Neanderthals grew fast, died young

When you're living on the edge of a largely ice-covered continent, sleeping in caves, sharing turf with giant cave lions and bears, you had better grow up quickly. A new study of teeth shows that Neanderthal children did just that, reaching maturity by about the age of 15.

European anthropologists report today in the journal Nature that Neanderthals seemed to mature faster than both modern humans and also their immediate ancestors in Europe and Asia, based on the enamel growth rates of fossilized front teeth. The technique uses a system similar to tree-ring dating to measure development of the individual.

The early onset of adulthood, which has been suggested by a number of Neanderthal experts in recent years, represents an "evolutionary reversal" within the human family, according to Fernando Ramirez Rozzi of the National Center of Scientific Research in Paris and Jose Bermudez de Castro of the National Museum of Natural Science in Madrid.

Among all other human ancestors right down to modern humans, the trend had been for dental growth to slow with aging, a marker for later overall development and maturity. But among Neanderthals, teeth grew at a fairly constant rate, with other research showing individuals as young as 4 or 5 sporting teeth suitable for the hunting and foraging life.

The authors of the new study argue that Neanderthals, who boasted larger brains than modern humans, must have had a high-calorie diet and a fast metabolism to fuel such rapid growth in a particularly harsh environment.

Neanderthal remains discovered in Europe and the Middle East over the past 150 years point to a young crowd -- clans of 30 to 50 individuals made up mostly of children and juveniles, with women rarely surviving much past 30, and men seldom seeing 40.

Neanderthals roamed the region for about 300,000 years, disappearing from Europe 30,000 years ago, about the same time that modern humans moved in, and the last ice age drew to a close. Scientists continue to debate how much interaction there was between the two groups, and particularly whether they interbred to an extent that the Neanderthals can be considered ancestors to today's Europeans.

Most recent studies, based on DNA analysis and examination of physical traits in fossils, suggest that Neanderthals were not ancestors.

The earlier attainment of adulthood represented "a major developmental shift in relation to other Homo species, and yet again reinforces the fact that Neanderthals were a species distinct from Home sapiens," said Ramirez Rozzi.

This more hurried arrival of adulthood was probably a necessary response to the harsh environment, the researchers and other experts suggest. Women tended to die young while bearing children; men often didn't come back from their hunts. Children had to be ready to fend for themselves at an early age.

While some scientists have argued that more rapid maturity of Neanderthals was a result of starting life with larger brains, Ramirez Rozzi and Bermudez de Castro wrote that "high adult mortality rates are most likely to have driven life-history rescheduling among Neanderthals."

But over the long run, such a short life span, with few grandparents to pass along knowledge of the environment and cultural lore, may have been a negative trait for the Neanderthals, particularly when thrown into competition with modern humans who matured later, lived relatively longer lives, and were able to spend those extra years nurturing and passing along the wisdom of age to their young.

On the Net: www.nature.com

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