One of the legends of St. Valentine says that he was a priest arrested by Roman Emperor Claudius II for secretly performing marriages. Claudius wanted to enlarge his army and believed that married men did not make good soldiers, rather like Halsted’s feelings about surgical residents. But Valentine’s Day is about love, and if you remember a romantic gut feeling when you met your significant other, it might have a physiological basis.
As far as humans are concerned, you may think you know all about sexual signals, but you’d be surprised by new findings. It’s been known since the 1990s that heterosexual women living together synchronize their menstrual cycles because of pheromones, but when a study of lesbians showed that they do not synchronize, the researchers suspected that semen played a role. In fact, they found ingredients in semen that include mood enhancers like estrone, cortisol, prolactin, oxytocin, and serotonin; a sleep enhancer, melatonin; and of course, sperm, which makes up only 1%-5%. Delivering these compounds into the richly vascularized vagina also turns out to have major salutary effects for the recipient. Female college students having unprotected sex were significantly less depressed than were those whose partners used condoms (Arch. Sex. Behav. 2002;31:289-93). Their better moods were not just a feature of promiscuity, because women using condoms were just as depressed as those practicing total abstinence. The benefits of semen contact also were seen in fewer suicide attempts and better performance on cognition tests.
So there’s a deeper bond between men and women than St. Valentine would have suspected, and now we know there’s a better gift for that day than chocolates.
I agree that it’s the science more than the sex that is problematic, but the science does seem heterosexist. If this hypothesis were true, we’d expect to see very low rates of depression among gay men who have regular unprotected sex. Yet this does not appear to be the case.