1 00:00:02,040 --> 00:00:06,720 Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain 2 00:00:06,800 --> 00:00:10,479 Speaker 1: stuff luring vogel bomb. Here, consider the humble prairie vole. 3 00:00:11,000 --> 00:00:16,239 Speaker 1: Unlike of species, prairie voles are faithfully monogamous. Their lives 4 00:00:16,239 --> 00:00:19,160 Speaker 1: may be short. They're an easy snack for hawks and snakes, 5 00:00:19,200 --> 00:00:22,200 Speaker 1: but once two prairie voles mate, they are bonded until 6 00:00:22,200 --> 00:00:25,920 Speaker 1: the end. Not so at the prairie voles close genetic cousin, 7 00:00:26,040 --> 00:00:30,479 Speaker 1: the philandering montane vole. Montane voles form weak social bonds 8 00:00:30,520 --> 00:00:33,640 Speaker 1: and prefer the mating strategy of use them and lose them. 9 00:00:33,680 --> 00:00:36,600 Speaker 1: The stark differences in mating behavior between these two voles 10 00:00:36,680 --> 00:00:39,920 Speaker 1: species have made them excellent subjects for decoding the genetic 11 00:00:39,960 --> 00:00:43,760 Speaker 1: roots of sexual monogamy and infidelity. According to a number 12 00:00:43,800 --> 00:00:46,720 Speaker 1: of studies, prairie voles have more receptors in their brains 13 00:00:46,760 --> 00:00:50,040 Speaker 1: for a hormone called vasopressin, which is believed to play 14 00:00:50,080 --> 00:00:52,879 Speaker 1: a key role in pair bonding. Not only do the 15 00:00:52,960 --> 00:00:55,600 Speaker 1: faithful prairie voles have more of these receptors than they're 16 00:00:55,640 --> 00:00:58,480 Speaker 1: cheating cousins, but the receptors are located in a part 17 00:00:58,520 --> 00:01:01,680 Speaker 1: of the brain that's closer to the reward center, so 18 00:01:01,840 --> 00:01:05,600 Speaker 1: When prairie voles mate, their bodies produce vasopressin, which causes 19 00:01:05,640 --> 00:01:08,319 Speaker 1: their brains to reward the vole couple with a flood 20 00:01:08,360 --> 00:01:11,959 Speaker 1: of pleasurable emotions, sealing the social bond. The brains of 21 00:01:12,000 --> 00:01:15,199 Speaker 1: montane voles, on the other hand, have far fewer vasopressin 22 00:01:15,240 --> 00:01:19,000 Speaker 1: receptors and therefore make much weaker connections between pair bonding 23 00:01:19,040 --> 00:01:22,600 Speaker 1: and pleasure. So it's on to the next conquest. The 24 00:01:22,640 --> 00:01:26,400 Speaker 1: location and sensitivity of hormone receptors is dictated by our genes, 25 00:01:26,600 --> 00:01:29,560 Speaker 1: which naturally leads to the question could the urge to 26 00:01:29,640 --> 00:01:32,399 Speaker 1: cheat on our romantic partners be partly a product of 27 00:01:32,400 --> 00:01:35,360 Speaker 1: our genes? Are some of us walking around with prairie 28 00:01:35,440 --> 00:01:38,040 Speaker 1: vole brains while others are stuck with the wandering eye 29 00:01:38,080 --> 00:01:41,160 Speaker 1: of a montane vole. The real stories about the roots 30 00:01:41,160 --> 00:01:44,600 Speaker 1: of infidelity and monogamy are far more complicated than whether 31 00:01:44,640 --> 00:01:47,880 Speaker 1: you have a cheating gene. Human sexual behavior is the 32 00:01:47,880 --> 00:01:52,120 Speaker 1: product of countless influences and interactions, from our early relationships 33 00:01:52,120 --> 00:01:55,800 Speaker 1: with our parents, to social norms around sexuality, to yes 34 00:01:55,920 --> 00:02:00,560 Speaker 1: our genetic predispositions. We spoke with Justin Garcia, and volutionary 35 00:02:00,560 --> 00:02:04,080 Speaker 1: biologist and sex researcher at the pioneering at Kinsey Institute 36 00:02:04,080 --> 00:02:07,720 Speaker 1: at Indiana University. He said, we are never prisoners of 37 00:02:07,720 --> 00:02:10,760 Speaker 1: our biology, but it does explain why some people wake 38 00:02:10,840 --> 00:02:13,880 Speaker 1: up with somewhat different motivations in these areas than other people. 39 00:02:14,600 --> 00:02:18,120 Speaker 1: The influence of these different genetically based motivations is difficult 40 00:02:18,160 --> 00:02:22,359 Speaker 1: to quantify, but study by Australian researcher Brendan z Each 41 00:02:22,520 --> 00:02:26,320 Speaker 1: offers some intriguing clues. Z Each surveyed these sexual habits 42 00:02:26,360 --> 00:02:29,600 Speaker 1: of nearly seven thousand, four hundred twins and siblings in 43 00:02:29,600 --> 00:02:32,519 Speaker 1: Finland and found that nine point eight percent of men 44 00:02:32,800 --> 00:02:35,079 Speaker 1: and six point four percent of women had had more 45 00:02:35,120 --> 00:02:38,040 Speaker 1: than one sexual partner in the past year. But the 46 00:02:38,040 --> 00:02:40,760 Speaker 1: fascinating finding was that these sets of identical twins with 47 00:02:40,840 --> 00:02:45,080 Speaker 1: identical genomes reported the exact same levels of fidelity, while 48 00:02:45,120 --> 00:02:48,960 Speaker 1: fraternal twins and regular siblings did not. That indicates that 49 00:02:49,000 --> 00:02:52,120 Speaker 1: the variations and genes are powerful enough to influence sexual 50 00:02:52,160 --> 00:02:56,519 Speaker 1: behavior beyond other environmental factors. In fact, z Each put 51 00:02:56,520 --> 00:02:59,400 Speaker 1: a number on it. Our genes account for roughly sixty 52 00:03:00,040 --> 00:03:04,800 Speaker 1: infidelity in males and four percent in females. Vasopresident isn't 53 00:03:04,840 --> 00:03:07,400 Speaker 1: the only hormone that's been linked to varying levels of 54 00:03:07,440 --> 00:03:11,919 Speaker 1: monogamy and infidelity. Oxytocin is another hormone released during sex 55 00:03:12,000 --> 00:03:15,400 Speaker 1: and also during childbirth and nursing that strengthens social bonds, 56 00:03:15,600 --> 00:03:18,880 Speaker 1: and female voles with more oxytocin receptors are also more 57 00:03:18,919 --> 00:03:22,720 Speaker 1: likely to mate for life. Garcia at the Kinsey Institute 58 00:03:22,760 --> 00:03:26,440 Speaker 1: conducted a landmark study of dopamine receptors and sexual straying. 59 00:03:26,960 --> 00:03:29,720 Speaker 1: It's long been established that people with fewer or weaker 60 00:03:29,760 --> 00:03:33,840 Speaker 1: dopamine receptors engage in riskier behavior a drug and alcohol abuse, 61 00:03:33,919 --> 00:03:36,680 Speaker 1: and gambling to get the same dopamine rush that the 62 00:03:36,720 --> 00:03:40,360 Speaker 1: average person might get from eating a Snickers. Garcia tested 63 00:03:40,400 --> 00:03:43,160 Speaker 1: a hundred and eighty one participants, some of whom carried 64 00:03:43,200 --> 00:03:46,440 Speaker 1: the weaker DE four variant of the dopamine receptor. He 65 00:03:46,520 --> 00:03:49,120 Speaker 1: found the people with the DE four receptor were fifty 66 00:03:49,560 --> 00:03:53,000 Speaker 1: more likely to report sexual infidelity, and when he looked 67 00:03:53,000 --> 00:03:55,760 Speaker 1: at all participants who cheated in the study, those with 68 00:03:55,880 --> 00:03:58,360 Speaker 1: the defour receptor were far more likely to do it 69 00:03:58,480 --> 00:04:02,160 Speaker 1: multiple times. For Garcia, the genetic evidence points to a 70 00:04:02,240 --> 00:04:05,240 Speaker 1: more nuanced understanding of what it means when somebody cheats. 71 00:04:05,240 --> 00:04:08,880 Speaker 1: In a relationship. He said, the classic explanation is that 72 00:04:08,880 --> 00:04:11,800 Speaker 1: they're not really in love, but maybe they're more motivated 73 00:04:11,800 --> 00:04:20,920 Speaker 1: by other feelings of sensation, risk, and novelty. Today's episode 74 00:04:20,920 --> 00:04:23,400 Speaker 1: was written by Dave Ruse and produced by Tyler Clang. 75 00:04:23,680 --> 00:04:26,440 Speaker 1: For more on this and lots of other sensational topics, 76 00:04:26,560 --> 00:04:40,400 Speaker 1: visit our home planet, how Stuff Works dot com.