Laboratories could extract and amplify small amounts of DNA from samples a few thousand years old, but the further back in time one went, the more degraded the material and the more likely that what was being amplified was contamination rather than genuine ancient signal.

Samples tens of thousands of years old — like the Anzick child’s bones — seemed, for much of the 1990s and 2000s, to be beyond the practical reach of the technology.

What changed was the development of next-generation sequencing — a fundamentally new approach to reading DNA that abandoned the traditional method of amplifying specific targeted regions and replaced it with the ability to sequence millions of short DNA fragments simultaneously.

This approach was better suited to ancient DNA because it did not require long, intact DNA strands — it could work with the short fragments that were all that ancient samples typically preserved.