Ancient DNA is almost always degraded and present in very small amounts.

Modern contamination — DNA from the hands, breath, and skin of researchers and technicians — is invariably present in much larger quantities than the ancient DNA of interest.

Distinguishing authentic ancient sequences from modern contamination requires careful analytical procedures and critical evaluation of the results.

The Stone and Stoneking paper on the Hourglass Cave man was conducted with the careful methodology that the field required, including the use of multiple independent extractions to confirm results and the application of controls to detect contamination.

The recovery of a coherent mitochondrial DNA sequence from material approximately 8,800 years old was a significant technical achievement for its time.