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Primate Study Provides Clues to Chimp, Human Split: Jun 30, 2008

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Lining up genome sequences from different primates gives researchers a peek into the history of these species, when they split off from one another, and how the populations changed. "We were interested in trying to learn about the history of chimpanzees and bonobos, which are our closest living relatives that are not human," says David Reich, a geneticist at Harvard Medical School.

The classical approach to learning about species history using genomic sequences is to amplify a small number of loci and then sequence those, an approach that Reich says is expensive. Instead, he and his lab sequenced nearly 27,000 random reads from a bonobo and 36,000 from an eastern chimpanzee and compared those sequences to central and western chimpanzees, macaque, and human reads from public databases. "We lined up the data that we got from the [bonobos and eastern chimpanzees] with the genome sequences that were in the databases and we saw what we could learn," says Reich.

From this, Reich concludes that bonobos and chimpanzees broke from each other 1.29 million years ago, and then eastern and western chimpanzee parted ways about half a million years ago. The timing of separation of bonobos and chimpanzee also fits with geological data — at about that time, the Congo River formed and may have physically separated the populations.

Surprisingly, Reich also noted that there are regions of chimpanzee and bonobo genomes where they are each more related to humans than to one another. He confirmed the signal the team observed by sequencing amplified SNPs from regions where this incomplete lineage was seen. "The separation of humans and chimpanzees was a complex event, was a long drawn-out speciation, maybe with initial separation followed by a remixing event a long time later," Reich says. And that's something they are interested in pursuing.

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