News FocusEvolutionary Biology

Can Mitochondrial Clocks Keep Time?

Science  05 Mar 1999:
Vol. 283, Issue 5407, pp. 1435-1438
DOI: 10.1126/science.283.5407.1435

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For more than two decades, biologists have used mitochondrial 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 clock" 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.