The fossilized pelvis of a Homo erectus woman who lived 1.2 million years ago on the banks of an Ethiopian river has been discovered, and while researchers say it casts new light on human evolution, some of their conclusions are challenging previous theories about these early human ancestors. The pelvis reveals a short, squat woman who wasn't built for long-distance running, but also a woman with a wide birth canal to accommodate big-brained infants. Study coauthor Scott Simpson says the pelvis's wide birth canal indicates that hominds' increasing brain size was a driving factor in human evolution.
Getting through the birth canal is "the most gymnastic thing we ever do," he says. To accommodate big-brained babies, humans must have developed larger and wider birth canals over time, but with few pelvic fossils, researchers had little idea when these changes began. The Busidima pelvis shows that a wide birth canal was already in place 1.2 million years ago [New Scientist].
The findings, published in Science [subscription required], seems to contradict an earlier theory on the appearance of these hominids:
H. erectus females were assumed to have had narrow hips and relatively small birth canals that could allow the passage of only small-brained infants. But such theories were largely based on measurements of the pelvis of "Turkana Boy," a 1.5-million-year-old juvenile male H. erectus fossil discovered in Kenya in 1984 [National Geographic News].
Simpson says it was difficult to make broad assumptions based on the Turkana Boy; the fossil was very fragmented, he says, and men and women can have very different anatomical features. Researchers say the newly discovered pelvis belonged to a woman in her 20s who stood about 4 feet 5 inches tall. This also challenges previous theories, as the Turkana Boy was thought to be over 6 feet tall, with a long and lean frame well suited for distance running. Anthropologist Daniel Lieberman says that earlier find led to the theory that
long-distance running enabled H. erectus to hunt effectively without spearheads and to obtain enough meat to support the evolution of increasingly large brains. “This pelvis is a nice addition to the fossil record, but it raises more questions than it answers” [Science News],
says Lieberman. With such divergent views on the table, Lieberman and some other experts say Simpson needs more evidence to support his theories. Related Content: 80beats: Neanderthal Mothers Had It Tougher Than Modern Moms DISCOVER: The Third Man explains how Homo erectus fossils have confused theories of human evolution Image: Scott Simpson