Monogamy: One is the <i>Only-est</i> Number! :

Let me tell you about my fondness for the work of Helen Fisher, anthropologist and author one of the best books I’ve ever read on the subject of human sexuality, entitled Why We Love.

Dr. Fisher, and her team at Rutgers University, used the latest technology for brain scanning, FMRI (functional magnetic resonance imaging), to record the brain activity of men and women who had just fallen head over heels in love.

Specifically, Dr. Fisher and her team studied the brains of prairie voles, little mice-like critters that, like humans, have a tendency to mate for life -- in fact, the prairie vole is one of only 3 percent of mammals that remain monogamous to their partners. (Hmm, are humans also part of that 3 percent?) Once they’ve selected a mate, prairie voles copulate like mad (over 50 times in two days -- talk about hot and wild) and then set about the business of bonding for life: nesting, mating, protecting and nurturing. Interestingly, a close cousin of the prairie vole, called the montane vole, is only interested in one-night stands and has no desire to be monogamous, even though they are more than 99 percent genetically alike. So what’s the 1 percent difference? What makes the prairie vole so hot and heavy, as well as committed? First of all, during that initial frenzy of copulation, there’s a 50 percent increase in dopamine levels in the reward center of the prairie vole’s brain, along with increases in norepinephrine levels. The montane vole, on the other hand, is without receptors for these potent sex-chemicals.

In humans, dopamine and norepinephrine are considered "natural amphetamines" and play a key role in sexual arousal, as well as goal-attainment. Dopamine not only helps us focus, it also contributes to our choice in mates (that harnessing of raw lust into focused romantic love). When scientists reduced the dopamine levels in the brains of female prairie voles, they were no longer faithful or choosy about sexual partners. In fact, they slutted it up.

Additionally, dopamine also stimulates testosterone. So not only does this natural stimulant engender lust, it also enables us to focus that lust, in the form of sexual preference, on a single person or, in this case, a single prairie vole: "animals express heightened energy, focused attention, euphoria, craving, persistence, possessiveness and affection -- animal attraction. And data suggest that this attraction is associated with two common brain chemicals -- dopamine and norepinepehphrine."

As the Economist wrote in an ode to the faithful little prairie vole, "So long as men can keep their hormones potent/They'll be romantic as that model rodent."

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