The second was the development of specific techniques for working with highly degraded ancient DNA — the kind of severely fragmented, chemically damaged material that is all that survives in most archaeological specimens.

Ancient DNA is not preserved intact; it is broken into short fragments by the chemical processes of decomposition, and those fragments carry specific types of damage — particularly the deamination of cytosine molecules — that distinguish genuine ancient sequences from modern contamination.

Learning to identify and filter for these damage patterns made ancient DNA analysis far more reliable.

By the mid-2010s, researchers could routinely sequence complete or near-complete genomes from ancient skeletal material under favorable preservation conditions.

The petrous bone — the densest bone in the human body, located at the base of the skull as part of the temporal bone — had been identified as the most reliable source of ancient DNA, because its density protects the genetic material from the microbial and chemical degradation that destroys DNA in other skeletal elements.