Neandertals may have grown up quickly.

A large study of the growth records preserved in fossil Neandertal teeth indicates that these controversial members of the Homo line, despite possessing large brains, grew to adulthood in a surprisingly short time span. Regarded by many scientists as a distinct species that lived from around 130,000 to 28,000 years ago in Europe and the Middle East, Neandertals reached physical maturity by age 15, according to a report in the April 29 Nature.

Neandertals' rapid development supports the theory that they evolved on a genetically separate pathway from Homo sapiens, say Fernando V. Ramirez Rossi of the National Center for Scientific Research in Paris and Jose Maria Bermudez de Castro of the National Museum of Natural Sciences in Madrid.

The researchers used microscopes to inspect the surfaces of 360 fossil teeth, all from the front of the mouth. The teeth came from 119 individuals assigned to one of four Homo species: H. sapiens from between 20,000 and 8,000 years ago, Neandertals, and two species unearthed at Spanish sites--Homo antecessor and Homo heidelbergensis--that date to about 800,000 and 500,000 years ago, respectively.

Tooth enamel grows in layers, each of which accumulates over approximately 9 days. The number and spacing of the horizontal ridges that border each layer enable researchers to calculate the time it took for a tooth to grow.

Of the four species, Neandertals' teeth grew fastest. As suspected, dental development proceeded slowest among prehistoric H. sapiens.

Such rapid tooth growth reflects accelerated body development, which may have evolved because Neandertals typically died at relatively young ages, the researchers theorize.--B.B.