Genital warts, or human papillomavirus (HPV), is not just a disease of the modern world and its newfangled sexual mores. In fact, our ancestors were plagued with various strains of HPV long ago homo sapiens evolved. A new study Molecular biology and evolution reveals that when the ancestors of Neanderthals and Denisovans left Africa more than 500,000 years ago, they were already carrying a variant of HPV. The early humans who remained in Africa also had their own variants of HPV. As the two populations evolved, their cancer-causing wart viruses evolved with them — until that fateful moment when homo sapiens and Neanderthal came together, so to speak.
A group of researchers in France and Spain used a common statistical modeling method to trace the evolutionary origin of today’s HPV. By looking at mutated regions in the virus, which occur regularly over time, the researchers found that the origins of HPV date back nearly half a million years. The question was how different strains of HPV (including the extremely carcinogenic HPV16) found their way around the world? Currently, we see almost no HPV16 in Sub-Saharan Africa, while it is incredibly common elsewhere.
The researchers had two working assumptions: either early humans brought HPV from Africa, and new strains developed in populations that split off from each other outside of Africa; or early humans acquired the ancestral strain of HPV16 from Neanderthals and Denisovans they encountered. After modeling the probabilities of several scenarios, the researchers concluded that the latter fit the facts. They write:
The split between Neanderthals/Denisovans and modern human ancestor populations was mirrored by a split in the viral populations, namely HPV16A, carried by ancestral human populations, and HPV16BCD, carried by the populations of modern human ancestors in Africa…Later, the crossing events between Neanderthal and Denisovan populations with modern human ancestor populations lead to a host switch through sexual transmission of the HPV16A virus lineage from archaic populations to the modern human ancestors. The HPV16A lineage thus transferred expanded rapidly in the new host populations and became dominant in Eurasia and the Americas.
In short, when early humans left Africa 60-120,000 years ago, they were already carrying some variants of HPV. Some of those variants were left in African populations and are still around. One variant came with the migrating populations to Eurasia. But HPV16A, the ancestor of today’s dangerous and widespread HPV16, came from Neanderthals and Denisovans. Early humans who had sex with Neanderthals and Denisovans became infected with this variant of genital warts, and over time their unprotected archaic human lineage spread a sexually transmitted infection through most of the world. homo sapiens population.
This lends further credence to the hypothesis that the Pleistocene was full of hominin hanky-panky. The new research also underscores a basic lesson we’ve all learned in the 21st century: Always practice safer sex, even if you get in trouble with a Denisovan.
Molecular biology and evolution2016. DOI: 10.1093/molbev/msw214