'Ardi:' Was the 4.4 Million-Year-Old Fossil Really the Oldest Human Ancestor?

May 28, 2010 — -- When Ardipithecus ramidus -- "Ardi" for short -- was shown off last fall, she took the scientific world by storm. Scientists said the 4.4-million-year-old fossil was the oldest pre-human species ever found.

"What we found in Ethiopia at 4.4 million years ago is the closest we've ever come to that ancestor along our own line," Tim White of the University of California at Berkeley told ABC News at the time.

"This may be the most important specimen in the history of evolutionary biology," said C. Owen Lovejoy of Kent State University.

But now comes word from other scientists who say, in effect, not so fast.

Writing in today's edition of the journal Science -- which published the original reports on Ardi and later called it the "breakthrough of the year" -- Esteban Sarmiento, a private researcher in New Jersey, says, "Their analysis of shared-derived characters provides insufficient evidence of an ancestor-descendant relationship...."

Sarmiento writes that Ardi probably came before humans and apes split into separate evolutionary family trees.

In a second paper, Thure Cerling of the University of Utah, along with several colleagues, writes that when Ardi was alive, Ethiopia was probably grassy savannah with a few trees -- not the woodlands that White and his team said was key to explaining the way Ardi evolved.

White, who stands by his team's original conclusions, said he was not surprised by the new questions. Part of the regular give-and-take of scientific work is for researchers to publish what they find -- specifically so that others can either confirm it or find contradictory evidence.

"Any time you publish something that challenges long-established views, the people who hold those long-established views are bound to push back," White said today in a conversation with ABC News.

"This is absolutely a normal part of science."

White and his colleagues said Ardipithecus is not the long-sought "missing link" -- the ancestor that scientists say humans and apes have in common -- but they said it comes close.