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UD anthropologist finds signs of evolution in ancient skeleton

Karen Rosenberg, chairperson and associate professor of anthropology at UD
10:03 a.m., March 2, 2006--Recent analysis of a Stone Age skeleton shows that human brain size relative to body size had increased dramatically from ancestors by the Middle Pleistocene, about 260,000 years ago, Karen Rosenberg, chairperson and associate professor of anthropology at the University of Delaware, said.

Rosenberg, who analyzed the fossil with Lü Zuné of Peking University in Beijing and Chris B. Ruff, director of the Center for Functional Anatomy and Evolution at the Johns Hopkins University School of Medicine in Baltimore, said the female skeleton, which was found at a site called Jinniushan in northeastern China 22 years ago, sheds new light on human evolution.

“This fossil belonged to one person from a time and place we didn't know very much about,” Rosenberg said. “What we were really interested in was what could this person tell us about relative brain size [and] body shape, and we could look at all of that in this specimen.”

Rosenberg said the skeleton is exceptionally useful because it includes a nearly complete skull, vertebrae, a hip bone and an arm bone from a single human, features that enabled the scientists to evaluate skeletal evidence for body shape and relative brain size in an individual rather than relying on samples from separate individuals from multiple regions.

In a report published Feb. 27 in Proceedings of the National Academy of Sciences, Rosenberg's team writes: “Because the Jinniushan specimen preserves both postcranial remains and a fairly complete skull, we have the unusual, if not unique, opportunity to examine the relationship between body size and cranial capacity in this Middle Pleistocene individual. Most estimates of brain size have been carried out by using brain size estimates and body size estimates from different specimens or have used body size estimates derived from cranial dimensions, which are less accurate and subject to possible circular reasoning.”

Rosenberg's team found that the fossil shows not only that the skeleton's relative brain size fits the model of increasing brain size during the Middle Pleistocene throughout the human range, but that the skeleton's body proportions reflect a pattern of climatic adaptation that persists to the present day.

“As is typical of living cold-adapted peoples, her body size was very large and her broad body shape also gave her a relatively low surface-to-volume ratio,” Rosenberg said. “Long linear bodies are adapted to get rid of heat and can be found in warmer climates while short, stocky bodies are adapted to retain heat.”

The report states that the Jinniushan specimen shows that humans living around the cold region, which is now in northeastern China, near North Korea, had large, broad bodies with short limbs to enable them to retain more heat.

“In modern humans, populations from cold regions have relatively shorter limbs and wider bodies than those from warm regions,” the paper states, citing a comparison of the characteristics of skeletons from East Africa and inhabitants of the Arctic region. “As expected, cold-adapted modern populations have relatively shorter ulnas [a bone in the forearm] for their trunk diameters than warm-adapted populations. Pre-Holocene humans from higher and lower latitudes follow the same pattern as modern humans.”

Rosenberg, who studied the skeleton in China and uses a replica of the pelvis to explain some of her findings, said her experience has been a great benefit to her students. “The fact that I worked firsthand with the fossils is very important to the students; it makes it all real, which is especially important at a time when some people are questioning the scientific basis for evolution,” she said.

A graduate of the University of Chicago, Rosenberg received her doctorate in biological anthropology from the University of Michigan and joined the University of Delaware in 1987.

Article by Martin Mbugua
Photo by Kathy F. Atkinson

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