The herpes simplex virus affects us modern humans in two forms — as cold sores (HSV1) and as the more insidious genital herpes (HSV2). But during the early stages of our evolution about 7 million years ago, the branch of hominids that eventually led to Homo sapiens had left behind the HSV2 strain completely.
How, then, did this now-widespread sexually transmitted virus (over one of every six people between the ages of 14 and 49 in the United States has genital herpes, according to the Centers for Disease Control and Prevention) manage to become so prevalent among modern humans? In a paper published Sunday, scientists think the answer lies with an extinct distant ancestor called Paranthropus boisei.
That P. boisei is not even from the genus Homo is enough evidence that this proto-human was not directly a part of the lineage that led to our own species. However, we share almost 99 percent of our DNA with chimpanzees, and P. boisei evolved roughly 2.7 million years ago, long after our ancestors had already split from the branch that went on to evolve into our closest living relatives.
Scientists use the unofficial term hominins to refer to all the early proto-human species and those that followed them following the split from what were at the time ancestors of modern chimpanzees. So, by that classification, P. boisei is, like H. sapiens, a hominin. Hominids, on the other hand, is a collective that refers to all the great apes taken together, which includes us and all other extinct species of the genus Homo, chimpanzees and bonobos, gorillas, and orangutans.
P. boisei walked on two feet, was heavyset and had a brain that was roughly 40 percent the size of a modern human’s brain. The British researchers who published the study suggest in their paper it contracted HSV2 while feasting on meat of chimpanzee ancestors, the infection carrying over either through bites or through open sores on the body.