These techniques improve with each generation of research. The 2012 Keller genome was produced using the methods and clean-room protocols available at that time. The 2023 reanalysis used improved protocols on new samples taken from the same left iliac bone.
The numbers tell the story of the improvement. The 2012 genome had contamination of approximately 7.5 percent (± 0.25 percent) — meaning roughly one in thirteen sequence reads came from modern human DNA rather than from Ötzi himself. The 2023 genome had contamination of approximately 0.5 percent (± 0.06 percent) — roughly one in two hundred reads. The new genome was produced at 15.33-fold average coverage, approximately double the 2012 figure.
This difference matters because the contaminating DNA was not random noise. It was modern human DNA — DNA from people alive today, or from people who had been in contact with the mummy over the past thirty years of scientific examination. Modern Europeans have a mixture of ancestries that includes Steppe Herder contributions from the Bronze Age expansion. When a small but measurable proportion of the genome reads come from modern human contamination rather than from the ancient individual, they carry that modern ancestry composition with them into the analysis. The apparent Steppe Herder signal in the 2012 genome was, in the 2023 team’s analysis, consistent with contamination at the level documented in that study.
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## Wang et al. 2023: What the Higher-Coverage Genome Found
The 2023 study was led by Ke Wang of the Max Planck Institute for Evolutionary Anthropology, with co-authors including Kay Prüfer, Ben Krause-Kyora, Ainash Childebayeva, Verena J. Schuenemann, Valentina Coia, Frank Maixner, Albert Zink, Stephan Schiffels, and Johannes Krause. The paper appeared in *Cell Genomics* on August 16, 2023, under the title “High-coverage genome of the Tyrolean Iceman reveals unusually high Anatolian farmer ancestry.”