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Childhood clues to modern human evolution

14 March 2007

Studies on fossil specimens from a 160,000-year-old child reveal more clues to the evolution of modern humans.

Tests on remains from a child show it was growing as slowly as an eight-year-old child would today. This is the earliest evidence of a prolonged childhood in our modern human ancestors, Homo sapiens .

'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,' says Chris Stringer, human origins expert at the Natural History Museum.

Frontal view of cast of adult male Homo sapiens from Jebel Irhoud in Morocco.

Frontal view of cast of adult male Homo sapiens from Jebel Irhoud in Morocco.

Three modern human skulls from Herto in Ethiopia were dated and described  in 2003 and at 160,000 years they are some of the oldest examples of modern humans, Homo sapiens .

'What is also interesting is that in this paper is the first direct date on the material from Irhoud (Morocco), placing it at about the same age as the Herto finds - about 160,000 years old. This allows us to directly compare these samples from people living across North Africa, Morocco and Ethiopia.'

Testing bones and teeth

The team of scientists carried out various tests on the fossilised bones and teeth. They looked for molar teeth in the jaw that may not have erupted, an important clue to the development of a child. And a powerful X-ray technique on a fossilised tooth revealed microscopic growth lines hidden inside. This shows the tooth was immature and had grown slowly, the same as an eight-year-old child's would today.

Long childhoods

Humans have the longest childhood of all primates, and this feature in nature is associated with complex social structures, as the brain has longer to develop during childhood.

More ancient human ancestors grew up much faster. For example Australopithecines , living about 3 million years ago, may have reached adulthood by the age of 12.

Jebel Irhoud site

The fossil remains of this child, who was about eight years old, were discovered in the Jebel Irhoud site in Morocco in 1968. 'This is a very important site and has often been neglected in the discussions of modern human origins,' says Chris. 'In my own case, studies of an adult skull from this site over 30 years ago was one of the factors that led me to the view that our species had evolved in Africa.'

'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,' concludes Chris.

A team from the Max Planck Institute of Evolutionary Anthropology in Germany and the European Synchrotron Radiation Facility in France carried out the research.

The research is published in the Proceedings of the National Academy of Sciences .