A new study out of the University of California, San Diego alleges that genital herpes in humans originated from our ancestors having sex with chimpanzees.

Around two million years ago, early humans like homo erectus sometimes had sex with chimps.

There are two types of herpes: HSV-1 is herpes of the mouth, and HSV-2 is genital herpes. Humans have their own unique version of HSV-1, but not HSV-2, which would have originated in apes.

"Before [modern] humans, there was still cross-species transmission into our evolutionary lineage," the researchers said.

Approximately one in four Americans has genital herpes.

Read more: NBC News

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