Getting useful genetic information from ancient specimens requires solving both problems simultaneously.

You must recover enough genuine ancient DNA to be informative, while distinguishing it from the contaminating modern DNA that will inevitably be present.

This is technically extremely demanding work.

Several developments transformed what was possible.

The development of high-throughput sequencing technology — sometimes called next-generation sequencing — made it possible to sequence millions of DNA fragments in parallel, rather than laboriously reading sequences one at a time.

This meant that even highly degraded ancient samples, where the authentic ancient sequences are fragmented and mixed with contaminants, could yield useful information: by sequencing deeply enough, researchers could find the ancient signal in the noise.