Neanderthal Teeth Grew No Faster Than Comparable Modern Humans’
ScienceDaily (Sep. 20, 2005) —
COLUMBUS , Ohio – Recent research suggested that ancient Neanderthals might have had an accelerated childhood compared to that of modern humans but that seems flawed, based on a new assessment by researchers from Ohio State University and the University of Newcastle .
They found that the rate of tooth growth present in the Neanderthal fossils they examined was comparable to that of three different populations of modern humans.
And since the rate of tooth growth has become a more-accepted tool for estimating the length of childhood among hominids, the finding is the latest evidence suggesting that Neanderthals may not have been as different from modern humans as some researchers have thought.
The study by Debbie Guatelli-Steinberg, assistant professor of anthropology at Ohio State , appeared in the current 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 Clark Larsen, professor and chair of anthropology, both at Ohio State , were co-authors in the study.
“Based on our study of the enamel of these Neanderthal teeth and other modern ones, we can’t support the claim that Neanderthals grew up more quickly than do modern humans,” she said.
Key to this conclusion are microscopic lines on the outside of teeth that mark the incremental growth of enamel on a young tooth. Like tree rings that can gauge the age of a redwood, these striations – called perikymata – record new growth on the surface of the tooth.
Researchers know from earlier work that these markings are present in all forming teeth, signifying six to 12 days of growth. By multiplying that interval by the number of perikymata on a tooth’s surface, researchers can gauge how long it took for the tooth to mature. And that gives them an indication of the length of an individual’s childhood.
Neanderthals, Homo neanderthalensis, were the dominant hominid inhabiting most of what is now Europe and western Asia . Remains have been found as far south as Iraq and as far north as Great Britain . Fossil skulls reveal the distinctively prominent brows and missing chins that set them apart from later humans.
They thrived from about 150,000 to 30,000 years ago until their lineage failed for as-yet unknown reasons. Most researchers have argued that their life in extremely harsh, Ice Age-like environments, coupled with their limited technological skills, ultimately led to their demise.
In a study published last year in the journal Nature, other researchers contended that Neanderthal teeth took 15 percent less time to reach maturity than those in later Homo sapiens, suggesting to them that a Neanderthal childhood would be shorter than our own.
But Guatelli-Steinberg’s team wanted a broader comparison and therefore compared the teeth from Neanderthals to those of three modern populations – people currently living in Newcastle-upon-Tyne , U.K. ; indigenous people from southern Africa, and Inuit from Alaska dating from 500 B.C. until the present.
“We chose these three groups since they would provide a good cross-section of various populations from different regions of the world,” she said. “We feel that they give us some insights into the variation that exists within modern humans.”
For the study, the researchers used precise dental impressions Guatelli-Steinberg and Larsen made of 55 teeth believed to come from 30 Neanderthal individuals. These were compared to 65 teeth from 17 Inuit, 134 teeth from 114 southern Africans and 115 teeth from as many Newcastle residents. In all cases, the researchers tallied the number of perikymata on the enamel surface of the teeth.
Guatelli-Steinberg said that the results showed that the enamel formation times for the Neanderthals fell easily within the range of time shown by teeth from the three modern populations – a conclusion that did not support a shorter childhood for the Neanderthals.
Enticing though it may be, these new findings haven’t convinced the researchers that a Neanderthal childhood was equal to a modern human’s.
“The missing key bit of data to show that would be evidence for when the first molar tooth erupted in the Neanderthals, and we simple have no evidence of when that occurred,” she said.
The length of time is important, the researchers say, because unlike all other primates, humans have an extended period of childhood growth, during which brain matures both in size and through experiences. Some earlier hominids matured far more quickly than modern humans.
“The question is when exactly did that pattern of development evolve in the growth of humans,” she said.
Support for this research came from a grant from the Leakey Foundation and from the College of Social and Behavioral Sciences at Ohio State .
However, this is contradicted by a later study
Neanderthal Children Grew Up Fast
ScienceDaily (Dec. 5, 2007) — An international European research collaboration led by scientists at the Max Planck Institute for Evolutionary Anthropology reports evidence for a rapid developmental pattern in a 100,000 year old Belgian Neanderthal (Homo neanderthalensis).
A new report details how the team used growth lines both inside and on the surfaces of the child’s teeth to reconstruct tooth formation time and its’ age at death.
Scientists found differences in the duration of tooth growth in the Neanderthal when compared to modern humans, with the former showing shorter times in most cases. This faster growth resulted in a more advanced pattern of dental development than in fossil and living members of our own species (Homo sapiens).
The Scladina juvenile, which appears to be developmentally similar to a 10-12 year old human, was estimated to be in fact about 8 years old at death. This pattern of development appears to be intermediate between early members of our genus (e.g., Homo erectus) and living people, suggesting that the characteristically slow development and long childhood is a recent condition unique to our own species.
Neanderthal life history, or the timing of developmental and reproductive events, has been under great debate during the past few decades. Across primates, tooth development, specifically the age of molar eruption, is related to other developmental landmarks such as weaning and first reproduction.
Scientists have previously found evidence to both support and refute the idea that Neanderthals grew up differently than our own species. In this new study, researchers used information from the inside of a molar tooth, coupled with data from micro-computed tomography (micro-CT), as well as evidence of developmental stress on the outsides of tooth crowns and roots.
This yields the first chronology, or time sequence, for Neanderthal tooth growth, which differs from living humans. The Scladina Neanderthal grew teeth over a shorter period of time, and has more teeth erupted (present in the mouth), than similarly-aged fossil or living humans (Homo sapiens).
This suggests that other aspects of physical development were likely more rapidly achieved as well, implying significant differences in the behaviour or social organization of these ancient humans.
Journal reference: Tanya M. Smith, Michel Toussaint, Donald J. Reid, Anthony J. Olejniczak, Jean-Jacques Hublin, Rapid Dental Development in a Middle Paleolithic Belgian Neanderthal, Proceedings of the National Academy of Sciences USA December 2007
Another news item noted grooves in the teeth that seem to have been caused by cleaning their teeth with sharp little sticks
– Two molar teeth of around 63,400 years old show that Neanderthal predecessors of humans may have been dental hygiene fans, the Web site of newspaper El Pais reported on Tuesday.
The teeth have “grooves formed by the passage of a pointed object, which confirms the use of a small stick for cleaning the mouth,” Palaeontology Professor Juan Luis Asuarga told reporters, presenting an archaeological find in Madrid.
The fossils, unearthed in Pinilla del Valle, are the first human examples found in the Madrid region in 25 years, the regional government’s culture department said.
Neanderthals were predecessors of modern humans who inhabited much of Europe, North Africa and parts of Asia from about 125,000 to 30,000 years ago.
“There are two (teeth), perfectly preserved, in which the wear and tear of a human of about 30 years old is perceptible,” a government statement said.
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