Decoding Love - Andrew Trees [81]
YOUR CHEATING . . . GENE
It also appears that there may be a genetic component that determines how likely a man is to cheat, what some researchers have dubbed the “promiscuity gene.” They have found that there is a variant in some genes for the D4 receptor, a dopamine receptor. Because dopamine is the chemical that stimulates us to want things and underlies everything from sexual attraction to gambling addiction, a change in dopamine reception can have a major influence on our behavior. Men with the promiscuity version of the D4 receptor have an increased desire for erotic adventure and have 20 percent more sexual partners than the average man. Researchers estimate that roughly 30 percent of men carry this gene, but before women go on a genetic witch hunt to weed out these philandering miscreants, they should know that, while similar research has not been done on women, it is very likely that some women have a similar genetic variation. Remember—all those children who are not the product of their legal parents’ loins need both a cheating father and a cheating mother.
For a more precise take on a man’s ability—or inability, if you are a glass-half-empty kind of gal—to be faithful, we need to take a look at the rather unprepossessing and very monogamous prairie vole. Upon reaching maturity, the male latches onto virtually the first available female partner. The couple will spend an entire day copulating like, well, voles and then spend the rest of their lives together. Even separation does not change the bond, and when one of the partners dies, the other vole, in a remarkable display of fidelity, does not take a new mate. However, there is another type of mole—the montane vole—which is polygamous.
So, what accounts for the unstinting and admirable monogamy of the prairie vole and the promiscuous polygamy of his montane cousin? It probably all comes down to one small slice of DNA that acts as a blueprint for a particular type of vasopressin receptor in the brain, and the reason that receptor is so important is that the hormone vasopressin, which is released during sex, plays a central role for males in forming monogamous bonds. The prairie voles have this slice of genetic code, which means that they have a lot more vasopressin receptors in their brain than the montane voles. That makes them much more susceptible to the pair-bonding power of vasopressin. When scientists inserted this genetic code into montane voles, they immediately became as monogamous as the prairie voles.
Vasopressin is so powerful that prairie voles don’t even need the sex to form a monogamous bond. They just need the vasopressin. If injected with it, they form a lifelong bond with the first available female, even though they have not had sex. When the vasopressin is blocked, the male vole acts as if he has never seen the female before, even after having repeated sex with her. How many women know that feeling? Vasopressin (and oxytocin for the females) has even been used to create monogamy among polygamous house mice. In a final twist, it turns out that all voles are not created equal when it comes to vasopressin. Further study revealed that some males have a longer version of the gene than others and that those with the longest versions are also the most reliable partners.
So, what sort of vasopressin receptors are men equipped with? The answer is far more complicated than anyone first imagined. Researchers have already found that the human version of the gene comes in at least seventeen different lengths, a number that is likely to grow as more work is done (similar work also needs to be done for women and oxytocin). What this means is that there is a wide spectrum of possibilities when it comes to the issue of how genetically predisposed individual men may be toward monogamy. Still, it may hold the key to understanding long-term bonds between men and women. To give you some idea of how significant this particular gene might be to male behavior, a shorter version of the gene has been found in those