Use mitochondrial DNA to identify ancient samples.When a creature has spent years in the back of a cave, "it basically is nutrients for all the microbes and worms in the environment," says Edward Rubin, director of the US Department of Energy's Joint Genome Institute in Walnut Creek, Calif. With few intact cells remaining, the chances of finding nuclear DNA extraction are slim. However, there are a few thousand copies of the same mitochondria per cell, so aim for mitochondrial DNA instead. Refocusing your efforts on mitochondria also works for especially degraded samples.

Keep samples on ice, and use as soon as possible.The rate of DNA extraction from Neanderthal bones barely exceeds 1%—2% of the genetic sequence, whereas the rate from wooly mammoths can be as much as 60%—80%. This happens because mammoths lived in colder climates...

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