But they were not applied consistently. They were applied specifically to Bj 581 after the identification of a female occupant. The researchers’ response — that the critics were holding the female interpretation to a higher standard of proof than the male interpretation had ever been required to meet — is a pointed observation about the sociology of knowledge.
It is not, however, a demonstration that the warrior interpretation is correct. It is a demonstration that the skepticism applied to the warrior interpretation has been selectively applied. Whether the interpretation is correct or not depends on the evidence, not on the consistency with which skepticism is deployed.
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## What Ancient DNA Can and Cannot Do
The 2017 Birka study was one of many that emerged in the 2010s as ancient DNA technology transformed archaeology. Understanding what the technology can and cannot do helps calibrate the significance of the specific findings.
Ancient DNA analysis can determine biological sex — with high confidence when multiple samples are available and when contamination can be excluded — because sex is encoded in the chromosomes, and chromosomes are observable in DNA data. The XX finding in Bj 581 is one of the most robustly established facts the study produced.
Ancient DNA can estimate geographic ancestry and population relationships. The mitochondrial haplogroup T2b connects the Bj 581 individual to a lineage found in England, Iceland, and Scandinavia. The nuclear DNA can be compared against reference populations to identify which modern or ancient populations the individual’s ancestry resembles most closely. This kind of analysis comes with significant caveats — ancient populations do not map cleanly onto modern ones, the reference populations available for comparison are incomplete, and population structure in the Viking Age was different from today’s — but it provides information about broad geographic origin that is otherwise unavailable.