Fossil suggests single human ancestor
Science News: Week of March 23, 2002; Vol. 161, No. 12
Fossils of H. erectus were discovered in Java in the 1800s. For many years, this species was recognized as the sole link between humans' earliest direct ancestor, Homo habilis, and modern Homo sapiens. H. erectus emerged 1.8 million years ago and may have survived to times as recent as 50,000 years ago.
Beginning in the 1980s, with the advent of new methods of analysis, some anthropologists have argued for splitting up H. erectus (SN: 6/20/92, p. 408). Proponents of this argument hold that European and African specimens formerly considered H. erectus belong to another species that they call Homo ergaster. They say that H. ergaster evolved into modern man but the Asia-bound H. erectus came up against an evolutionary dead end.
Arguments have raged, with some scientists proposing that observed differences between specimens are due to evolution in a single species over timemost African fossils are older than Asian onesrather than the presence of two distinct species.
The newfound specimen is younger than most African fossils assigned to H. ergaster and contemporary with some Asian H. erectus specimens, with which it shares striking similarities.
This is the first time that it's been possible to compare Asian and African fossils from the same period, says W. Henry Gilbert of the University of California, Berkeley, who discovered the fossil. The find may vindicate researchers who argued against dividing the species, he says.
The skullwhich is missing the lower face, jaw, and teethcomes from a fossil-rich region 140 miles northeast of Addis Ababa, Ethiopia. Scratch marks suggest that the individual may have been killed by a lion or hyena that ate the lower face and gnawed the skull in an attempt to extract the brain, says study coauthor Tim White, also of UC-Berkeley. Researchers spent 2 years cleaning the partially crushed skull.
With the new specimen in hand, White and his coworkers compared 14 groups of H. erectus and H. ergaster skulls from Asia, Africa, and Georgia, formerly in the Soviet Union. The researchers found a considerable overlap in shape between specimens from Asia and the other geographic regions, they report in the March 21 Nature. Features such as a short bulging forehead in the new fossil are similar to those in Asian H. erectus, says White.
Though most anthropologists are excited with the find, some disagree with the authors' conclusions. "The researchers should be congratulated on finding such a fantastic specimen," says Bernard Wood of George Washington University in Washington, D.C. However, they can't rule out that the new specimen is H. ergaster, he adds.
"I don't think this will conclude the debate," says Chris Stringer of the Natural History Museum in London. He points out that scientists who support dividing the species based many conclusions on dental features of H. erectus. These can't be compared with the new fossil because it's missing its teeth.
Others feel the fossil provides unequivocal evidence of a single species. "This slams the door shut [on the debate]," says C. Owen Lovejoy of Kent (Ohio) State University. "Now, all these specimens can be confidently restored to their original designation as H. erectus."
"This find should put the issue to rest," agrees Milford Wolpoff of the University of Michigan in Ann Arbor. However, he adds, "no discovery ever seems to put things to rest in a field as contentious as paleontology."
Asfaw, B., W.H. Gilbert, . . . and T.D. White. 2002. Remains of Homo erectus from Bouri, Middle Awash, Ethiopia. Nature 416(March 21):317-320.
Bower, B. 1992. Erectus unhinged. Science News 141(June 20):408.
W. Henry Gilbert
C. Owen Lovejoy
Tim D. White
Copyright: From Science News, Vol. 161, No. 12, March 23, 2002, p. 179.
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