7 NOVEMBER 2008 VOL 322 SCIENCE www.sciencemag.org892CREDIT: RYAN SNOOK; JESSICA NEWFIELD/SCIENCEGenetics of BehaviorNEWSSOME YEARS AGO, A SCIENTIST-EDUCATORtold Science she would never be convinced ofa biological basis for sex differences in mathperformance until someone showed her a“math gene.” The comment rests on a com-monly held misconception: that simple one-to-one links exist between a gene and eachfacet of our personalities. Headlines such as“ ‘Ruthlessness’ Gene Discovered” or “ ‘Divorce Gene’ Linked to RelationshipTroubles” feed that impression.For some of us, it’s satisfying to attributesocial awkwardness to anxiety genes or tothink that the driver who cuts off other carsas he zips across lanes is pumped up by the“warrior” gene. Was it a bad dopaminereceptor gene that made author ErnestHemingway prone to depression? Can varia-tions in a vasopressin receptor gene—a keyto monogamy in voles—help explain adul-terous behavior? But as scientists are discovering, nailingdown the genes that underlie our uniquepersonalities has proven exceedingly diffi-cult. That genes strongly influence how weact is beyond question. Several decades oftwin, family, and adoption studies havedemonstrated that roughly half of the varia-tion in most behavioral traits can be chalkedup to genetics. But identifying the causalchain in single-gene disorders such asHuntington’s disease is child’s play com-pared with the challenges of tracking genescontributing to, say, verbal fluency, out-goingness, or spiritual leanings. In fact,says Wendy Johnson, a psychologist at theUniversity of Edinburgh, U.K., understandinggenetic mechanisms for personality traits“is one of the biggest mysteries facing thebehavioral sciences.”All we really know so far is that behavioralgenes are not solo players; it takes many toorchestrate each trait. Complicating mattersfurther, any single gene may play a role in sev-eral seemingly disparate functions. For exam-ple, the same gene may influence propensitiestoward depression, overeating, and impulsivebehavior, making it difficult to tease outunderlying mechanisms.Each gene comes in a variety of flavors, oralleles, with varying degrees of sequencevariation. One allele might contribute to awinning personality whereas another mayraise the risk of mental illness. Environmentplays a strong hand, bringing out, neutraliz-ing, or even negating a gene’s influence. Andgenes interact with one another in unpre-dictable ways.Science took a look at a few genes thathave been in the news, with an eye towardunderstanding just what we do—and can—know about genes behind individual variationin temperament and personality.Published by AAAS on November 11, 2008 www.sciencemag.orgDownloaded fromLoves me, loves me not …A genetic screen for mari-tal success? It sounds likea Saturday Night Liveskit, but one Canadiancompany is actually offer-ing just that sort of test.For $99, Genesis Biolabsin St. John’s, Newfoundland,will examine your—or yourpartner’s—vasopressin 1a recep-tor (AVPR1a) gene, which this yeargrabbed headlines once as the “ruthless-ness gene” and again as a “divorce gene.” Butis the test really any more predictive thanpulling petals off a daisy?Vasopressin is a hormone involved inattachment to mates and offspring. Amongvoles, prairie voles are true to their mates.Meadow and montane voles prefer to play thefield. Prairie voles have a few extra bases inthe DNA in front of this gene, which influ-ences how much and where vasopressin isreleased in the brain. This difference matters:Extra AVPR1a in the brain makes promiscu-ous meadow voles act more like monogamousprairie voles, spending more time with part-ners and grooming offspring (see p. 900).Subsequent research has disproved anysimple relationship between this gene and ani-mal mating patterns. Nonetheless, scientistshave now observed hints that variation in thehuman AVPR1a gene may influence the farmore complex arena of human behavior.A team led by Hasse Walum of theKarolinska Institute in Stockholm looked atthe DNA preceding the AVPR1a gene inabout 500 pairs of adult same-sex Swedishtwins, all of them married or cohabiting for atleast 5 years, and their partners. One shortvariant of a stretch of DNA in this region—there are several variants—was associatedwith less stable relationships. Answers toquestions such as “How often do you kissyour mate?” and “How often are you and yourpartner involved in common interests outsidethe family?” reflected slightly lower feelingsof attachment on the part of men with thisvariant, researchers reported in the 16 Sep-tember issue of the Proceedings of theNational Academy of Sciences. These menwere less likely to be married and, amongthose in relationships, more likely to haveexperienced recent marital strife.A gene worth testing to be assured of mar-ital bliss? Not quite. “This is a brand-newstudy for which replication has not beenattempted,” Johnson points out.Another paper published last springshowed a differentlink between AVPR1aand how peopletreat others. RichardEbstein and col-leagues at HebrewUniversity in Jeru-salem reported thatthe length of the vari-ant predicted howhuman subjects wouldrespond in the “dictatorgame,” a way to assess altruism.The researchers divided 200 volunteers intogroups “A” and “B.” The “A’s” received $14each and were told to share as much as theywished with a “B” whom they had never met.About 18% kept all the money, and 6% gaveit all away, with the rest somewhere inthe middle. The people who behaved moreselfishly—or, as the headlines proclaimed,more ruthlessly—had the same variant asthe people with the less stable relationshipsin the study mentioned earlier. Ebsteinspeculates that in these people, vasopressinreceptors were distributed in such a waythat they provided less of a sense of rewardfrom the act of giving (or loving). He andother scientists suspect that short variantsof this gene will be implicated in autismand related disorders, because a core fea-ture of autism is the inability to make con-nections with other people.Although such theories are intellectuallyappealing, there are few replicated studiesto give them heft, notes psychologist SimonEasteal of Australian National University inCanberra. Too often, the subjects assessedare too different—How does one com-pare adolescents with marriedcouples?—and the effect ofenvironment too difficult tocontrol for. So,