Believe it or not, 3.7 billion people have herpes. Most get it through harmless interactions, like sharing a spoon or kissing a baby, and are entirely unaware. After all, it’s usually dormant, and for most people, it only causes periodic cold sores.
Despite its prevalence, scientists still argue about when herpes first infected humans. Some argue that it followed us as we left Africa, but others propose a more recent origin when cities began to boom. In a new study, scientists sequenced the first four herpes genomes from dead corpses. They concluded that modern strains of the virus date back to the Bronze Age, around the time when — you guessed it — people began kissing.
“Something happened around five thousand years ago that allowed one strain of herpes to overtake all others,” says co-author Christiana Scheib of the University of Cambridge in a press release.
The team screened 3,000 archaeological digs and found evidence for herpes in four. The samples, which they collected from Russia, the U.K. and the Netherlands, ranged from the third to the 17th centuries. That’s older than the previous oldest herpes genome from a New York patient in 1925. They then compiled whole genomes for three of them.
By comparing the three ancient genomes to the known genetic diversity of herpes today, the scientists calibrated an evolutionary clock that described how quickly herpes DNA mutated between the ancient and modern variants. They then used that mutation rate to back-calculate the time of birth for the original herpes infection. They discovered it was 5,000 years ago during the Bronze Age.
The time was ripe for viral spread for two reasons: People moved into dense cities, and they started kissing. Humans of the Bronze Age migrated from Eurasia into Europe, and they flocked into cities, where neighbors could have commonly spread herpes. Additionally, the first known literary evidence for kissing dates to an Indian manuscript from the same period. If lip-locking became commonplace, it might have promoted transmission between romantic partners.
Herpes is a lifelong infection that is normally dormant, but it can rear its ugly head to cause painful cold sores. It’s normally not a huge problem. But the virus can interact with other diseases like HIV and medical interventions like C-sections to have more extreme, sometimes lethal, effects.
At the moment, herpes isn’t curable. To develop more effective treatment options, researchers require a deeper understanding of how herpes adapted to our bodies and how our immune systems fight back. But the disease transmits and evolves sluggishly, so they need ancient samples to understand the viral-immune arms race. The ones reported here could be a good start, but Scheib says in a press release that she hopes to dig all the way to the root of human evolution: “Neanderthal herpes is my next mountain to climb.”