The fragments also accumulate chemical modifications — specifically a process called cytosine deamination, which converts cytosine bases to uracil bases at damaged sites — that can introduce errors if not properly accounted for in the analysis.

Modern ancient DNA techniques address both problems.

Library preparation methods designed for ancient DNA can work with very short fragments — sometimes just a few dozen base pairs — that would be unusable in standard DNA extraction.

Computational methods can identify and account for the chemical modifications associated with degradation, allowing researchers to distinguish genuine genetic variation from sequencing artifacts caused by those modifications.

The specific technique applied to the Sitting Bull hair sample was particularly focused on recovering autosomal DNA from material where the amount of usable DNA was very small.