To be fair, we may have given them diseases that ultimately led to their extinction.
Human papillomavirus — also known as HPV — can be a sly little invader.
Though it doesn’t stick around long in most people, some strains of the tiny pollen-shaped virus burrow into the skin and mucous membranes and can cause genital warts and cancer. In the cases where it persists, the virus can live in the body for years, and silently spread to other people through unprotected sex.
New evidence suggests Neanderthals or Denisovans (another extinct near-human) may be to blame for introducing this disease — specially a cancer-causing variant called HPV 16 — to humans. That means, yes, humans had sex with Neanderthals and Denisovans. And, yes, they may have given us their genital warts. Gee, thanks.
That’s the conclusion of a new paper in journal Molecular Biology and Evolution. “When modern humans [i.e., our ancestors] encountered and interbred with Neanderthals/Denisovans in Europe and Asia, a transfer of sexually transmitted pathogens occurred,” the report concludes.
The evidence here is inferred: There are no actual samples of HPV on human and Neanderthal fossils to compare. (HPV does not infect bones.) Instead, the trio of scientists used DNA and math.
DNA contains the instructions for life, but it is also a historical volume. Whether it’s in humans or in viruses, all gene pools regularly accumulate mutations in a predictable manner. By analyzing strains of HPV around the globe and the “texts” encoded in the DNA, they can work backward to trace the virus’s evolution. They can then compare the path of the virus with the path of human evolution. Sometimes the two stories match up nicely.
Here’s the story about HPV emerging from the DNA evidence: The Neanderthal (or Denisovan) ancestors left Africa long before humans did — perhaps hundreds of thousands of years earlier. When they left Africa, both the Neanderthal ancestors and our human ancestors had been exposed to a similar HPV virus ancestor.
The Neanderthals lived in Europe, and the HPV strain they took out of Africa evolved alongside them, evolving into the ancestor of the HPV 16 virus that still causes cancer today.
When humans ventured out of Africa around 60,000 years ago, they encountered Neanderthals and their HPV. They had sex, and then acquired the HPV 16 variant. These results make sense considering that there’s relatively little of this particular HPV 16 strain in sub-Saharan Africa today.
Well, for the sake of public health today, it may not. The vaccines we now have to protect against HPV are effective regardless of the fact that the most dangerous strains of the virus came from extinct near-human relatives.
But it does tell us a lot more about human history, and can give us insight on how exposure to disease has shaped human evolution. After all “the history of humans is also the history of the viruses we carry and we inherit,” as Ignacio Bravo, one of the paper’s co-authors, told Laboratory Equipment, a scientific trade magazine. STDs have been around since the dawn of humanity. Herpes may have first infected our ancestors more than a million years ago. Syphilis has been around since at least the Middle Ages. It’s possible STDs are what encouraged humans to stick to monogamous pairings.
It also gives us some clues about what happened to Neanderthals. If we contracted HPV from them, what did they get from us? It’s possible that humans spread diseases that brought about their extinction. In April, researchers at Cambridge and Oxford Brookes universities published a paper that suggested Neanderthals may have been particularly susceptible to germs that cause stomach ulcers and herpes.
The HPV we got in return is a nuisance, but not a threat to our existence. Today, HPV is responsible for nearly all cases of cervical cancer, and can also cause cancer in the throat and anus. And HPV is everywhere. The Centers for Disease Control and Prevention finds that between 80 and 90 percent of sexually active men and women will be exposed to some form of HPV in their lives (though not all strains cause cancer). In all, HPV is thought to cause around 30,000 cases of cancer a year.
Genetics is helping us fill in the long-forgotten gaps of human history. Remember this: The humans who had sex with Neanderthals were real people. And their genital warts and cervical cancers were just as real and devastating as they can be to us today.
The results mean that humans have been living with this STDs for a long time. And it’s a notable chapter in our human history.
