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Popular Archaeology Research also found evidence of ancient interbreeding between ancestors of modern Africans and another hominin lineage. A genetic study of African hunter-gatherers has revealed important new insights to how human populations of the distant past have evolved to adapt to their environments, a key component of change in human evolution that has led to the genetic diversity we see today in modern human populations. The research, published on July 26th in the journal Cell and led by Sarah Tishkoff of the University of Pennsylvania, involved sequencing whole genomes of 15 individuals, five each from three different hunter-gatherer population groups in Africa. "We sequenced the genomes of five males from each of three African hunter-gatherer populations (Western Pygmy, Hadza, and Sandawe) at high coverage", she said. "We then compared these genome sequences to a previously published genome sequence from a San hunter-gatherer and to publicly available whole-sequence data from other ethnically, linguistically, and geographically diverse African populations.....These genomes were compared to publicly available high-coverage genomes sequenced and analyzed using the same technology and software in a diverse panel of 53 unrelated individuals (including 4 Luhya from Kenya, 4 Maasai from Kenya, 10 Yoruba from Nigeria, and 51 non-Africans), allowing the genomes of African hunter-gatherers to be placed within a global context". [1] The researchers identified more than 13 million variations in DNA sequences in the tested genomes, and more than 3 million of them have not been found in existing databases. "This is the first population genomics analysis using high-coverage whole-genome sequencing," Tishkoff says. "Many of the variants we found would not have been identified without this kind of analysis." Until now, scientists have analyzed only six African genomes that had been sequenced at high coverage, which involves sequencing regions numerous times to achieve high accuracy. Africa is considered to be the ancestral homeland of all modern humans and contains the highest level of genetic diversity among all of the continents. But, says Tishkoff, "even though African populations have played an important role in human evolutionary history, relatively little is known about variation in African genomes". The study has shed more light on the genetic signs of natural selection. As compared to agricultural and pastoral populations, the hunter-gatherer populations showed distinctly different DNA patterns related to immunity, metabolism, smell, and taste, suggesting that the populations adapted to specific pathogens, food sources, and other factors of the local environments they inhabited. In addition, they identified several candidate genes that could be responsible for the short stature of the Western Pygmies, and perhaps, by extension, pygmies in general. The study also revealed evidence of ancient interbreeding between the ancestors of modern Africans and another hominin (possible archaic form of humans)* lineage. "A striking finding in our data set", writes Tishkoff, et. al., "is that compelling evidence exists that extant hunter-gatherer genomes contain introgressed archaic sequences, consistent with previous studies.......In short, we find that low levels of introgression from an unknown archaic population or populations occurred in the three African hunter-gatherer samples examined, consistent with findings of archaic admixture in non-Africans." [1] In other words, just as previous studies have suggested interbreeding between ancenstral modern humans and Neanderthals in Europe, this study shows evidence that the same had occurred between the ancestors of modern Africans and an archaic form of human or other hominin. Exactly what archaic population it might have been is still unknown. The researchers hope that the study will provide an additional foundation for other scientists moving forward with similar genetic research. "Our study has not only vastly increased knowledge about human genomic variation," said Tishkoff, "but also shed light on human evolutionary history and the origins of traits that make each of us unique". [1] Lachance et al., Evolutionary History and Adaptation from High-Coverage Whole-Genome Sequences of Diverse African Hunter-Gatherers, Cell (2012), http://dx.doi.org/10.1016/j.cell.2012.07.009
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