Monday, 7 November 2011

The Human Route Out Of Africa Has Finally Been Confirmed

A satellite image of the Bab el Mandab or 'Gates of Grief.
The dotted line is the suggested crossing point by human
Around 70,000 years ago, humans left Africa, mimicking their ancient ancestor Homo erectus and colonising the rest of the world in less than 55,000 years. While the exact route is unclear, genetic, archaeological and fossil evidence have allowed scientists to recreate a very plausible route. There are of course problems with the theory. One of these is how humans actually left the continent of their origin. Palaeoanthropologists have proposed four different routes.

The first two involved sea journeys. One was a crossing at the Straits of Gibraltar while the other used the various islands that dotted the Mediterranean between Africa and Italy. Most dismiss these as unlikely as they required a sea journey of at least 30 kilometres, far further than early modern humans could have attempted. The third is rather interesting. This would have been a journey across the Arabian Desert, and we know that humans tried it.

A collection of human skeletons at the Skhul and Qafzeh Caves proves the theory. Yet the desert formed an impenetrable barrier to the early pioneers. This left one other route: a short sea crossing of just 12 kilometres, possibly less during the dry season, at the Bab el Mandab or Gates of Grief between the Arabian Gulf and the Somalian/Ethiopian/Djiboutian border. Archaeological evidence backs this up and now undeniable, genetic evidence confirms it.

A six year study by the Genographic Project, an organisation created to explore the human genome in relation to the distribution of global populations, used a technique which exploits genetic recombinations patterns to study how human populations diversified and spread. They used the genetic diversity in India as an anchor for the model. If humans had crossed the Arabian Desert, there would be a greater genetic diversity in places like Egypt.

The only explanation for India's abnormal diversity in relation to other geographical zones would be if humans left Africa via the Gates of Grief and spread up through the Arabian Gulf. 'Almost 99% of the genetic make-up of an individual are layers of genetic imprints of the individual's many lineages. Our challenge was whether it was even feasible to tease apart these lineages to understand the commonalities,' said IBM researcher Laxmi Parida.

'Through a determined approach of analytics and mathematical modelling, we undertook the intricate task of reconstructing the genetic history of a population. In doing so, we now have the tools to explore much more of the human genome.' Dr Spencer Wells, director of the Genographic Project, said such methods could provide 'greater insights into the migratory history of our species.' This is an exciting prospect.