Does oral sex help prevent female infidelity?
Oakland University in Rochester, Mich. did a study that surveyed 243 adult men in committed, heterosexual relationships regarding sexual behaviors.
According to the research mate retention appears to be a driving, evolutionary reason behind men's performance of oral sex on women. Making a woman happy through oral sex reduces the likelihood of them going someplace else for sexual relief.
Thus, from an evolutionary perspective, cunnilingus is a tool in a man's arsenal to retain a reliable mate, i.e. make sure the chick he's investing "resources" in won't have some other dude's kid.
There has been some major flaws pointed out against the study. It seems pretty sexist and loaded with double-standards. As a result of its focus on cunnilingus, the study implies that "there needs to be a larger scientific justification for men to perform oral sex on women".