(6 of 7)
A similar kind of imprinting might take place in humans. "Oxytocin release may help us bond to certain features in our partners," says Pfaus. "It's probably part of the mechanism that generates the template of what we find attractive." The next time you see your partner or someone like your partner, he theorizes, "the oxytocin is activated. It doesn't mean you have to be aroused. You just think, God, what a beautiful woman"--which might explain why we're attracted to the same type over and over.
--ATTRACTIVE AROMAS?
Probably the most controversial issue in the chemistry of sexuality is the role of pheromones. In 1971 the University of Chicago's McClintock, then a Wellesley undergraduate, proved scientifically what women in dorms had known for decades: menstrual periods become synchronized when women live together. It's probably because of pheromones, she said--olfactory chemicals that we can detect even though we're not aware of them. In 1998, she did experiments that proved this hypothesis, but, unlike animal pheromones, no human versions have been isolated.
Because menstrual cycles and sexuality are part of an overall system, it's possible that pheromones could trigger desire. Perfumemakers that market pheromone-based scents have latched onto this notion. It's plausible, says Altman, "but I don't think the science is very good on it." Pfaus agrees: "I hope it's true. Totally on faith, I believe it. The problem is that the scientist in me says, 'O.K., but what are these pheromones, and who has shown it?'"
--A DOUBLE SHOT OF LOVE
A newly identified substance that has captured Pfaus's interest is alpha melanocyte polypeptide, also known as melanocyte-stimulating hormone (MSH). In clinical trials, this pituitary hormone had the dual effect of giving men erections and heightening their interest in sex. Pfaus is studying a synthetic version for Palatin Technologies of Cranbury, N.J., which is developing it as a nasal spray. "It's astonishing that you have a little peptide that has such a big, specific effect," he says. It interacts with dopamine, but how, precisely? "We don't know," he says.
Like all substances that promise to increase desire and performance, whether they are prescription drugs or folk aphrodisiacs sold next to the cash register at the quick-stop store, MSH is tough to investigate because of the placebo effect. As Procter & Gamble discovered with its testosterone-patch study, arousal and desire are so entangled with one's state of mind that it's tough to figure out cause and effect. Says Altman: "If you're in a tribal society and taught that something is an aphrodisiac, it probably will be. But someone in Los Angeles taking the same thing probably won't get the same effect."