A new theory suggests that prehistoric humans may have split from primates 2 million years earlier than what was previously believed.
The idea comes after scientists unearthed fossils of the Chororapithecus abyssinicus, the common ancestor of apes and humans, at the Chorora Formation in Ethiopia.
After analyzing the teeth fossils of the C. abyssinicus, researchers found that the remains were 8 million years old, evidently younger than the period when the human and ape lineage was thought to be cut.
Instead, the findings support early divergence between humans and primates. Humans split from gorillas 10 million years ago, while our ancient ancestors separated from chimpanzees 8 million years ago, researchers said.
"That's at least 2 million years earlier than previous estimates, which were based on genetic science that lacked fossil evidence," said Giday WoldeGabriel, a geologist from the Los Alamos National Laboratory.
Figuring Out The Age Of Volcanic Rock And Sediments
WoldeGabriel and his colleagues sifted through sediments and volcanic rock samples found above and below the Earth to narrow down the timeline for the C. abyssinicus teeth.
They estimated the age of the samples, which had enclosed the fossils, through argon-dating and paleomagnetic methods.
WoldeGabriel helped nail down the age of the fossils to 8 million years old through several methods: fieldwork, volcanic ash chemistry and geochronology.
Filling In The Evolutionary Gap
Gorillas, orangutans, chimpanzees and humans comprise the biological family Hominidae. Scientists' knowledge of how humans evolved away from the primate family tree has significantly improved in recent years due to the fossils excavated from Ethiopia.
Most of the senior members of the Chorora research team also work on projects for the Middle Awash team, which has recovered the remains of at least eight hominid species -- including some of the earliest hominids -- spanning roughly 6 million years.
Before the Chorora team unearthed the C. abyssinicus, the team recovered the nearly-intact fossils of the 4.4 million-year-old Ardipithecus ramidus or Ardi, and the fossils of the million-year-old Ardipithecus kadabba.
Researchers said these Ardipithecus species are the earliest known ancestors of humans after they split from the great ape lineage. These species were neither chimp-like nor ape-like, and they weren't human either. Despite this divergence, the species were both bipedal as they can walk upright.
While the team was still on the process of studying both Ardipithecus species, they had published their findings about the C. abyssinicus. Their fossil collection included nine fossilized teeth from multiple C. abyssinicus individuals, which were gorilla-like and seemed to be adapted for a fibrous diet.
Based on their research on the Ardipithecus species and the C. abyssinicus, the team concluded that the common ancestors of humans and apes lived earlier and the split had occurred 5 million years ago.
Additionally, the findings reveal that our common ancestors had migrated from Africa and not Eurasia. Although other experts say more evidence is required before the findings are acccepted, many scientists agree that the unearthing of a fossil from this time period is important because only other one of its kind has been found.
Meanwhile, WoldeGabriel and his team's findings are featured in the journal Nature.