, “It is a very welcome discovery. [The new species] was not only anatomically different but behaviorally different. It is tantalizing material.
“The whole human family tree is more complex than we have thought before,” Johanson said.
Although the researchers hope their new species will turn out to be the long-sought immediate ancestor of human beings, they stopped short of formally claiming that most coveted status for their fossil find--at least for the moment.
“It is in the right place, at the right time, to be the ancestor of early Homo, however defined,” the team reported. “Nothing about its morphology would preclude it from occupying this position.”
Even so, they will have to cull many more fossils from the Ethiopian gravel before they can be sure the new species was not just an evolutionary dead end.
“There is a definite diversity to the human family tree and it is not clear which way it went,” said Hill at Yale. “This is clearly different from other things. It is plausible, at least, that it leads to the [human] line. But like all these discoveries, it raises a lot of new questions.”
Representing the partial remains of several individuals, the fossils add up to a composite picture of a creature that is at once apelike and surprisingly human.
“A lot of people will be surprised by this combination of features,” White said.
In life, the hominid creature stood about 4 feet, 10 inches tall.
It had protruding facial features, not unlike a chimpanzee. Its jaw was lined with molars three times the size of those in modern human beings and canine teeth almost as large, while its brain was barely one-third human size.
Its legs were long and human-like. Its arms were long and more like an ape’s. And, if the smashed, scraped and splintered bones found at the site were in fact the work of its hands, it was also an accomplished scavenger who used stone knives to filet meat and who grew fat on meals of marrow.
“It is a monstrous thing,” said Howell, musing on its unusual appearance.
Bones of antelopes, horses and other large mammals found only a yard away from the hominid remains show cut marks from tools, in the first known instance of human tool use to butcher animals. It is important evidence that meat had become a major part of the pre-human diet much earlier than many researchers had surmised.
An examination of the scratches and gouges on the bones shows that stone tools were used to cut away flesh and tendons. Hammer stones were used to break the bones at both ends.
So far, the researchers have not found the tools themselves. Nor can they be positive that members of the new species were the ones who used them.
The world’s oldest known tools, which also date to 2.5 million years ago, were discovered in 1997 just 60 miles away at a site called Gona. Until now no one had any idea what species might have made them.
Several anthropologists have speculated that just such a switch to a high-energy, high-fat meat diet led to an increase in brain size that took place within a few hundred thousand years.
“It is a dietary revolution,” said White. “It is really a key element in the human career.”
