New fossils hint at ancestral split

African discoveries point to two early species in the human genus

Newly discovered face and jaw fossils show that at least two species of the human genus Homo lived alongside each other in East Africa nearly 2 million years ago.

ANCESTRAL MOUTHFUL A nearly 2 million-year-old lower jaw discovered recently in East Africa, along with other new finds, differs substantially from smaller, earlier discoveries of Homo fossils in the region, a new study finds. Mike Hettwer, courtesy of National Geographic

These new finds are a good match for a roughly 2 million-year-old Homo brain case and face excavated in 1972 in the same part of East Africa, reports a team led by anthropologist Meave Leakey of the Turkana Basin Institute in Nairobi, Kenya. Long considered a puzzling exception among early Homo finds, the 1972 discovery features big bones and a flat, upright face and represents a species apart, Leakey and her colleagues conclude in the Aug. 9 Nature.

Until now, researchers have found it difficult to exclude the possibility that the large-faced fossil — known as KNM-ER 1470 — came from a male of the same species as smaller, early Homo finds in East Africa.

“After so many years of questions about the identity of the enigmatic 1470 fossil, the chances that it’s from a separate species have greatly improved with our new discoveries,” says anthropologist and study coauthor Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Leakey and her colleagues unearthed the new fossils from 2007 to 2009 along the shore of Kenya’s Lake Turkana. Previously dated volcanic ash layers at the site place the finds at between 1.78 million and 1.95 million years old. Further study is needed before assigning the early Homo fossils to particular species, Spoor says, and it’s unclear whether either species led to Homo erectus or to people today. For now, he proposes only that at least two Homo species inhabited East Africa nearly 2 million years ago.

Anthropologist Bernard Wood of George Washington University in Washington, D.C., suspects that Leakey’s team has found fossil evidence for a new, early Homo species distinct from both the 1470 specimen, which he classes as H. rudolfensis, and other Homo fossils from that time, which he groups under H. habilis. The newly found face fossil, which belonged to a child about 8 years old, mirrors the shape of the adult 1470 face, Wood says. But the nearly complete lower jaw and partial lower jaw that Leakey’s team found fit neither in H. rudolfensis nor in H. habilis, he contends.

Evolutionary scientists disagree about whether early Homo fossils can be grouped even into those two species (SN: 3/1/03, p. 131).

Like Wood, anthropologist Donald Johanson of the Institute of Human Origins at Arizona State University in Tempe regards the new face fossil, from the child, and the 1470 fossil as H. rudolfensis. Homo split into at least three African species, including Homo erectus, by about 1.7 million years ago, Johanson says. His team previously excavated the earliest known Homo fossil, an upper jaw from Hadar, Ethiopia, that dates to 2.4 million years ago.

Even Spoor’s proposal that at least two species inhabited East Africa 2 million years ago goes too far, contends anthropologist Tim White of the University of California, Berkeley. Too few early Homo fossils exist to rule out whether the new finds, and the 1470 specimen, fall within a single species that included substantial skeletal differences across individuals and between sexes, White says.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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