The message here is: trust your instincts — except that there is an alarming exception. For women taking hormone contraceptives, the reverse is true: they prefer men whose MHC genes are similar to their own. Thus, women on the pill risk choosing a mate who is not genetically suitable (best to smell him first and go on the pill afterwards).
Once again, we see that birth control can have harmful, unexpected consequences.
Having sex can also complicate the way you perceive a potential partner. After sex, the brain releases oxytocin, which results in the warm, companionable feeling of love and the creation of the social bonds that facilitate co-operative child-rearing. Watch out: sex on a whim can lead to feelings of love for a person who is entirely wrong for you.
It's funny how it seems that modern scientists spend time and effort on proving what is common sense: people bond with sexual partners, even those who they think are meaningless. They may have been meaningless at the beginning of the night, but they aren't come morning. Premartial sex can lead to unfortuante choices in marriage. (I think divorce is 3 times as likely for couples who engaged in premarital sex than those who didn't. Neither is a guarantee, but the odds of a successful marriage are higher with abstinence before marriage.)
The more science researches, the more it defends traditional Christian morality; premarital sex is harmful to happiness and is contraception.
Link via Dappled Things