Hammer and team studied DNA sequence data from three sub-Saharan African populations: Mandenka, Biaka and San to test models of African archaic admixture.
The Mandenka are an agricultural population from West Africa, while the Biaka and the San are historically isolated hunter-gatherer populations from Central and Southern Africa, respectively.
The team conducted extensive simulations to test the likelihood of gene flow from an archaic population to anatomically modern humans. The simulations rejected the default position, or null hypothesis, that no admixture took place.
The result gave the scientists confidence to infer that contemporary African populations contain a small proportion of genetic material--about 2 percent--that moved from a species of archaic humans into the gene pool of anatomically modern humans about 35 thousand years ago.
They surmise that this archaic population split from the ancestors of anatomically modern humans about 700 thousand years ago.
"We do not have ancient DNA, i.e., from a fossil specimen, to directly compare with DNA from contemporary populations, so our approach was indirect or inferential," said Hammer. But there are several candidates in the African fossil record that may have added their genetic material to modern humans such as Homo heidelbergensis, an extinct species of the genus Homo that lived between 600 and 400 thousand years ago.
"This study represents an approach to answering long-standing questions about the contributions of archaic, extinct forms of our genus to the gene pool of our modern human species," said Carolyn Ehardt,
|Contact: Bobbie Mixon|
National Science Foundation