Unlike the oral version of the herpes virus (herpes simplex 1, or HSV-1) — which was passed to humans genetically from ancient chimpanzees during the evolution process — genital herpes (herpes simplex 2, or HSV-2) didn’t make the leap to humankind on its own.
New research suggests that an ancient hominin species (and early human ancestor) called Paranthropus boisei acted as the in-between agent for genital herpes to make the species jump from primates to humans, reports CNN. Bosei stood about four feet tall, had a small brain and wide face. It is most well-known for having big teeth and hefty chewing muscles, the cause for one skull being nicknamed the "Nutcracker Man."
Bosei, ancient chimpanzees, and Homo erectus (modern humans’ most direct ancestor), were all in Africa between 1.4 million and 3 million years ago, in an area where the evolution of modern humans would occur. It would be easy for them to come into contact with each other around water sources, and it was there that bosei most likely acted as the viral transferer between the chimps and Homo erectus.
Researchers theorize that the early humans (Homo erectus) either ate—or had sex with—the ancient HSV-2-carrying bosei, thus passing it into the modern human bloodline. While most viruses cannot be transmitted across different species, chimps and early humans were genetically similar enough for HSV-2 to mutate and adapt to its new host.
“We can ‘blame’ our ancestors for eating other hominins/great apes, this has been the source of other primate-to-human infections such as HIV,” said Charlotte Houldcroft, a virologist at the University of Cambridge Department of Archaeology and senior author of the study that yielded these findings. “Eating other species closely related to oneself has risks, because pathogens adapted to species genetically similar to us will find it easier to jump the species barrier.”
Researchers also say that the amount of worldwide HSV-2 genetic diversity points to an out-of-Africa migration.
“Essentially, when humans migrated out of Africa, they already carried HSV-2, and wherever humans went, their viruses went too,” said Houldcroft. “HSV-2 infects for life and can be passed from mother to baby or between sexual partners, which made sure it successfully spread wherever humans did.”