Thanks to George Hyde for the link.

Reposted from:
http://www.guardian.co.uk/science/story/0,,2032480,00.html?gusrc=rss&feed=18

Alok Jha, science correspondent
Tuesday March 13, 2007
The Guardian

Modern humans were living in northern Africa far earlier than previously thought, according to scientists. A new analysis of a 160,000-year-old fossilised jawbone from Morocco shows that the homo sapiens in the area had started having long childhoods, one of the hallmarks of humans living today.

It is known that the species homo sapiens emerged in Africa 200,000 years ago, but the oldest fossils that resemble modern humans come from sites in Europe dated to around 20,000 to 30,000 years ago.

The latest find shows that the key time in the development of a complex human society came much earlier than previously thought. The longer people had to learn and develop their brains as children, the more sophisticated their society could become. The new study pushes the date that modern humans emerged back by more than 100,000 years.

"When you look across primates as a whole or mammals you see things that tend to grow fast and reproduce young, they don't tend to be as socially complex as things like great apes and humans," said Tanya Smith of the Max Planck Institute for Evolutionary Anthropology in Leipzig. "That has social implications. You can imagine being parents and having your kids grow up at 10 or 12 versus 16 or 18, it has a lot of implications for your social structure."

By looking at the teeth of a 160,000-year-old human fossil found at Jebel Irhoud in Morocco, she found remarkable similarities to modern humans. "If you were to take a jawbone of an eight-year-old person today and compare it with the relative degree of dental development with this individual from Morocco they would be nearly identical."

She said that the results, published yesterday in the Proceedings of the National Academy of Sciences, were unexpected. "We know that earlier fossil humans show a more rapid period of growth and development. At a given age they show more teeth erupted than a living human today. This is the earliest evidence of something that ... hadn't been detected before in the fossil record older than maybe 20,000 - 30,000 years ago."

Analysing teeth is an established proxy for understanding the development of ancient humans. "In studying the teeth we understand more how growth and development would be characterised in a species and how it's changed through time," said Dr Smith. "There's a strong relationship between when an individual erupts their teeth and how long their childhood is, what age they begin reproducing, how long they live."

She said that as children grow a record of lines is left behind in their teeth, similar to rings in a tree. "These lines are left behind in the dental hard tissues and they persist for millions of years. You can count them and measure them. By knowing their spacing you know the speed of growth, and by knowing their number you know the time."

Chris Stringer, research leader in human origins at the Natural History Museum in London, said that the new study was important because the Jebel Irhoud site was often neglected by palaeontologists. "This paper certainly provides evidence of a pattern of growth like our own, and this is perhaps not surprising, as there is a very modern-looking child's skull from Herto in Ethiopia."

"While I think that the Irhoud material is probably less modern overall than do the authors of this paper, nevertheless these fossils could certainly represent populations ancestral to modern humans, and they show that North Africa may well have played a significant part in our origins."