Study co-author Smith said her research team knew that human ancestors living several million years ago grew up differently from modern children.
"What we didn't know was when the modern human condition of a long childhood and slow period of growth and development evolved," she said.
The study suggests that developmentally modern humans existed at least 160,000 years ago, which Smith says is just slightly younger than the earliest fossil Homo sapiens from East Africa.
Promising New Method
"It is a great result that today we can really measure growth rates of teeth due to CT [and] x-ray technology," said Professor Ottmar Kullmer, a paleoanthropologist at the Research Institute Senckenberg in Germany.
"These new possibilities of modern analysis methods augment the understanding of early Homo sapiens development and human evolution in general."
Kullmer, who was not a participant in the study, said that the discovery of a relatively long human childhood about 160,000 years ago points to "a complex social system in early Homo sapiens groups."
"Probably, social behavior was one of the important survival strategies of early humans."
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