Neanderthals first appeared in Europe about 300,000 years ago but mysteriously vanished about 35,000 years ago, shortly after the arrival of modern humans in Europe.
The University of Zurich's Marcia Ponce de León and colleagues pieced together three Neanderthal skeletons: one newborn from Mezmaiskaya Cave in Russia and two infants aged 19 and 24 months, respectively, from Dederiyeh Cave in Syria.
In addition, the scientists reconstructed the pelvis of an adult female Neanderthal skeleton, found in Tabun Cave in Israel.
(See a map of the Neanderthals' range.)
By analyzing the skeletons, the team found that Neanderthal babies were born with similar-size skulls to those of modern human babies. However, the shape of the face was different.
"Even in a newborn [Neanderthal] baby, we could see the conspicuous protrusion of the forehead that distinguishes Neanderthals," said study co-author Christoph Zollikofer, also of the University of Zurich.
By creating virtual reconstructions of the Neanderthal skeletons, the scientists also investigated the birthing process.
"The birth would have been at the limit of what was possible, and the baby's head would have had to turn by a quarter in order to get through the narrow lower pelvis," Zollikofer said—as is required of the smaller-headed babies of modern humans.
Young Neanderthals' rapid growth required lots of energy, experts say.
"Neanderthals must have had a rich diet in protein and fat for children to fuel rapid growth in [their] brains," said Holly Smith of the Museum of Anthropology at the University of Michigan, who was not involved in the research.
Mothers also likely had to consume vast quantities of calories to produce enough breast milk.
This energy-intensive child rearing may have caused "somewhat longer interbirth intervals, or somewhat older mothers," study co-author Zollikofer said.
This may explain why modern humans eventually outcompeted Neanderthals.
(Read: "Neandertals Hunted as Well as Humans, Study Says" [January 25, 2006].)
"If one population reproduces just one percent more than another, then it can eventually replace the other population," Zollikofer said.
However, Dean of University College London is not convinced by this argument.
"I think they might be trying to push their data too far," he said.
SOURCES AND RELATED WEB SITES