for National Geographic News
Early humans were giving birth to big-brained infants much earlier than previously thought, suggests the most intact pelvis from a Homo erectus female ever found.
The 1.2-million-year-old fossil pelvis was unearthed in Ethiopia in 2001 and is about 85 percent complete, a new study reports.
Prior to the find, the earliest direct evidence that scientists had of a human or human ancestor—also called a hominin—giving birth to babies with big brains was 400,000 years ago.
Past reconstructions based on less complete fossils had indicated H. erectus females had narrow hips and gave birth to infants with relatively small brains.
But the larger size and broader shape of the new pelvis indicates the skulls of H. erectus infants may have been 30 percent larger than past skeletal reconstructions suggests.
Consequently, H. erectus would have been more developmentally mature at birth than previously suspected, said study leader Scott Simpson of Case Western Reserve University in Cleveland, Ohio. His team's research will be detailed in the November 14 issue of the journal Science.
"It's not that they come out walking and talking and fending for themselves, but they were not as helpless as we see in modern humans," he said.
H. erectus infants also grew faster than modern babies, and were probably weaned from their mother's milk sooner, Simpson added.
"That means they could be incorporated into the society at very young ages," he said.
The new findings suggest that the brain size of an H. erectus infant was already 30 to 50 percent that of an adult. By contrast, modern babies are born with brains that are only about a quarter the size of an adult human's.
So even though the brains of modern humans are bigger at birth than H. erectus's, modern babies are less mature.
Related: "'Lucy's Baby'—World's Oldest Child—Found by Fossil Hunters" [September 20, 2006].)
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