George wrote:

You can get head lice from sleeping in the same place where someone who
has them
last slept. And just because people have slept in the same place, doesn't
mean
that those persons had sex together. The fact is that the DNA doesn't
indicate that there is a close genetic link between the two species.

It's called the "smoking louse", and it is actually H. Sapiens and H.
Erectus that are involved. I didn't get all the details, but the point was
that head lice are _extremely_ specialized parasites. You can catch head
lice from another person a lot more easily than sleeping in the same bed,
but I believe they said that you can't catch head lice from a chimpanzee.

Their theory wasn't that the two species had had sex, just that they had to
have lived in close enough proximity to pass each other the lice, and that
they had to be genetically close enough to share the parasite.
--
derek