But i heard DNA samples can be taken from bones?
Very difficult to do such a thing because fossilized both are often poor quality, and their DNA is contaminated.
Freezing provides the ideal preservation conditions. The most widely accepted oldest DNA yet isolated comes from 400,000-year-old plants found in ice in Siberia. But most specimens are not excavated from such places.
An improved technique for retrieving DNA from fossil bone, just published in the journal Proceedings of the National Academy of Sciences (PNAS), may help.
Dr Michal Salamon, from the Weizmann Institute of Science in Rehovot, Israel, and colleagues, showed that "crystal aggregates", small mineral pockets formed during fossilisation, can preserve DNA better than the rest of the bone.
They compared DNA extracted from these crystal aggregates with genetic material taken from untreated, whole-bone powder. The samples were taken from eight different modern and fossil bones.
They found better preserved, less contaminated DNA could be recovered from the isolated crystals.
This approach, "significantly improves the chances of obtaining authentic ancient DNA sequences, especially from human bones", they told PNAS.
Commenting on the latest research, Dr Michael Hofreiter, from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who helped decode 40,000-year-old nuclear DNA from a cave bear earlier this year, said: "It's possible; but there need to be more studies on more samples, and they need to show that you don't get human contamination of animal bones.