Enlarge / It’s all fun and games until Ringo goes Neanderthal on you. (credit: Caveman)

Genital warts, or human papillomavirus (HPV), isn’t just a disease of the modern world and its newfangled sexual mores. In fact, various strains of HPV plagued our ancestors long before Homo sapiens evolved. A new study in Molecular Biology and Evolution reveals that when the ancestors of Neanderthals and Denisovans left Africa over 500,000 years ago, they were already carrying a variant of HPV. The early humans who remained in Africa had their own variants of HPV, too. As the two populations evolved, their cancer-causing wart viruses evolved with them–until that fateful moment when human and Neanderthal came together, as it were.

A group of researchers in France and Spain used a common statistical modeling method to trace the evolutionary origins of today’s HPV. By looking at mutated regions in the virus, which occur regularly over time, the researchers discerned that HPV’s origins go back almost half a million years. The question was, how did various strains of HPV (including the extremely carcinogenic HPV16) make their way around the world?

The researchers had two working assumptions: either early humans brought HPV with them out of Africa, and the different strains evolved in populations that split off from each other outside Africa; or early humans acquired the ancestral strain of HPV16 from Neanderthals and Denisovans they encountered. After modeling the likelihood of different scenarios, the researchers concluded that the latter fit the facts. They write: