Study identifies hominin species that gave our ancestors genital herpes

Monday, 02 October 2017

Cast of a p.boisei skull

Researchers from Oxford Brookes University and the University of Cambridge have identified the species believed to have contracted and passed on genital herpes to early humans.

Two herpes simplex viruses infect primates from unknown evolutionary depths. In modern humans these viruses manifest as cold sores (HSV1) and genital herpes (HSV2).

Unlike HSV1, however, the earliest proto-humans did not take HSV2 with them when our ancient lineage split from chimpanzee precursors around seven million years ago.

Somewhere between three and 1.4 million years ago, HSV2 jumped the species barrier from African apes back into human ancestors – probably through an intermediate hominin species unrelated to humans. Hominin is the zoological ‘tribe’ to which our species belongs. 

Now, a team of scientists from Cambridge and Oxford Brookes believe they may have identified the species: Parathropus boisei, a heavyset bipedal hominin with a smallish brain and dish-like face.

In a study published today in the journal of Virus Evolution, they suggest that P.boisei most likely contracted HSV2 through scavenging ancestral chimp meat where savannah met forest – the infection seeping in via bites or open sores.

Hominins with HSV1 may have been initially protected from HSV2, which also occupied the mouth. That is until HSV2 “adapted to a different mucosal niche". A niche located in the genitals.

Close contact between P.boisei and our ancestor Homo erectus would have been fairly common around sources of water, such as Kenya’s Lake Turkana. This provided the opportunity for HSV2 to pass into our bloodline.

Layering climate data with fossil locations helped us determine the species most likely to come into contact with ancestral chimpanzees in the forests, as well as other hominins at water sources.

Dr Simon Underdown, Senior Lecturer in Biological Anthropology, Oxford Brookes University

The appearance of Homo erectus around two million years ago was accompanied by evidence of hunting and butchery. Once again, consuming “infected material” would have transmitted the virus – only this time it was P.boisei.

Senior author Dr Charlotte Houldcroft, a Virologist from Cambridge’s Department of Archaeology said: “Herpes infect everything from humans to coral, with each species having its own specific set of viruses. For these viruses to jump species barriers they need a lucky genetic mutation combined with significant fluid exchange. In the case of early hominins, this means through consumption or intercourse – or possibly both.

“By modelling the available data, from fossil records to viral genetics, we believe that Parathropus boisei was the species in the right place at the right time to both contract HSV2 from ancestral chimpanzees, and transmit it to our earliest ancestors, probably Homo erectus.”

Dr Houldcroft collaborated with Dr Simon Underdown, Senior Lecturer in Biological Anthropology at Oxford Brookes University to collate data ranging from fossil finds to herpes DNA and ancient African climates. The team generated HSV2 transmission probabilities for the mosaic of hominin species that roamed Africa during “deep time”.  

Dr Simon Underdown said: “Climate fluctuations over millennia caused forests and lakes to expand and contract. Layering climate data with fossil locations helped us determine the species most likely to come into contact with ancestral chimpanzees in the forests, as well as other hominins at water sources.”

Some promising leads turned out to be dead ends. Australopithecus afarensis had the highest probability of proximity to ancestral chimps, but geography also ruled it out of transmitting to human ancestors.

Ultimately, the researchers discovered the key player in all the scenarios with higher probabilities to be Parathropus boisei. A genetic fit virally who was found in the right places to be the herpes intermediary, with Homo erectus – and eventually us – the unfortunate recipients. 

The team believe their methodology can be used to unravel the transmission mysteries of other ancient diseases – such as human pubic lice, also introduced via an intermediate hominin from ancestral gorillas over three million years ago.   

Image: Cast of a P.boisei skull, used for teaching at Cambridge University. Credit: Louise Walsh.