- Aug 24, 2002
Searching for evidence that Africa is the cradle of modern humans, scientists have found that no region in the world has a larger genetic diversity than East Africa and Ethiopia. Except from being a good omen for public health in the region, the evidence points to that the region indeed has the world's longest human population history.
In a letter published in the latest issue of the scientific journal 'Current Biology', three researchers announced this important evidence on how modern mankind spread to colonise the entire globe. The three, Franck Prugnolle, Andrea Manica and François Balloux, had been studying the diversity of human genetic material from several world regions.
A leading theory for the origin of modern humans, the so-called "recent African origin" model, postulates that the ancestors of all modern humans originated in East Africa and that, around 100,000 years ago, some modern humans left the African continent and subsequently colonised the world. They displaced previously established human species such as Neanderthals in Europe and Homo erectus in Asia, without mixing with them, the model holds.
According to the three scientists, this scenario was now supported by "the observation that human populations from Africa are genetically the most diverse and that the genetic diversity of non-African populations is negatively correlated with their genetic differentiation towards populations from Africa."
Their analysis of genetic material had found that "geographic distance from East Africa along ancient colonisation routes is an excellent predictor for the genetic diversity of present human populations, with those farther from Ethiopia being characterised by lower genetic variability."
In other words, one East African is significantly more genetically different from another East African than a European is from another European. Least genetic diversity is found among Native Americans. The double American continent also was the last to be colonised by humans, in line with the evidence presented.
This result had implied that information regarding the geographic coordinates of present populations alone was sufficient for predicting their genetic diversity. "This finding adds compelling evidence for the 'recent African origin' model," the scientists conclude.
Such a relationship between location and genetic diversity was indeed "only compatible with an African origin of modern humans and subsequent spread throughout the world, accompanied by a progressive loss of neutral genetic diversity as new areas were colonised," they further write.
The highlands of East Africa and Ethiopia thus again are cited as the most probable cradle of modern mankind. While Neanderthals were roaming in Europe some 100,000 years ago, the first real modern humans developed in these highlands. Archaeological evidence has suggested the same for several decades.
To the disappointment of the remaining white supremacists, the great genetic diversity in East Africa only can be seen as an asset. The greater the diversity, the lesser chance for genetic mutations. Further, during the exit from Africa and the subsequent colonisation, genetic possibilities were rather lost than gained. Finally, scientists still disagree whether the emigrated colonists mixed with Neanderthals and Homo erectus when reaching their areas of settlement.