Wednesday, December 21, 2005

Scientists narrow time limits for human, chimp split

A team of researchers has proposed new limits on the time when the most recent common ancestor of humans and their closest ape relatives – the chimpanzees – lived. Scientists at Arizona State University and Penn State University have placed the time of this split between 5 and 7 million years ago – a sharper focus than that given by the previous collection of molecular and fossil studies, which have placed the divergence anywhere from 3 to 13 million years ago.

The scientists analyzed the largest data set yet of genes that code for proteins and also used an improved computational approach that they developed, which takes into account more of the variability – or statistical error – in the data than any other previous study.

Gene studies are needed to address this problem because the interpretation of the earliest fossils of humans at the ape/human boundary are controversial and because almost no fossils of chimpanzees have been discovered.

"No study before has taken into account all of the error involved in estimating time with the molecular-clock method," says Sudhir Kumar, lead author on the report, which was published online in the journal, Proceedings of the National Academy of Sciences. The team describes its new statistical technique as a "multifactor bootstrap-resampling approach."

"There is considerable interest in knowing when we diverged from our closest relative among animal species," says Kumar, who is director of the Center for Evolutionary Functional Genomics in the Biodesign Institute at Arizona State University. "This divergence time also has considerable importance because it is used to establish how fast genes mutate in humans and to date the historical spread of our species around the globe." Kumar was assisted at ASU by research associate Alan Filipski and graduate student Vinod Swarna.


Story here.

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