Can Mitochondrial Clocks Keep Time?

EVOLUTIONARY BIOLOGYFor more than two decades, biologists have used DNA to peer into the past, to time the divergences of organisms from each other, and to map human migrations. Now a wash of sequence data reveals that in many cases, the main assumption underlying this molecular doesn't hold up: The clock ticks at different rates in different lineages and at different times. This casts into question results ranging from the notion that animals evolved hundreds of millions of years before their first fossils, to mitochondrial Eve, a human female ancestor who lived about 200,000 years ago in Africa. But even as scientists cast a newly critical eye on the clock results, they are proposing and applying sophisticated statistical methods to deal with the clock's idiosyncrasies.