Pääbo himself recognized the contamination problem and spent the following decades developing the rigorous protocols and authentication methods that would eventually make authentic ancient DNA research possible.

The key methodological developments came in waves.

The polymerase chain reaction (PCR), developed in the mid-1980s, allowed the amplification of tiny quantities of DNA into amounts large enough for analysis — an essential tool for working with the sparse genetic material in ancient specimens.

But PCR also amplified contaminating modern DNA with equal efficiency, making the contamination problem more acute rather than solving it.

The shift from PCR-based approaches to high-throughput shotgun sequencing, which occurred in the mid-2000s, was transformative.