for National Geographic News
Neandertals may have matured much earlier than modern humans—perhaps by as young as 15 years old, as opposed to 18 to 20 for modern humans, a team of scientists reports.
Researchers Fernando V. Ramirez Rozzi and José Maria Bermudez de Castro compared fossil teeth of Neandertals, anatomically modern humans, and two earlier species in the Homo genus (Homo antecessor and Homo heidelbergensis).
The researchers' results indicate that Neandertal growth patterns differed significantly from that of modern humans.
"Surprisingly, Neandertals were characterized by having the shortest period of dental growth," they write in the April 29 issue of the science journal Nature.
The difference in maturation rates is further evidence that Neandertals were a distinct species and that they were not our forefathers, the authors conclude.
"It's another piece of evidence that Neandertals were biologically very different than modern Homo sapiens, different enough to be a different species," said Gary T. Schwartz, a paleoanthropologist at Northern Illinois University. "Because they're growing so fast in a fundamentally different way, it essentially precludes them from being our ancestor."
Others disagree. Erik Trinkaus is a paleoanthropologist at Washington University in St. Louis. He argues that there are no established criteria or data for determining at what point different growth rates indicate different species.
The authors also do not take into account normal variation in growth rates, which are influenced by both genetic makeup and environmental factors, Trinkaus said.
"I think they grossly overinterpret the data," Trinkaus said. "A 10 or 15 percent difference in the rate of maturation is well within the normal variation of modern population."
"Even if Neandertals are growing a little faster, in terms of behavior, age of reproduction, and demography, I'm not convinced it would make a big difference," he said.
Tooth and Brain
A surprising amount of information can be gleaned from teeth. The rate at which teeth grow is linked to diet, brain size, gestation length, age of reproduction, and longevity.
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