After migrating out of Africa, an ancient group of humans circled back through the Levant and moved into northern and eastern Africa, a new research suggests.

An international scientists team reported in the Dec. 15, 2006 issue of the journal Science that this return to Africa occurred 40,000 to 45,000 years ago, around the time that another group left the Levant and peopled Europe.

Modern humans are thought to have dispersed out of Africa along a single southern path, from the horn of Africa across the Red Sea's Bab-el-Mandeb (the Gate of Tears) to the Arabian Gulf and then along the coasts of the Indian Ocean to Southeast Asia and Australasia.

Scientists have divided the worldwide tree of human mitochondrial DNA into branches called "haplogroups," which distinguish human populations from different geographic areas.

Curiously, two haplogroups in northern and eastern Africa, known as M1 and U6, are closely related to other haplogroups found predominantly in Asia, according to Anna Olivieri, the lead author of the report.

Olivieri's team sequenced DNA from a wide range of individuals in the M1 and U6 haplogroups and show that populations bearing these markers must indeed have arisen in southwestern Asia and then returned to northern and eastern Africa some 40,000 to 45,000 years ago.

Changes in climate were fragmenting deserts in these areas around that time, perhaps opening new routes for migration, said the report.

Source: Xinhua