Mitochondrial DNA appears to mutate much faster than expected, prompting new DNA forensics procedures and raising troubling questions about the dating of evolutionary events. In 1991, Russians exhumed a Siberian grave containing nine skeletons thought to be the remains of the last Russian tsar, Nicholas II, and his family and retinue, who were shot by firing squad in 1918. But two bodies were missing, so no one could be absolutely certain of the identity of the remains. And DNA testing done in

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... 992--expected to settle the issue quickly--instead raised a new mystery. Some of the DNA from the tsar's mitochondria--cellular organelles with their own DNA--didn't quite match that of his living relatives. Forensic experts thought that most people carry only one type of mitochondrial DNA(mtDNA), but the tsar had two: The same site sometimes contained a cytosine and sometimes a thymine. His relatives had only thymine, a mismatch that fueled controversy over the authenticity of the skeletons.