Does science really need to give Tiger Woods/Brett Favre an excuse?

"Sorry, sweetheart, I didn't mean to bang anything with a hole and a heart beat that came my way/text that chick pictures of my junk. But you have to forgive me because it's in my DNA. Oh look, it's tee time/game time again."

Add another checkbox to the dopamine receptor gene DRD4 traits - now you can be a politically liberal cheating bastard without blame. A group from Binghamton University led by Justin Garcia
took a look at "sexual behavior, matching choices with genes and has come up with a new theory on what makes humans 'tick' when it comes to sexual activity." The Medical Daily article says:
So, he or she has cheated on you for the umpteenth time and their only excuse is: "I just can't help it." According to researchers at Binghamton University, they may be right. The propensity for infidelity could very well be in their DNA.

"We already know that while many people experience sexual activity, the circumstances, meaning and behavior is different for each person," said Garcia. "Some will experience sex with committed romantic partners, others in uncommitted one-night stands. Many will experience multiple types of sexual relationships, some even occurring at the same time, while others will exchange sex for resources or money. What we didn't know was how we are motivated to engage in one form and not another, particularly when it comes to promiscuity and infidelity."

The biggest culprit seems to be the dopamine receptor D4 polymorphism, or DRD4 gene. Already linked to sensation-seeking behavior such as alcohol use and gambling, DRD4 is known to influence the brain's chemistry and subsequently, an individual's behavior.
I can see promiscuity as a sensation-seeking trait, yes. In the PLoS ONE article, the authors write, "The variable number tandem repeats (VNTR) polymorphism in exon III of the human dopamine D4 receptor gene (DRD4) has been correlated with an array of behavioral phenotypes and may be predicatively responsible for variation in motivating some sexual behaviors, particularly promiscuity and infidelity." Garcia and his team administered an anonymous survey on a detailed history of the sexual behavior and relationships of 181 BU undergraduate students, collected buccal wash samples and genotyped the DRD4 variable number tandem repeats.

The results of the study showed that students with the genetic variation were twice as likely as those without it to engage in sexually promiscuous behavior, according to the BU Pipe Dream article. In addition, 50 percent of those with the gene variation had been unfaithful in a relationship, while only 22 percent of those without the variation had. Garcia said they found that "individuals with a certain variant of the DRD4 gene were more likely to have a history of uncommitted sex, including one-night stands and acts of infidelity. ... The motivation seems to stem from a system of pleasure and reward, which is where the release of dopamine comes in. In cases of uncommitted sex, the risks are high, the rewards substantial and the motivation variable – all elements that ensure a dopamine 'rush.'"

But the data also may show a contradiction - because the DRD4 variation and desire for a dopamine rush can function independently from the desire for a committed relationship, the data suggests that someone can deeply care for their partner and still be unfaithful, the BU article said. Garcia also said that "individuals could be looking for a serious committed long-term relationship, but have a history of one-night stands. At the same time, the data also suggests it is also reasonable that someone could be wildly in love with their partner, commit infidelity, and yet still be deeply attached and care for their partner. It all came back to a DRD4 variation in these individuals."1

In the article Garcia says that the study "doesn't let transgressors off the hook. ... These relationships are associative, which means that not everyone with this genotype will have one-night stands or commit infidelity. Indeed, many people without this genotype still have one-night stands and commit infidelity. The study merely suggests that a much higher proportion of those with this genetic type are likely to engage in these behaviors."
At this point, very little is known about how genetics and neurobiology influence one's sexuality propensities and tendencies but Garcia is hopeful that this study will add to the growing base of knowledge - in particular, how genes might predispose individuals to pursue sensation seeking across all sorts of domains – from substance use to sexuality. This study also provides further support for the notion that the biological foundations for sexual desire may often operate independently from, although absolutely linked to, deep feelings of romantic attachment.
The team is going to look for more genetic markers, as well as - and this is interesting, given the study they just did - look at the receiving end of the infidelity. Garcia has some fascinating research interests, so I'm sure we'll hear more from him on "the evolutionary and biological foundations of human love, intimacy, and sexual behavior." I would love to take his class, "Bioculture of Love" - I get an image of a petri dish filled with junior high school bacteria swimming and tumbling around with pili in each others' back pockets.

An assistant professor of the biological sciences at BU, Anthony Flumera, has the best quote of the article: “I don’t think my wife, also a geneticist here at Binghamton, would accept ‘my genes made me do it’ as an excuse."

1 Where did the commitment gene come in? I missed that one. I assume it's linked with the gene responsible for husbands agreeing to wear matching outfits in family Christmas photos.