The DNA was fragmented — broken into short pieces, as ancient DNA always is — and chemically damaged, with the specific patterns of deamination (a chemical alteration that affects cytosine bases) that are characteristic of authentic ancient DNA and that laboratory methods are specifically designed to detect and accommodate.

The research team that conducted the genome analysis worked at the Centre for GeoGenetics at the University of Copenhagen, the same institution associated with Eske Willerslev and his colleagues who had been central to several other landmark ancient American DNA studies.

The analysis used the next-generation sequencing methods that had transformed the field over the preceding decade, combined with the sophisticated computational approaches for filtering contamination, correcting for damage patterns, and assembling coherent genomic sequences from millions of short, degraded fragments.

The genome they obtained from USR1 was not perfect.