NEANDERTHALS and our human ancestors looked broadly similar, lived at the same time and in the same places. Yet evidence continues to grow that the two kept very much to themselves.
Two studies have added yet more evidence that the two hominids did not interbreed. What鈥檚 more, one of the studies has revealed that Neanderthals鈥� teeth developed much faster than those of their human cousins. This means they may have reached maturity at 15 years old, around three years earlier than our early human forbears.
Some researchers have suggested a close relationship between Neanderthals and early humans, also known as Cro-Magnon man. Both hominids lived in Europe before Neanderthals died out around 30,000 years ago.
Advertisement
Last year, a study of mitochondrial DNA from fossil hominid specimens found Cro-Magnon mtDNA was indistinguishable from samples taken from living people, whereas Neanderthal mtDNA was distinct (New Scientist, 17 May 2003, p 14). Separate research comparing the facial structure of Neanderthals, modern humans and various ape species has also concluded that the differences were too great to allow Neanderthals and humans to be placed within the same species (New Scientist, 31 January, p 15).
Now a study comparing around 150 Neanderthal teeth with those of ancient humans has suggested another difference: our extinct relative matured faster than our forebears (Nature, vol 428, p 936). Primate species that develop slowly also tend to have teeth that take longer to reach maturity, says Jos茅 Maria Bermudez de Castro of the National Museum of Natural Sciences in Madrid, Spain.
He and his colleague Fernando Ramirez Rozzi at the CNRS centre for anthropological sciences in Paris, France, studied growth rings in the enamel of the fossilised teeth. New rings are laid down roughly once every nine days. By counting the number of rings in adult teeth, the researchers calculated that the Neanderthal鈥檚 teeth developed 15 per cent more quickly than those of Cro-Magnon man. From this they inferred that Neanderthals matured around three years earlier.
鈥淚t鈥檚 a very long way to go from more rapid tooth crown formation to significantly earlier maturity,鈥� says Jay Kelly, an expert in tooth development at the University of Illinois in Chicago. But 鈥渋n this one facet of development, Neanderthals and modern humans were clearly on different tracks鈥�, Kelly adds.
The idea that Neanderthals and our forebears did not interbreed has been further bolstered by a genetic study comparing DNA sequences from the mitochondria of fossil Neanderthals and Cro-Magnons. A team led by Svante P盲盲bo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, screened four Neanderthal and five Cro-Magnon fossils for a short sequence of DNA around 30 bases long found in all Neanderthals. They failed to find the sequence in the Cro-Magnon specimens (PLoS Biology, vol 2, p 313).