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## How Hair Preserves What Bone Cannot
One of the less-discussed aspects of the 2023 Beethoven study is its methodological significance for the field of historical genomics.
Hair is not the preferred material for ancient DNA work. Archaeologists and geneticists studying ancient populations typically prefer to work with dense bone material—the petrous bone of the inner ear is particularly valued because it preserves DNA exceptionally well due to its density and low porosity. Tooth dentine is another favored substrate. Hair, by contrast, presents challenges: the hair shaft itself contains relatively little nuclear DNA, the genetic material that carries the full genome, and is more useful for mitochondrial DNA, which is inherited only through the maternal line and exists in far higher copy numbers in each cell.
The 2023 study worked primarily with hair bulbs—the small root structures at the base of the hair shaft that contain cells with nuclear DNA—rather than the hair shaft itself. This required either that the locks contain hair with intact roots, or that methods be developed to maximize the recovery of genetic material from the available material. The Stumpff Lock, which provided the most complete genome coverage of approximately 24-fold, was well-preserved enough to yield useful nuclear DNA at quantities sufficient for whole-genome reconstruction.
The age of the material—hair cut in 1827 and stored for nearly two centuries under various conditions—added complexity. DNA degrades over time, and the rate of degradation depends on storage conditions: temperature, humidity, light exposure, and microbial exposure all affect how much intact genetic material survives. Hair stored in small frames on walls, or in archival boxes without climate control, would experience very different degradation trajectories than hair stored under museum conservation conditions.