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Viruses are widespread infectious agents, but we know little about their origin times due to the general absence of fossil records. The research team of Chuan Ku, Institute of Plant and Microbial Biology, developed a host-calibrated dating method and inferred the evolutionary timescale of giant viruses (Nucleocytoviricota), which cause important diseases (e.g., Mpox, African swine fever) and infect various eukaryotes. The team found that giant viruses are much younger than eukaryotes, originated in an era with significantly higher oxygen levels than before (consistent with their high demand for mitochondria and energy), and spread across all major lineages of eukaryotes through extensive host shifts within the last hundreds of millions of years.

This study was published on February 20, 2025 in Molecular Biology and Evolution, and was funded by Academia Sinica Career Development Award and National Science and Technology Council. The first author is Hwee Sze Tee, a postdoctoral research fellow.