Blame it on the gorillas....
New research suggests that humans caught pubic lice or "crabs" from gorillas about 3.3 million years ago. No, not how you're thinking! It was likely from sleeping in gorilla nests or while killing and consuming their meat.
Humans can get two kinds of lice: Pediculus (head lice) or Pthirus (pubic lice). Chimps get Pediculus and gorillas get Pthirus. Though we diverged evolutionary fro our last common ancestors about 7 million years ago, it was not known until this research that early humans and gorillas spent time in the same locations. More info is in the newest issue of BMC Biology.
This info comes at the same time as research that suggests we diverged from chimps only 4 million years ago, not the 6-7 million previously thought.