for National Geographic News
Our prolonged childhoods make us Homo sapiens unique among primates. Scientists have a theory to explain this lengthy maturation process: Our brains need many years of learning and physical growth before we're equipped for the complexities of human living.
Now a new study says we weren't the only humans who took their time growing up. Analysis of Neandertal teeth suggests that the extinct species had similarly lengthy childhoods.
The study, published in the Proceedings of the National Academy of Sciences Online Early Edition, compared growth rates of Neandertal front teeth with those of three modern human populations: Inuit (Eskimo), English, and southern African.
Anthropology professor Debbie Guatelli-Steinberg of the Ohio State University in Columbus led the team. They found that Neandertal (often spelled "Neanderthal") teeth grew at a similar rate to those of people living today and actually formed slower than those of southern Africans.
The team says tooth growth correlates closely with other aspects of primate development, including life span and brain size.
"Neandertals also had large brains, so it makes sense that they took a long time to grow up, just as modern humans do," Guatelli-Steinberg said.
The team based their findings on layers of tooth enamel.
"Like trees, teeth grow in layers," Guatelli-Steinberg said. "These layers are visible under a microscope, and they represent anywhere from 6 to 12 days' worth of growth in humans. By counting these layers, one can estimate how long it takes for the enamel surface to form."
"It is clear that Neandertals were growing their teeth in comparable or even longer periods of time than some of the modern human populations we studied," she added.
The question of whether Neandertals, who died out some 35,000 years ago, shared the prolonged childhoods found in modern humans is a controversial one.
Other researchers who studied Neandertal tooth remains reported in 2004 that Neandertals became sexually mature adults by as young as 15 years of age (see "Neandertals Were Fully Developed by Age 15, Experts Say"). The 2004 study found Neandertal wisdom teeth grew 15 percent faster than those of modern humans.
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