Ground Report

Two big genetic studies confirm theories that modern humans evolved in Africa and then migrated through Europe and Asia to reach the Pacific and Amercias.The two studies also show that Africans have the most diverse DNA,and the fewest potentially harmful genetic mutations.One of the studies shows European-Americans have more small mutations,while the others show native Americans,Polynesians and others who populated Australia and Oceania have more big genetic changes.The studies,published in the journal Nature on Wednesday,paint a picture of a population of humans migrating off the African continent,and then shrinking at some point because of unknown adversity.Later populations grew and spread from this smaller genetic pool of founder ancestors-a phenomenon known as a bottleneck.Populations that remained in Africa kept their genetic diversity-something seen in many other studies.Bustamante’s team has been looking at the DNA sequences of 15 African-Americans and 20 European-Americans,examining tiny one-letter changes in the DNA code called single-nucleotide polymorphisms or SNPs (pronounced "snips").