His group has produced landmark studies on a range of topics in human and ecological history: the reconstruction of genomes from permafrost-preserved specimens tens of thousands of years old; the characterization of the first complete ancient human genome from a Pleistocene-era Greenlandic individual; studies of ancient population movements in Europe, Asia, and the Americas; and work on the ancient environmental DNA preserved in permafrost and lake sediments that can reveal ecological histories without requiring the recovery of macroscopic biological material.

The common thread in this diverse body of work is the development and application of methods for recovering genetic information from material that has been partially degraded by time and environmental exposure.

The methodological innovations that make ancient DNA research possible have developed in parallel with the specific scientific questions Willerslev’s group and others in the field have pursued, and the Sitting Bull study represents one application of this methodological toolkit to a historical — rather than archaeological — specimen.

The distinction between historical and archaeological specimens is relevant in the context of the broader ancient DNA research landscape.