<p>Nature, Published online: 18 March 2026; <a href="https://www.nature.com/articles/d41586-026-00718-2">doi:10.1038/d41586-026-00718-2</a></p>Genomic analysis has unexpectedly revealed that microorganisms called Asgard archaea, the closest relative of our cellular ancestors, can respire using oxygen. This suggests that the common ancestor of these modern archaea and nucleus-containing eukaryotic cells could have been oxygen-tolerant, contrary to previous models of the origins of complex life.