Neanderthal Teeth Grew No Faster Than Comparable Modern Humans'

Theyfound that the rate of tooth growth present in the Neanderthal fossilsthey examined was comparable to that of three different populations ofmodern humans.

And since the rate of tooth growth has become amore-accepted tool for estimating the length of childhood amonghominids, the finding is the latest evidence suggesting thatNeanderthals may not have been as different from modern humans as someresearchers have thought.

The study by Debbie Guatelli-Steinberg,assistant professor of anthropology at Ohio State , appeared in thecurrent issue of the Proceedings of the National Academy of Sciences.Donald J. Reid, lecturer in oral biology at the University of Newcastle, Thomas A. Bishop, associate professor of statistics, and ClarkLarsen, professor and chair of anthropology, both at Ohio State , wereco-authors in the study.

“Based on our study of the enamel ofthese Neanderthal teeth and other modern ones, we can't support theclaim that Neanderthals grew up more quickly than do modern humans,”she said.

Key to this conclusion are microscopic lines on theoutside of teeth that mark the incremental growth of enamel on a youngtooth. Like tree rings that can gauge the age of a redwood, thesestriations – called perikymata – record new growth on the surface ofthe tooth.

Researchers know from earlier work that these markingsare present in all forming teeth, signifying six to 12 days of growth.By multiplying that interval by the number of perikymata on a tooth'ssurface, researchers can gauge how long it took for the tooth tomature. And that gives them an indication of the length of anindividual's childhood.

Neanderthals, Homo neanderthalensis, werethe dominant hominid inhabiting most of what is now Europe and westernAsia . Remains have been found as far south as Iraq and as far north asGreat Britain . Fossil skulls reveal the distinctively prominent browsand missing chins that set them apart from later humans.

Theythrived from about 150,000 to 30,000 years ago until their lineagefailed for as-yet unknown reasons. Most researchers have argued thattheir life in extremely harsh, Ice Age-like environments, coupled withtheir limited technological skills, ultimately led to their demise.

Ina study published last year in the journal Nature, other researcherscontended that Neanderthal teeth took 15 percent less time to reachmaturity than those in later Homo sapiens, suggesting to them that aNeanderthal childhood would be shorter than our own.

ButGuatelli-Steinberg's team wanted a broader comparison and thereforecompared the teeth from Neanderthals to those of three modernpopulations – people currently living in Newcastle-upon-Tyne , U.K. ;indigenous people from southern Africa, and Inuit from Alaska datingfrom 500 B.C. until the present.

“We chose these three groupssince they would provide a good cross-section of various populationsfrom different regions of the world,” she said. “We feel that they giveus some insights into the variation that exists within modern humans.”

Forthe study, the researchers used precise dental impressionsGuatelli-Steinberg and Larsen made of 55 teeth believed to come from 30Neanderthal individuals. These were compared to 65 teeth from 17 Inuit,134 teeth from 114 southern Africans and 115 teeth from as manyNewcastle residents. In all cases, the researchers tallied the numberof perikymata on the enamel surface of the teeth.

Guatelli-Steinbergsaid that the results showed that the enamel formation times for theNeanderthals fell easily within the range of time shown by teeth fromthe three modern populations – a conclusion that did not support ashorter childhood for the Neanderthals.

Enticing though it maybe, these new findings haven't convinced the researchers that aNeanderthal childhood was equal to a modern human's.

“The missingkey bit of data to show that would be evidence for when the first molartooth erupted in the Neanderthals, and we simple have no evidence ofwhen that occurred,” she said.

The length of time is important,the researchers say, because unlike all other primates, humans have anextended period of childhood growth, during which brain matures both insize and through experiences. Some earlier hominids matured far morequickly than modern humans.

“The question is when exactly did that pattern of development evolve in the growth of humans,” she said.

Supportfor this research came from a grant from the Leakey Foundation and fromthe College of Social and Behavioral Sciences at Ohio State .