Evolutionary History shows that human populations most probably were originated in Africa, but the Genographic Project (a joint National Geographic-IBM project), the most extensive study to date to use genetic data from human populations, shows the first steps of man's expansion all over the planet.

The study, previewed by Molecular Biology and Evolution in its October online edition and part of the Genographic Project, shows that modern humans emigrated from Africa through the southern route, through Arabia, rather than the northern route through Egypt. It also shows that our ancestors spread into Eurasia along a route located between Iran and India, and not through the Middle East as scholars had thought.

The study was carried out by Marta Melé, the first author of the work, Marc Pybus, David Comas and Francesc Calafell of the IBE, with genetists from other countries (the USA, the Netherlands, India, Russia and China), and was directed by Jaume Bertranpetit, researcher at the Institute for Evolutionary Biology (UPF-CSIC) who  coordinates the Genographic Project in Europe with David Comas. It also included researchers from the Genographic Project Consortium, as well as a computing team from IBM.

African Populations are the Earth's most diverse

The data from a significant group of human populations provided by research collaborators with the project were analyzed using computational methods and powerful algorithms, in order to rebuild DNA recombinations from the past and to measure the size and the history of ancient populations.

As regards humanity's Great Migration from Africa, analysis of the X-chromosome from 1,000 samples from various geographic areas revealed that  after leaving the Horn of Africa, man crossed Straits of Bab-el Mandeb between Eritrea and Yemen and from there spread to India and Eurasia (see Figure)

The similarities in DNA recombination patterns transmitted in different populations have ledscientists to confirm that African populations are the most diverse on Earth, and that the diversity of lineages outside Africa is a subset of that present on that continent.

The study has enabled calculation of the possible size of ancient human communities. If the initial African population has a value four times greater, human communities around the Old World could have contained a few thousand individuals each.

The application of new analytical methods to DNA recombination diversity studies highlights the strength of the Genographic Project approach. According to Spencer Wells, director of the Genographic Project, "first we focused on achieving a good collection of samples from all over the world and on constructing a good standardized data base. Using this valuable resource, we were able to start to apply new methods of genetic analysis to achieve a better understanding of the migratory history of our species".

New analytical methods to DNA recombination has been applied

Until now, it was believed that it would be impossible to plot the map of DNA's recombination history because of the inherent complexity in the overlapping of the patterns in each generation. Now it has been made possible thanks to a new analytical method that has enabled scientists to infer the recombinations of the past from human DNA. This methodological approach has produced a completely different result from the family tree expected: the graph of recombinations that emerges from it resembles an architecture web rather than a tree with branches.

The innovative analytical method brings to light the recombinations of DNA of chromosomes over time to light. The recombination of genetic material is a way of creating new sequences of genes in subsequent generations. By means of the recombination process, DNA molecules break up and recombine to form new pairs. It is estimated that ninety-nine percent of the human genome that is transmitted to the following generation undergoes this recombination process.

In the study, the authors say "Imagine that a recombining chromosome acts like a pack of cards. When a pair of chromosomes mingle together, they create new DNA combinations that will be transmitted to the future generations. This process is produced thanks to the recombination, from generation to generation, and contributes to genetic diversity in humans and in other species".

Reference Work:

Marta Melé, Asif Javed, Marc Pybus, Pierre Zalloua, Marc Haber, David Comas, Mihai G. Netea, Oleg Balanovsky, Elena Balanovska, Li Jin, Yajun Yang, RM. Pitchappan, G. Arunkumar, Laxmi Parida, Francesc Calafell, Jaume Bertranpetit, and The Genogràfic Consortium (2011), " Recombination gives a new insight in the effective population size and the history of the Old World human populations", Mol Biol Evol (2011), doi:10.1093/molbev/msr213.