Philip Ngunjiri
21 August 2007
Nairobi — A National Museums of Kenya scientist has found a human fossil that has forced scientists to radically revise accepted notions of the sequence of our evolution from the early hominids, writes PHILIP NGUNJIRI
TWO NEW FOSSILS Discovered in Kenya have cast fresh light on a little understood period of human prehistory at the dawn of our own genus, Homo.
Dr Fredrick Kyalo Manthi's discovery, shows that extinct hominid (human-like) species - homo habilis and homo erectus - lived together in Illeret location of Marsabit district about two million years ago.
Before the find, evolutionists had believed that the two species lived in different epochs and had succeeded each other, with homo habilis giving way to homo erectus, from whom humans - homo sapiens - emerged.
Announcing the find at the National Museums of Kenya in Nairobi -which already hosts unmatched hominid and fossil collections in this part of the world - Dr Manthi said he had discovered the first two specimens in 2000 and expected the find to stir fresh debate on human origin.
The new fossils were discovered under the auspices of the Koobi Fora Research Project, an international group of scientists directed by mother-daughter team Meave and Louise Leakey, and affiliated with the National Museums of Kenya (NMK).
Human evolution over the past two million years is often portrayed as a linear succession of three species: Homo habilis to homo erectus to ourselves, homo sapiens. Of these, homo erectus is commonly seen as the first human ancestor similar to us in many respects but with a smaller brain.
"The new fossils are significant because both their relative geological ages and their physical attributes directly challenge these views about our human ancestry," said Meave Leakey in the article in Nature.
One of the two fossils, an upper jaw bone of homo habilis (KNM-ER 42703), dates from 1.44 million years ago, which is more recent than previously known fossils of that species. This late-survivor shows that homo habilis and homo erectus lived side by side in East Africa for nearly half a million years.
"Their co-existence makes it unlikely that homo erectus evolved from homo habilis," explains Meave Leakey.
Instead, both species must have had their origins between two and three million years ago, a period from which few human fossils have been found.
"The fact that they stayed separate as individual species for a long time suggests that they had their own ecological niches, thus avoiding direct competition," the journal says.
The second fossil (KNM-ER 42700), found in the same region of northern Kenya, is an exquisitely preserved skull of homo erectus, dated to about 1.55 million years ago.
"What is truly striking about this fossil is its size," says Fred Spoor, another lead author of the article in the journal. "It is the smallest homo erectus found so far anywhere in the world."
Significantly, the variation in size of East African homo erectus fossils, from the petite new skull to a large specimen discovered previously at Olduvai Gorge in Tanzania, almost rivals that shown by modern gorillas.
"In gorillas, males are larger than females, and this sexual dimorphism is related to their strategy of having multiple mates," says co-author Susan Anton.
"The new Kenyan fossil suggests that contrary to common belief, this may have been true of homo erectus as well."
Because great sexual dimorphism is thought to be a primitive, or ancestral feature during human evolution, the diminutive new find implies that homo erectus was not as human-like as once thought.
Both human fossils were found during fieldwork in 2000, in the Ileret region, east of Lake Turkana. The homo erectus skull was exceptionally well preserved, because it was still almost entirely encased in sandstone when it was initially spotted by NMK researcher Fredrick Mwanthi. Painstaking laboratory preparation at the NMK by Christopher Kiarie was required to free the fossil from its sediment. To establish the age of the two fossils, the geological layers were studied by Patrick Gathogo, Frank Brown, and Ian McDougall.
The National Geographic Society of the United States has sponsored Kenyan palaeontological fieldwork by the Koobi Fora Research Project in the Lake Turkana Basin since 1968. Meave and Louise Leakey are both Explorers in Residence at the National Geographic Society.
Thrilled by the recent discovery, NMK director-general, Dr Idle Farah, said it shows that the story of human evolution is not yet over and that there are still missing links for scientists to research.
NMK is planning travelling exhibitions in which funds generated from the public display of the unique collections will be used to fund research.
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