Genetic evidence for complex speciation of humans and.pdfVIP

doi:10.1038/nature04789 ARTICLES Genetic evidence for complex speciation of humans and chimpanzees 1 1 1 1,2 1,3 Nick Patterson , Daniel J. Richter , Sante Gnerre , Eric S. Lander David Reich The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here we develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human–chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. Our analysis also shows that human–chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently. The genetic divergence between two species (the proportion of largest was about 25 kilobases (kb))5 and suggested that the time nucleotides differing between representative individuals of the two since average genetic divergence of humans and chimpanzee genes is species) can be converted into a divergence time in terms of millions much greater than the time of speciation4,6–8. However, they pro- of years, provided that differences between genomes have accumu- duced inconsistent estima