Stone Age gal had wide hips: H. erectus females may have delivered big-brained babies

Science News, Dec 6, 2008 by Bruce Bower

She was short, squat and definitely not built for speed. On the plus side, this adult female Homo erectus, who lived in Africa roughly 1 million years ago, had hips wide enough to bear babies with brains nearly as big as those of newborn human infants.

That's the evolutionary picture presented by researchers who have unearthed a rare find: a nearly complete female H. erectus pelvis. Pieces of the fossil were found at an Ethiopian site called Gona in 2001 and 2003.

H. erectus females evolved a pelvis of a size unprecedented among human ancestors because the females had to squeeze increasingly big-headed babies through their birth canals, concludes a team led by anthropologists Scott Simpson of Case Western Reserve University in Cleveland and Sileshi Semaw of Indiana University in Bloomington. Given the size and shape of the new pelvis, H. erectus infants must have been more than 30 percent larger at birth than has usually been assumed, the scientists contend.

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In the Nov. 14 Science, the researchers say that the new pelvis challenges a proposal that both sexes of H. erectus evolved to grow relatively tall and slender to shed body heat more efficiently in their tropical-homelands. That idea was based largely on measurements of an H, erectus skeleton found in 1984 and attributed to a slim, 10-to 12-year-old boy who would have stood an estimated 6 feet, 2 inches as an adult.

The broad, flaring pelvis also challenges an earlier proposal that H. erectus individuals possessed narrow hips suitable for endurance running, a capacity that would have aided them in hunting.

"It's now apparent that body size range in H. erectus has been underestimated," Simpson says. The Gona female stood no taller than 4 feet, 9 inches.

"I do not see any major problems with either the reconstruction or the interpretation of this new specimen," comments anthropologist C. Owen Lovejoy of Kent State University in Ohio.

But Harvard University anthropologist Daniel Lieberman disagrees. "This pelvis is a nice addition to the fossil record, but it raises more questions than it answers," he says. In his view, the new specimen might come from a male of a comparably ancient species in the human evolutionary family.