Kissing

Tucked away at the back of the BMJ for 13th Feb 2010, I discover this:

Kissing as an evolutionary adaptation is another curious proposition ... the hypothesis suggests that through mouth to mouth sexual kissing, women control when they are exposed to their partner's diseases -- thus, if the woman becomes pregnant, her fetus could avoid primary infection with teratogenic diseases such as human cytomegalovirus during vulnerable periods of developmnent. As this protection would only be conferred if women also avoid contact with other men, viral tetratogens could also be a pressure towards the development of monogamy. [p.372].

An interesting idea. There is something intimate about full-mouth kissing that isn't necessarily true even of full sex, of course. I like the idea that the risk of disease might even be the point of it.