Ancient reproduction gets pelvic thrust.

Human ancestors who lived from millions to tens of thousands of years ago are succumbing to the pelvic examinations of scientists and yielding new insight into the evolution of reproduction and birth.

The reconstructed pelvis of the Australopithecine (the genus preceding Homo) dubbed Lucy, who is about 3.5 million years old, indicates that she could have delivered a baby the size of a newborn chimpanzee, report anthropologists Robert Tague and C. Owen Lovejoy of Kent (Ohio) State University. But giving birth would not have been as easy for Lucy as some researchers have suggested, said Tague last week at the annual meeting of the American Anthropological Association (AAA) in Washington, D.C.

"We don't know how large Australopithecine fetuses were," notes Tague, "but it's not unreasonable to assume a chimp-sized fetus could have been delivered. The birth process, however, would have been slower and more difficult [for Lucy than for a chimpanzee]."

Tague and Lovejoy compared the ancient female pelvis with modern female pelvises from chimpanzees and humans. Lucy, who was about 3 feet 8 inches tall and weighed around 65 pounds, has a "potentially spacious pelvis," says Tague. It is 12 percent smaller than the chimpanzee pelvis and appears to have been evolving in the direction of the modern human pelvis. But it is not narrow enough to suggest that Australopithecines had gestations as short as the nine months of modern females, resulting in the birth of babies requiring extended parental care, says Tague.

Scientists who found a 1.6 million-year-old male Homo erectus skeleton last year recently reported that measurements of his pelvis suggest that females of his species had narrow birth canals and accelerated births.

This fits into new data on the Neanderthal pelvis, presented at the AAA meeting by anthropologist Karen Rosenberg of the University of Michigan in Ann Arbor. "The birth canals of Neanderthals [who lived from about 125,000 to 35,000 years ago] are the same size as those of modern females of the same body weight," she reports. "There is no evidence for major reproductive changes from Neanderthals to modern humans."

Rosenberg first measured the pelvises of females in several modern human populations of different body proportions. Females who are heavy relative to their height, such as Alaskan Eskimos--whose body size is similar to that of the slightly heavier Neanderthals -- had the largest birth canals. The pelvises of three Neanderthal females indicate, says Rosenberg, that their birth canals were the same size as those of comparably heavy modern females.

Although Neanderthal mothers were heavier than their current counterparts, she says, birth canals and gestation periods of the two groups are comparable.