Spanish scientists have proposed a new theory that when Neanderthals and Homo sapiens had sex ~60,000 years ago, a particular pathogen, HPV16a was transmitted from Neanderthals to our species. HPV16a is a particular strain of human papillomavirus that is known to cause cancer.
These scientists used a mathematical method to estimate the amount of time that it would have taken for current strains of HPV to develop their current level of diversity via mutation over long periods of time. HPV16, unlike most other strains of HPV is symptomatic, and when studied has a large amount of genetic divergence from other strains. These scientists also evaluated geographic distribution of HPV strains and one of their potential conclusions is that HPV16a was passed from Neanderthals to Homo sapiens after the latter migrated out of Africa.
1. Original paper: Ville N. Pimenoff, Cristina Mendes de Oliveira, and Ignacio G. BravoTransmission Between Archaic and Modern Human Ancestors During the Evolution of the Oncogenic Human Papillomavirus 16
3. Picture: This Human Papilloma virus image was produced using high-dynamic-range imaging (HDRI) from an image taken with transmission electron microscopy. BSIP/UIG via Getty Images