He had a small face, small teeth, a narrow head, a very heavy brow and he could be your oldest ancestor.
A team of French and Chadian researchers announced today they have found the skull, jaw fragments and teeth of a six million to seven million-year-old relative of the human family. The find, which is the oldest human relative ever found, suggests humans may have begun evolving from chimpanzees sooner than researchers realized.
It also implies that human evolution may have been a much messier process than imagined.
"What this does is say 'Hey, where humans are connected to the tree of life is not a simple connection,'" says Bernard Wood, an anthropologist at George Washington University.
The skull's human-like face and teeth are surprising since they come from a period when researchers believed human ancestors just began evolving. Many expected a specimen as old as this one — named Toumaï — to appear more chimp-like.
Instead, Wood explains, species like the Chad discovery may have been among several early versions of human ancestors. That would mean the tree of life may be more "bushy" than tree-like, with several branch species diverging from the ancestral line.
A Life's Work
An international team led by French paleontologist Michel Brunet found the unusually complete skull, two lower jaw fragments and three teeth last year in Chad, Central Africa. Brunet, who has spent the last 25 years searching in the region, delayed announcing the discovery since he first wanted to consult with colleagues and ensure his estimations of the specimen were accurate.
"It's a lot of emotion to have in my hand the beginning of human lineage," Brunet told Nature magazine, where his reports about the skull appear this week. "I have been looking for this for so long."
The skull shows both chimp and human-like features, but is clearly a member of the hominid family — the family including species more closely related to humans than chimpanzees. Brunet called the find Sahelanthropus tchadensis — referring to the discovery site in Chad, in Africa's Sahel region and nicknamed it "Toumaï," "hope of life" in Africa's Goran language.
Whether Toumaï is a direct ancestor of humans remains to be seen and may be unlikely.
"I have my doubts this is our direct ancestor simply because the first time someone puts their hand in a pie, they're not likely to pull out the plum," says Wood.
The "pie," so to speak, is the time period of six million to seven million years ago.
Vital Piece of the Puzzle
The well-preserved skull of Toumaï adds valuable information to a time period in human evolution that is still fuzzy. Archaeological evidence suggests the world was populated by apes 10 million years ago, then fairly complete fossil records show early ancestors of humans began appearing on the scene about five million years ago.
Few fossils have filled in the gap between these two time periods.
Scientists had assumed that human ancestors began splitting from chimpanzees about five million to seven million years ago, based on genetic evidence. Toumaï's appearance pushes that timeline back and suggests that nature may have begun experimenting with human evolution at least a couple of million years earlier.
The Chadian skull is twice as old as "Lucy," the fossilized hominid found in 1974 in Ethiopia that was once considered the mother of all humanity. It's also older than the 5.8-million-year-old controversial remains known as "Millennium Man" that were found in Kenya in 2000 and older than the 5.8 million-year-old teeth and bones found in Ethiopia last July.
"The reason the fossils and their contexts are important is that it is only through these and their proper analysis that we can come to truly know our past," explains Tim White, an anthropologist at the University of California at Berkeley who led the excavation of the 5.8-million-year-old hominid teeth and bones in Ethiopia.
The 'Wrong' Side of the Valley
The wind-seared location of the Toumaï find was also unusual and challenges the theory that human ancestors evolved on the east side of the African Rift Valley while apes evolved on the west.
The valley formed eight million years ago when a geologic fault collapsed into the earth. On the east side, the climate became arid and forests turned to dry grasslands. Scientists had assumed that humans evolved here since there were no trees to offer high vantage points. In order to see over the grass, early humans would need to walk upright.
Brunet's 40-member team unearthed Toumaï from the western side of the valley that had remained lush with trees and lakes millions of years ago.
They also found signs of ancient crocodiles, snakes and turtles in the region. Brunet dated plant and animal remains in the soil around the fossils to settle on the approximate age of the hominid. While other scientists appear to accept Toumaï's estimated age of six to -seven million years, they remain surprised by the ancient hominid's looks.
Strange Mix of Features
"Sahelanthropus tchadensis shows a mix of primitive and evolved characteristics never seen before," says Chris Stringer, an anthropologist at the Natural History Museum in London.
Some argue, for example, that Toumaï's small face and teeth appear more modern than Lucy, the 3-million-year-old hominid skeleton. While his face may appear modern, Toumaï's skull is long and narrow and once held a small, chimpanzee-sized brain.
Perhaps most striking is the skull's brow line, which is remarkably large. Brunet explains the large brow line is what suggests Toumaï was male since it's a common male trait that's thought to help attract females.
"My guess is the competition between these early hominids was intense and natural selection favored males with large brow ridges," says David Pilbeam, a Harvard University anthropologist and a co-author of the Nature study.
Brunet's team did not find any leg bones of Toumaï but the point where his spinal cord entered his skull suggests Toumaï likely walked upright. Spinal cords in humans connect at the bottom of the skull since they carry themselves and their heads in a vertical line.
He may have walked on two feet but researchers say it's difficult, if not impossible, to know if this ancient hominid was a direct ancestral link to humans or possibly a false start within the apparently complex "bush" of life.
"There are lots of new questions," says Brunet. "This is just the beginning of our knowledge of the human lineage."