The oldest known member of the human genus has been discovered in Ethiopia, potentially revealing details about the lineage of our most ancient direct ancestors. Analysis shows that individuals in the genus Homo may have walked the Earth 400,000 years before archaeologists previously believed.
The Ledi-Geraru jawbone examined is believed to be roughly 2.8 million years old, while the oldest sample from a species within the Homo genus, or family, was thought to date from 2.4 million years in the past. The specimen includes the left side of the lower jaw, along with five graying teeth.
Africa is a rich territory in which to find many ancient human fossils, but examples dating to between 2 and 3 million years ago are difficult to locate.
This fossil came from a time when human ancestors were evolving through a critical transition from ape-like Australopithecus to the highly-intelligent form we have taken today. In 1974, the fossilized remains of an Australopithecus named Lucy brought attention to studies of distant human ancestors.
The individual lived out its life around the time of a major climate shift on that area of the African continent. Arid savannahs began to displace forests, and larger waterways began to dry up, leaving behind smaller ponds and lakes, many of which were filled with crocodiles. This latter environment is much like that seen in the region in the modern day.
Such environmental changes, combined with evolutionary adaptations, may have resulted in a change in diet for the early Homo species, who likely began to consume more meat than earlier human ancestors. Stone tools were another adaptation of this distant human ancestor, which lived around 200,000 years after the last Australopithecus walked the Earth.
Features in the jaw, including an evenly-proportioned jaw, slim molars, and symmetrical premolars, differentiate this creature from Australopithecus. However, a sloping chin is similar to earlier ancestors than more modern relatives to contemporary humans, researchers concluded.
"The Ledi jaw helps narrow the evolutionary gap between Australopithecus and early Homo. It's an excellent case of a transitional fossil in a critical time period in human evolution," William Kimbel of the Institute of Human Origins at UNLV said.
Analysis of the jaw bone could help answer questions about how our distant ancestors lived. The discovery of the Australopithecus Lucy reveled vast amounts of previously unknown data on her species, which was the first human ancestor to walk upright.
Discovery of the ancient member of the Homo genus, and analysis of the fossil, was detailed in the journal Science.