Sunday Newscape Magazine

Tucson, Arizona - Between 900,000 and 1.8 million years ago, Homo erectus made an evolutionary leap to develop brains closer in size to the large brains of modern-day man at birth, according to new research.

Researchers have figured out that Homo erectus was brainier than previously thought by analyzing the nearly complete female pelvis of a 1.2 million-year-old H. erectus found in the region of Gona, Ethiopia.

It's the most complete female pelvis of Homo erectus ever found.

Jay Quade, a UA professor of geosciences, was on the research team. His analyses were crucial in determining the age of the fossil, called the Busidima pelvis.

"It was a nice little geo-detective challenge," Quade said.

Lead author Scott Simpson of Case Western Research University in Cleveland, Ohio, determined the birth canal in the ancient pelvis could deliver a baby with a brain almost comparable to that of a modern-day baby of about 36 weeks gestational age.

The baby's brain could have been up to 315 cubic centimeters at birth, Simpson estimates.

Previously, scientists had thought Homo erectus brains were no larger than 230 cubic centimeters at birth. Modern-day human babies have brains about 380 cubic centimeters at birth.

But having the bone is just part of the analysis. Without knowing the age of the fossil or what that past environment was like, anthropologists can tell only part of the story.

"The fossil doesn't speak for itself," Simpson said. "Jay has been instrumental in not only telling us how old the fossil is, but in trying to reconstruct the habitat."

Quade's analyses show that this Homo erectus female lived in a grassland.

"We are still trying to figure out the connection between habitats and human evolution," Simpson said. "Because of Jay's careful research, we've been able to reconstruct these habitats with great fidelity."

Previously, the most complete Homo erectus fossil from that time period was found in Kenya, a young male, perhaps between ages 9 and 12, known as Turkana Boy. Scientists have estimated that at adulthood he would have been a slender male about six feet tall and that his female counterpart would have had a narrow pelvis. That would be consistent with the hypothesis that hominid pelves were evolved for endurance running in arid tropical grasslands.

However, Simpson said the new fossil shows that Homo erectus pelvises were evolving to be able to give birth to a larger-brained baby. He says the female of the Busidima pelvis would have been short and wide, not tall and slender, suggesting that Homo erectus males and females were very different in height at that time.

Simpson, Quade and their co-authors are publishing their paper, "A Female Homo erectus Pelvis from Gona, Ethiopia," in the Nov. 14 issue of the journal Science. The research team leader is Sileshi Semaw of Indiana University in Bloomington. The other authors are Naomi Levin, a former UA graduate student who is now at California Institute of Technology in Pasadena; Robert Butler of the University of Portland in Oregon; Guillaume Dupont-Nivet of Utrecht University in the Netherlands; and Melanie Everett of Indiana University.

The fossil was found weathering out of the silty sediment on a hillside that was once the ancient riverbed of the nearby Busidima River, Quade said.

The team used several different techniques to determine the fossil's age and what that ancient environment was like.

In one test, the researchers took samples from ancient volcanic ash that protruded from the hillside above and below the fossil. The layer above the fossil would have been deposited after the fossil and therefore younger than the fossil. Similarly, the layer below the fossil is older than the fossil.

Analyzing the chemical composition of the two ash layers using the electron microprobe at UA's Lunar and Planetary Laboratory narrowed the fossil's age to between 750,000 and 1.6 million years ago.

The team then used paleomagnetic data to double-check the dates. The date range for the fossil from the magnetic data matched that from the ash layers.

To narrow down the age further, the researchers figured out how fast sediment would have been deposited between the time the lower and upper volcanic ash layers were deposited.

The scientists then calculated how much time it would have taken to deposit a meter of sediment above the lower ash layer. By measuring up from the lower ash layer to the fossil, they estimated that the fossil was 1.2 million years old, give or take 200 thousand years.

Co-author Naomi Levin's UA master's thesis was about reconstructing the ancient environment of the area.

Levin and Quade analyzed the geochemical composition of the caliche and of animal teeth found in the same layer as the fossil pelvis. The animals present included the ancestors of modern elephants, antelopes, giraffes, hippos and crocodiles.

"From the point of view of chemical composition, you are what you eat," Quade said. "It was all grass out there."

Homo erectus of the time did live in a grassland, he said, but the new finding indicates that the stature and shape of those hominids was different from previously believed.

The Leakey Foundation, the National Geographic Society, the Wenner-Gren Foundation and the National Science Foundation funded the research.