Asking why humans kiss may seem like a silly question to an average person – because it feels good, duh. But an evolutionary biologist wonders why it feels good. Why is kissing a nearly universal human behavior? Dr. Colin Hendrie from University of Leeds has a hypothesis:

They say the gesture allows a bug named Cytomegalovirus, which is dangerous in pregnancy, to be passed from man to woman to give her time to build up protection against it.

The bug is found in saliva and normally causes no problems. But it can be extremely dangerous if caught while pregnant and can kill unborn babies or cause birth defects.

Writing in the journal Medical Hypotheses, researcher Dr Colin Hendrie from the University of Leeds, said: “Female inoculation with a specific male’s cytomegalovirus is most efficiently achieved through mouth-to-mouth contact and saliva exchange, particularly where the flow of saliva is from the male to the typically shorter female.”

Alright, this kind of sounds like a bit of armchair speculation (aka BS) to me, but at least it’s properly labeled a hypothesis. Especially the shorter female part – what? I’m pretty sure all saliva doesn’t gush into the females mouth…of course, I’m a tall female, so maybe I have some biased sampling.

It would be interesting to test levels of certain types of infections depending on how many people an individual has kissed, or something like that. That seems like a study worth participating in! Or at the very least, a good pick up line if you’re trying to snog a biologist – “Hey baby, want to increase your immunity to Cytomegalovirus?”