New Fossils Found in Kenya Challenge Current Views on Early Evolution of Genus Homo
By James Devitt
Two new fossils discovered in Kenya cast fresh light on a little understood and important period of human prehistory at the dawn of our own genus, Homo. The new fossils were found by the Koobi Fora Research Project, directed by mother-daughter team Meave and Louise Leakey, and affiliated with the National Museums of Kenya (NMK). The finding suggests that human evolution did not occur in linear succession over two million years—from Homo habilis to Homo erectus to ourselves, Homo sapiens—but, rather, that Homo habilis and Homo erectus actually lived side by side in eastern Africa for nearly half a million years. An article on the findings, co-authored by NYU anthropologist Susan Antón, appeared last month in the journal Nature.
Homo erectus is commonly seen as the first human ancestor that is like 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.
One of the two fossils, an upper jaw bone, is the last known Homo habilis, dated to 1.44 million years ago. This late-survivor shows that Homo habilis and Homo erectus lived concurrently in eastern Africa for nearly half a million years.
“Their co-existence makes it unlikely that Homo erectus evolved from Homo habilis,” explained Meave Leakey, one of the lead authors of the paper. Instead, both species must have had their origins between 2 and 3 million years ago, a time from which few human fossils are known. “The fact that they stayed separate as individual species for a long time suggests that they had their own ecological niche, thus avoiding direct competition.”
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,” added Fred Spoor, a professor of evolutionary anatomy at London’s University College and another lead author. “It is the smallest Homo erectus found thus 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 neighboring Tanzania, almost rivals that shown by modern gorillas.
“In gorillas males are much larger than females, and this sexual dimorphism is partly related to their strategy of having multiple mates,” observed Antón, who is an associate professor of anthropology at the NYU’s Center for the Study of Human Origins. “The new Kenyan fossil suggests that, contrary to common belief, this may have been true of Homo erectus as well.”
Because great sexual dimorphism, or systematic differences in form, 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 Manthi. To establish the age of the two fossils, the geological layers were studied by Patrick Gathogo and Frank Brown of the University of Utah and Ian McDougall of Australian National University.
Antón directs NYU’s masters program in human skeletal biology, which prepared students for either doctoral programs or for applied work in forensic anthropology, such as careers as medical examiners, or in contract archaeology.
