Researchers have reconstructed the ancient genomes of herpesviruses from Iron Age and medieval Europeans. They revealed that the HHV-6 virus has been infecting humans for at least 2,500 years. Some people have inherited this virus directly in their DNA and passed it on from generation to generation. The study shows that these viruses co-evolved with humans. One strain of the virus has lost its ability to integrate into human chromosomes. This is the first evidence of this long relationship confirmed by ancient genetic evidence from skeletons.