It is suggested that, under the right conditions, DNA can be preserved for up to a million years. These conditions include:
However, ancient DNA does degrade over time and its preservation is dependent on many chance events. Many biological remains degrade and decompose without leaving any trace at all.
Specimens in collections often haven’t been sampled and preserved with genetic analysis in mind.
Even if ancient DNA is preserved in a specimen, it can be of low quality when compared to modern DNA samples:
If the DNA signal is weak the analyses are very sensitive to contamination from DNA originating from modern sources.
This occurred in the early days of ancient DNA research, when DNA was reported to have been analysed from dinosaurs and insects preserved in amber, a hundred million years old or more.
We now know that these results came from contaminating DNA on the specimen or from modern DNA introduced during the extraction stage.
The contamination issue has largely been solved by:
Ancient DNA can be described as any DNA extracted from ancient biological specimens, such as archaeological bones, teeth or other tissue.
Ancient DNA can derive from a wide spectrum of sources, including: