July 18, 2007 — Twenty years after it was popularized, the "Out of Africa" theory, which posits that modern humans originally came from Africa before spreading out in a global conquest, has received an emphatic boost, scientists said on Wednesday.

Rival theories about the rise of Homo sapiens sapiens, as anatomically modern man is called, say humans either came from a single point in Africa or among different populations in different parts around the world, who evolved independently from a forebear, Homo erectus.

The "Out of Africa" scenario has been underpinned since 1987 by genetic studies based mainly on the rate of mutations in mitochondrial DNA, a genetic material inherited from the maternal line of ancestry.

The "multiple origins" school, meanwhile, points out that human skulls from around the world have clearly different characteristics, and argues that this proves our species evolved in slightly different forms more or less simultaneously.