Saturday, May 21, 2011

Did Modern Humans Evolve in Morocco?

About one hundred kilometres west of Marrakech is a cave in the mountain known as Jebel Irhoud. For anthropologists it is an important site and known for the numerous hominid fossils discovered there. Speculation amongst scientists is that this site is one of the locations in which modern humans first evolved. In a sense, are we all Moroccans?

Currently, the site has yielded seven specimens. The best known of these are portions of two adult skulls, Irhoud 1 and 2, a child’s mandible (Irhoud 3), and a child’s humerus (Irhoud 4). Fossils 1-3 were discovered while the cave was being quarried for barytes and thus their exact context and age has been subject to debate. Originally the Irhoud hominids were considered North African Neanderthals. It is now clear that they are best grouped with other early, anatomically-modern humans.

A new study of the Irhoud 3 mandible was published in 2007 by Tanya Smith, Jean-Jacques Hublin and colleagues. The work shows that this individual was approximately 8 years old at death and showed a stage of development similar to modern European children of the same age. The implications are that this early Homo sapiens showed a modern human pattern of growth and development and likely experienced a similarly prolonged childhood.

Researcher Tanya Smith writes:
Recent developmental studies demonstrate that early fossil hominins possessed shorter growth periods than living humans, implying disparate life histories. Analyses of incremental features in teeth provide an accurate means of assessing the age at death of developing dentitions, facilitating direct comparisons with fossil and modern humans. It is currently unknown when and where the prolonged modern human developmental condition originated.

An application of x-ray synchrotron microtomography reveals that an early Homo sapiens juvenile from Morocco dated at 160,000 years before the present displays an equivalent degree of tooth development to modern European children at the same age. Crown times in the juvenile's macrodont dentition are higher than modern human mean values, whereas root development is accelerated relative to modern humans but is less than living apes and some fossil hominins.

The juvenile from Jebel Irhoud is currently the oldest-known member of Homo with a developmental pattern (degree of eruption, developmental stage, and crown formation time) that is more similar to modern H. sapiens than to earlier members of Homo. This study also underscores the continuing importance of North Africa for understanding the origins of human anatomical and behavioral modernity.

A Jebel Irhoud Skull

Interesting links:

Max Planck Institute for Evolutionary Anthropology

Dienekes' Anthropology

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