There are a lot of unique things about humans. One of the lesser known facts is that we’re the only primate species infected with two distinct types of the Herpes simplex virus: creatively named HSV-1 and HSV-2. They’re also quite prevalent, with more than 2/3 of the human population being infected with one of the two viruses; which typically cause cold-sores and sometimes other…more icky symptoms. But what’s perhaps more interesting than random facts about Herpes is the history of these two viruses1.
HSV-1 seems to be the “human” variant of the Herpes virus present in all primates that we inherited from our ape ancestors. It evolved and mutated along with us to become a unique virus, endemic to humans. Most other primates seem to have their own such variant (chimps, for example have a variant called called ChV-1). As such this virus has an old history, as old as the human family itself (5 – 7 million years)1.
However, HSV-2 is where things get a bit more interesting. This is much younger, dating to about 1.6 million years ago. As such it predates modern humans, appearing to have developed in Homo erectus. This early human had a body a lot like ours, but a smaller brain. But what’s most interesting is that HSV-2 is most closely related to the chimp strain. In other words, our ancestors were infected by a chimp (or chimp ancestor); and the resulting Herpes virus mutated into a new strain1. Thus giving our species the dubious honor of being the primate with the most types of Herpes.
The family tree of primates (right) and Herpes in primates (right). Note HSV-2 is weird
Although Herpes has a bit of a reputation as an sexually transmitted disease, in actual fact any contact with the bodily fluids of an infected person (or in this case chimp) could pass the disease on. So get your minds out of the gutter; there probably wasn’t any hanky panky going on between our ancestors and chimps. A poor Homo erectus could’ve been suffered a nasty bite from a chimpanzee ancestor and gotten the disease from their saliva2. This is also interesting as it’s perhaps the best evidence that our ancestors and chimps ever interacted.
They’re not the only pathogen to have made such a leap. Genetic analysis of HIV has revealed it is a descendant of SIV (or Simian Immunodeficiency Virus), a similar condition which afflicts primates. Specifically, it seems to be a descendant of a version of SIV present in chimps. This is typically a weaker disease our immune system has no problem eradicating, but it looks like it was rapidly passed from person to person at some point, giving it the chance to mutate into the HIV we all know and love3.
In unrelated news, Dawn of the Planet of the Apes hits cinemas here in the UK soon. It tells the ludicrous story of the human population being decimated by a virus we catch from chimps; allowing the apes to rise to dominance. As I said, it’s a silly idea, clearly without any real-world precedent.
References
- Joel O. Wertheim1, Martin D. Smith, Davey M. Smith, Konrad Scheffler, and Sergei L, Kosakovsky Pond. 2014. Evolutionary Origins of Human Herpes Simplex Viruses 1 and 2. Molecular Biology and Evolution
- Wysocki, edited by Anita L. Nelson, JoAnn Woodward ; foreword by Susan (2006).Sexually transmitted diseases : a practical guide for primary care Totowa, N.J.: Totowa, N.J. p. 50.
- Marx PA, Alcabes PG, Drucker E (2001). “Serial human passage of simian immunodeficiency virus by unsterile injections and the emergence of epidemic human immunodeficiency virus in Africa” Philosophical Transactions of the Royal Society B 356 (1410): 911–20
