Viruses adapt quickly to new conditions, which is accompanied by a change in their genome. This also applies to a special group of viruses, the bacteriophages. A research team from Poland, the Netherlands and Germany has now successfully reconstructed numerous old phage genomes. These include a genome that is around 1,300 years old and is very similar to the modern Mushuvirus mushu, which infects intestinal bacteria. This contradicts the widespread assumption of a ubiquitous high mutation rate in viruses and thus expands our understanding of their evolution. The researchers have published their findings in the journal “Nature Communications”.