Scientists: 'Ardi' Fossil Sheds Light on Origin of Human Species

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Human's Oldest Relative Found

The story of humankind is reaching back another million years with the discovery of "Ardi," a hominid who lived 4.4 million years ago in what is now Ethiopia. (Oct. 1)

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The scientists found scores of other specimens, from both males and females, though the bones were for the most part scattered and isolated. Although Ardipithecus quickly entered the paleontology lexicon in the mid-1990s, and scientists knew that this was potentially a major discovery, it was not until Thursday -- and after some complaints by fellow scientists over how long the process was taking -- that White and his colleagues produced a detailed description of the species.

"Ardi tells us twice as much as Lucy did. We have hands and feet, a more complete environment, a more complete skeleton, it's older, it's more primitive, it shows us the process of transformation from common ancestor to hominid," said C. Owen Lovejoy, an anthropologist at Kent State University who was part of the Ardi team.

The origin of the human species via evolution from earlier primates is beyond scientific dispute. Even when the fossil record of Africa was virtually nonexistent, Charles Darwin argued that human beings probably evolved from African primates. Field work over the past century confirmed Darwin's hypothesis, which was bolstered further by laboratory analysis of the genetic codes of humans, chimpanzees and other primates. The fine details of human origin, however, has become sketchier, and more subject to interpretation and debate, as the researchers dig deeper into the past and the fossils become scarcer, more fragmentary and in many cases more enigmatic.

Scientists continue to search for the "Last Common Ancestor," sometimes abbreviated as the LCA. This is the creature to which both modern humans and modern chimpanzees can trace their ancestry. Many scientists believe the common ancestor lived about 7 million years ago. The new research on Ardi suggests that this ancestor didn't look nearly as much like a modern chimpanzee as had been previously suspected. Rather, the ancestor would have looked more like Ardipithecus. This suggests that chimpanzees, far from being time machines for visiting the distant past, have themselves evolved significantly, including developing such skills as suspending from branches and knuckle-walking.

"The common ancestor looked like Ardi. It's the chimp and gorilla that have evolved enormously, not hominids. Hominids have concentrated their evolution in two things -- upright walking and brain. Everything else is pretty primitive," Lovejoy said.

In the Ardipithecus genus, the males are not significantly different in size from the females. The males also lack the dagger-like teeth that male chimps use to fight one another for access to ovulating females. Lovejoy argues that this is a sign of a different social organization. The males, he argues, pair-bonded with females, and supplied them with food. The upright walking would have made food transport easier. Lovejoy sees male parental investment in the survival of offspring as a hallmark of the human lineage.

"The road to becoming human didn't start with a big brain. The road to becoming human began with setting the social conditions that would allow for the expansion of the big brain," Lovejoy said, reiterating a hypothesis he developed long before the discovery of Ardi.

Andrew Hill, a Yale anthropologist, said he didn't think there was enough evidence to support Lovejoy's conclusions about the domestic relations of male and female Ardipithecines. But he said the newly described hominid is a "very satisfactory animal" that "reinforces the accumulating evidence that these things probably evolved and really lived in woodland conditions rather than savannahs."

David Pilbeam, a Harvard paleontologist, noted that there has been some impatience in the scientific community as White and his team conducted the Ardipithecus analysis, but he suggested that the wait was worth it: "This is an extraordinary achievement, of discovery, recovery, reconstitution, description and analysis, which will keep many others busy for at least another 15 years."

Ardi did not look like a human by any stretch. She had a small head relative to her body size. There is no way to read her mind and measure her sense of self, her awareness of her place in the universe. But if the scientists are correct, her path in life proved to be fruitful over time, and the planet witnessed the rise of a new animal that could run on two legs, invent tools, tame fire, and perhaps eventually -- with much digging and scraping -- decipher its own origin.