Fossils alter an evolutionary theory

Bigger-brained babies led to a wider pelvis in females of the human ancestor Homo erectus, a sign that even 1.3 million years ago evolution began to favor intellectual capacity over physical mobility in people, researchers said.

Researchers earlier thought that females and males of Homo erectus had runners' bodies, tall and slender with narrow hips, providing comfort in a hot climate and speed to chase game across African plains. The discovery of female pelvic fossils has changed that notion.

Because of earlier reliance on male pelvic fossils, scientists had estimated the brains of Homo erectus measured about a half-pint at birth. The female fossils show the newborns' brains were about 30 percent larger, said researchers led by Scott W. Simpson, an anthropologist at the Case Western Reserve University School of Medicine in Cleveland.

The species' skeleton was "substantially modified by the demands of birthing large-brained offspring," the authors concluded in their study.

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