It has been assumed that the human papillomavirus (HPV) evolved with modern humans, but it looks like the virus' spread can be attributed to an earlier time.
Publishing their findings in Molecular Biology and Evolution, Ville Pimenoff and colleagues have found evidence that HPV16, the HPV strain responsible for most oral and cervical cancers, actually co-diverged with both ancient and modern humans. This challenges the claim that HPV16 underwent evolution alongside modern humans.
"The history of humans is also the history of the viruses we carry and we inherit," said Ignacio Bravo, a co-author for the study.
With up to 5 percent of the human genome featuring Neanderthal DNA, it was evident that early humans got busy. But more than just swapping around genes, hominid "hanky panky" also led to the spread of sexually transmitted infections.
For the study, the researchers reconstructed HPV16's family tree and compared evolutionary histories involving humans and viruses. When they did, they discovered a new pattern that showed that the HPV strain co-diverged with ancient and modern humans but was repopulated later on when contact with Neanderthals began.
More specifically, HPV16's variant A co-diverged with ancient humans while the strain's B/C/D variants co-diverged with modern humans. When these modern humans left Africa and had sexual contact with Denisovans and Neanderthals, they got infected with the HPV16 variant A that had evolved with ancient humans. This allowed the virus to thrive and expand among the modern humans.
Through this scenario, the researchers were able to shed light on a number of questions, like why Africa is the most human-diverse, why HPV16 variant A is virtually non-existent in Sub-Saharan Africa although it is the virus strain's most common variant in the rest of the world, and why HPV16 in general has the largest diversity in East Asia.
According to Bravo, their work hints at the possibility that certain aggressive oncogenic viruses were transmitted when ancient humans had sexual contact with modern humans. Oncogenic viruses are viruses that lead to tumor development.
The researchers are also proposing that the interaction between viral and host genomes may be able to explain why majority of people can be exposed to HPVs but don't get sick, while an unfortunate few experience persistent infections that sometimes develop into cancer.
For their next step, the researchers are looking to trace HPV sequences in the skin remains of ancient humans, which would allow them to test out their hypothesis more directly.
Pimenoff and Bravo were joined by Cristina Mendes de Oliveira for the study. All the researchers are affiliated with the Catalan Institute of Oncology in Barcelona, Spain.
Photo: Erich Ferdinand | Flickr