Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain
Speaker 1: stuff luring vogel bomb. Here, consider the humble prairie vole.
Speaker 1: Unlike of species, prairie voles are faithfully monogamous. Their lives
Speaker 1: may be short. They're an easy snack for hawks and snakes,
Speaker 1: but once two prairie voles mate, they are bonded until
Speaker 1: the end. Not so at the prairie voles close genetic cousin,
Speaker 1: the philandering montane vole. Montane voles form weak social bonds
Speaker 1: and prefer the mating strategy of use them and lose them.
Speaker 1: The stark differences in mating behavior between these two voles
Speaker 1: species have made them excellent subjects for decoding the genetic
Speaker 1: roots of sexual monogamy and infidelity. According to a number
Speaker 1: of studies, prairie voles have more receptors in their brains
Speaker 1: for a hormone called vasopressin, which is believed to play
Speaker 1: a key role in pair bonding. Not only do the
Speaker 1: faithful prairie voles have more of these receptors than they're
Speaker 1: cheating cousins, but the receptors are located in a part
Speaker 1: of the brain that's closer to the reward center, so
Speaker 1: When prairie voles mate, their bodies produce vasopressin, which causes
Speaker 1: their brains to reward the vole couple with a flood
Speaker 1: of pleasurable emotions, sealing the social bond. The brains of
Speaker 1: montane voles, on the other hand, have far fewer vasopressin
Speaker 1: receptors and therefore make much weaker connections between pair bonding
Speaker 1: and pleasure. So it's on to the next conquest. The
Speaker 1: location and sensitivity of hormone receptors is dictated by our genes,
Speaker 1: which naturally leads to the question could the urge to
Speaker 1: cheat on our romantic partners be partly a product of
Speaker 1: our genes? Are some of us walking around with prairie
Speaker 1: vole brains while others are stuck with the wandering eye
Speaker 1: of a montane vole. The real stories about the roots
Speaker 1: of infidelity and monogamy are far more complicated than whether
Speaker 1: you have a cheating gene. Human sexual behavior is the
Speaker 1: product of countless influences and interactions, from our early relationships
Speaker 1: with our parents, to social norms around sexuality, to yes
Speaker 1: our genetic predispositions. We spoke with Justin Garcia, and volutionary
Speaker 1: biologist and sex researcher at the pioneering at Kinsey Institute
Speaker 1: at Indiana University. He said, we are never prisoners of
Speaker 1: our biology, but it does explain why some people wake
Speaker 1: up with somewhat different motivations in these areas than other people.
Speaker 1: The influence of these different genetically based motivations is difficult
Speaker 1: to quantify, but study by Australian researcher Brendan z Each
Speaker 1: offers some intriguing clues. Z Each surveyed these sexual habits
Speaker 1: of nearly seven thousand, four hundred twins and siblings in
Speaker 1: Finland and found that nine point eight percent of men
Speaker 1: and six point four percent of women had had more
Speaker 1: than one sexual partner in the past year. But the
Speaker 1: fascinating finding was that these sets of identical twins with
Speaker 1: identical genomes reported the exact same levels of fidelity, while
Speaker 1: fraternal twins and regular siblings did not. That indicates that
Speaker 1: the variations and genes are powerful enough to influence sexual
Speaker 1: behavior beyond other environmental factors. In fact, z Each put
Speaker 1: a number on it. Our genes account for roughly sixty
Speaker 1: infidelity in males and four percent in females. Vasopresident isn't
Speaker 1: the only hormone that's been linked to varying levels of
Speaker 1: monogamy and infidelity. Oxytocin is another hormone released during sex
Speaker 1: and also during childbirth and nursing that strengthens social bonds,
Speaker 1: and female voles with more oxytocin receptors are also more
Speaker 1: likely to mate for life. Garcia at the Kinsey Institute
Speaker 1: conducted a landmark study of dopamine receptors and sexual straying.
Speaker 1: It's long been established that people with fewer or weaker
Speaker 1: dopamine receptors engage in riskier behavior a drug and alcohol abuse,
Speaker 1: and gambling to get the same dopamine rush that the
Speaker 1: average person might get from eating a Snickers. Garcia tested
Speaker 1: a hundred and eighty one participants, some of whom carried
Speaker 1: the weaker DE four variant of the dopamine receptor. He
Speaker 1: found the people with the DE four receptor were fifty
Speaker 1: more likely to report sexual infidelity, and when he looked
Speaker 1: at all participants who cheated in the study, those with
Speaker 1: the defour receptor were far more likely to do it
Speaker 1: multiple times. For Garcia, the genetic evidence points to a
Speaker 1: more nuanced understanding of what it means when somebody cheats.
Speaker 1: In a relationship. He said, the classic explanation is that
Speaker 1: they're not really in love, but maybe they're more motivated
Speaker 1: by other feelings of sensation, risk, and novelty. Today's episode
Speaker 1: was written by Dave Ruse and produced by Tyler Clang.
Speaker 1: For more on this and lots of other sensational topics,
Speaker 1: visit our home planet, how Stuff Works dot com.