WEDNESDAY, July 10, 2002 (HealthDayNews) -- Scientists have discovered what they say are the top of a pre-human skull, lower jaw fragments and teeth that are almost 7 million years old, nearly three million years older than previously discovered hominid fossils.
The discovery in the central African nation of Chad means the human race apparently diverged from chimpanzees far earlier than had been thought, according to the researchers.
Details of the discovery by a team of researchers from Chad and France are contained in two articles that appear in tomorrow's Nature.
Michel Brunet, study author and director of the 20-year research program that led to the findings, says, "This is the oldest hominid. It's 7 million years old, so the divergence between chimp and human must be even older than we thought before."
"This is one of the most important discoveries in paleontology in the last 100 years," says Daniel Lieberman, a Harvard University anthropologist who has seen the fragments, although he was not a member of the team that discovered them.
What's important about the discovery, Lieberman says, is the fragments' age, between 6 million and 7 million years old -- three million years older than all the pre-human fossils found so far.
Also, they were found a fair distance -- about 1,500 miles -- from the site of previous pre-human fossil discoveries at the Rift Valley in northern Chad, which means the earliest members of the human race could have been more widely dispersed than previously thought.
Third, the discovery sheds light on the history of human evolution, Lieberman says. Ten million years ago, according to the Nature articles, the world was full of apes. The first good indications of pre-humans on the planet didn't surface until more than five million years later. In the intervening five million years, the human lineage diverged from that of the chimpanzee, but little is known about how that happened, the articles say.
The hominid fragments have been named "Toumai," which means "Hope of Life" in a language of Chad. They were found last summer in the Djurab Desert in the northern part of the country, the researchers say.
The fossils indicate that Toumai was probably a male, with a thick brow, and teeth that varied in size and thickness from both chimpanzees and other early pre-human fossils. It was probably the size of a modern chimpanzee. The size of the brain case is also similar to that of modern chimps, according to the researchers.
Interestingly, Toumai has more human characteristics than pre-human fossils of more recent origin: "Its face is much more modern than more recent fossils," Lieberman says.
This suggests there's much to be learned about how and when the evolutionary divergence between humans and chimps began, he says.
Because only the top of the skull and lower jaws and teeth were found, further analysis is needed to assess how Toumai looked and moved -- for instance, if it walked upright or on all fours, the researchers say.
The age of the Toumai fragments was determined by using a palaeoecological study of fauna in the area where the fossils were found. The study revealed aquatic life, as well as evidence of animals that lived in forests and savannahs. This scientific process, called biochronology, suggests that Toumai lived between six and seven million years ago in an area close to a lake, but not far from a sandy desert, the researchers say.
Bernard Wood is an anthropologist at George Washington University who wrote an essay to accompany the articles in Nature. He says the Toumai "is certainly a good candidate for being the ancestor of all later hominids, and of the few fossils known from this time it is the best fit to an ancestor."
"But it is also possible that it is a cousin of later humans, and that it's human-like features evolved in parallel with our own," he adds.
What To Do
To learn more about human evolution, visit this PBS site. And a chart of human evolution that doesn't include the Toumai discovery can be found at Handprint.
