Decoding Love - Andrew Trees [76]
Scientists can now offer concrete evidence of the Coolidge effect by monitoring the level of dopamine in animals before and after copulation (dopamine has been dubbed the “molecule of desire” because it is the chemical that motivates us to attain our goals). Take a recent study of rats. When a male rat was shown a new female, his dopamine rose 44 percent, a number that continued to increase before sex but that dropped off drastically after the rat climaxed. The second time he copulated with the same female, the spike in dopamine was smaller, and after several times, the dopamine level hardly rose above normal. If you placed a new female rat on display, though, the male rat’s dopamine rose by 34 percent. In our age of casual sex, all of this has major implications for our relationships, and a strong chemical argument could be made that people looking for long-term partners would be best served by prolonging the period of courtship. Unfortunately, for the swingers among us, it appears that our grandparents’ advice about people not wanting to buy cows when they can get the milk for free has a scientific basis.
Our brains have a funny quirk built into them that enhances this effect. They thrive on a challenge as long as that challenge is not so difficult that it seems impossible. It is the expectation of a reward, rather than the reward itself, that appears to stimulate dopamine production. We all have experienced this at one time or another. Just think back to the last time you deeply longed for something and how achieving that goal proved far less exciting than thinking about it. In fact, even meaningless goals, such as reaching a new level on a video game, can activate our neurons and get our hearts pumping faster. What this means for women is that their best strategy for ratcheting up a man’s level of dopamine and making herself more irresistible is to make sex with her a challenging goal. Once sex occurs, a man’s dopamine level and his desire will inevitably fall off, although a woman can probably maintain it at a higher level if sex does not become a foregone conclusion but something that a man has to earn on a continual basis.
THE SCENT OF ATTRACTION
Of course, once scientists started to consider the chemical basis for love, they realized that what frequently underlies attraction is not strangers in the night exchanging glances but exchanging smells. For a long time, scientists dismissed as preposterous the whole idea that humans could be attracted to one another based on smell. In recent years, though, they have discovered that smell can and often does play a crucial role, which brings me to one of my favorite experiments—the smelly T-shirt test.
It could have been worse. Scientists could have asked us to smell one another’s urine. The first inklings that smell might play a role in human attraction came not from humans but from rats, specifically from a segment of DNA called the major histocompatibility complex or MHC for short, a sequence of more than fifty genes located along a single chromosome that is different for each and every individual. The reason behind this almost infinite diversity is that the MHC acts as a kind of warning system for the body by detecting disease and alerting the body’s defenses to attack, and it has to deal with a bewildering multitude of attackers.
One of the unusual aspects of the MHC is that it is codominant, rather than dominant. With a trait controlled by a dominant gene such as eye color, only the version from one parent will be