By examining the phylogeny of herpes simplex viruses, researchers have uncovered that they've been infecting people for a long time — before people were Homo sapiens.
As the researchers from the University of California, San Diego, report in Molecular Biology and Evolution, they turned to a branch-site random effects likelihood model of molecular evolution to study the two herpes simplex viruses — HSV-1 and HSV-2 — that infect people. From this, they traced HSV-1 to an ancient codivergence event and HSV-2 to a cross-species transmission event that took places some 1.6 million years ago between from the ancestor of modern chimpanzees to an ancestor of modern humans.
"If you think of humans as Homo sapiens proper, then both viruses have been with us since before we were human," UCSD's Joel Wertheim tells the New York Times.