Sexual infidelity is often associated as a symptom of unhappy and deteriorating relationships. This maladaptive behavior may stem from a history of unstable relationships or having a philandering parent. Alternatively, genetics could be a key player that we could blame for predisposing individuals to cheating.
In the animal kingdom, sexual monogamy in animals is rare due to evolution favoring promiscuity. Males are believed to possess a genetic and evolutionary impulse to seek multiple partners because it increases their chances of producing more offspring. While there is no clear evolutionary advantage for female infidelity, a hypothesis suggests that due to their investment in bearing and nurturing the offspring, they are driven to look for better or more diverse males in pursuit of genetic variability.
Despite substantial evidence linking genetic factors to sexual behavior in pair-bonding animals, there are still many unknowns surrounding the etiology of human sexual infidelity. Vasopressin and oxytocin are among the most studied hormones associated with sexual behavior in mammals and rodents.
Experiments involving vasopressin injections in the brains of monogamous male prairie voles have revealed its role in promoting social bonding while blocking vasopressin signaling inhibits monogamy. Specifically, Arginine Vasopressin receptor 1A (AVPR1A) has been linked to male pair-bonding behavior in voles. Findings in rodent experiments have shown that differences in the promoter regions of the genes for these hormones and their receptors are crucial in behavioral effects. Prairie voles tend to exhibit monogamy, while montane voles are promiscuous. It turns out that the vasopressin receptors in monogamous voles are closer to the ventral pallidum, or reward center, of the brain. Whereas, in the philandering montane voles, the same receptors are found in the amygdala, a center for processing fear and anxiety. Coupling in prairie voles stimulates the reward circuitry and promotes attachment and the formation of lifelong bonds. For bond-eschewing montane voles, sexual activity has minimal impact on attachment; any female vole can be a partner.
Further experiments on rodents involving overexpression of the AVPR1A gene via viral vector transfer in promiscuous male montane species revealed increased partner preferences. In contrast, oxytocin appears to play a significant role in monogamous behavior in females.
We start to question whether a similar mechanism applies to humans. A twin study by Cherkas et al. (2004) tested the genetic linkage between the AVP receptor gene, and infidelity and the number of sexual partners in females. They evaluated that 41% of variation in infidelity and 38% of variation in the number of sexual partners are accounted for by genetic factors; however, statistical tests did not find significant genetic linkage for either behavioral trait. In contrast, Zietsch et al. (2014) have shown that AVPR1A was significantly associated with extra-pair mating in women but not in men. A study by Walum et al. (2008) revealed an association between one AVPR1A polymorphism, called RS3, and traits reflecting pair-bonding behavior in men. In a related yet different measure, Zietsch et al. have displayed that RS3 was not significantly associated with extra-pair bonding in men or women. Furthermore, single nucleotide polymorphism (SNP) candidates of the oxytocin receptor gene (OXTR) also did not show significant associations with extra-pair mating in either sex.
Another gene suspected of being associated with cheating tendencies is the dopamine receptor gene D4 (DRD4), also known as the 'thrill-seeking' gene. Cheating can be pleasurable because it involves a lot of hormonal excitement and a sense of novelty. In a survey conducted by researchers at Binghamton University, State University of New York (SUNY), students were questioned about their sexual activity, and buccal samples were collected for DNA testing. They discovered that those with a long 7-repeat allele of the DRD4 gene reported a higher rate of promiscuity, that is, engaging in one-night stands and being prone to acts of infidelity. However, the researchers also stressed that not all individuals with this certain variant of the DRD4 gene will necessarily exhibit cheating behavior.
The proliferation of sensational studies on the correlation between genes and behavioral patterns ended up with contradictory findings and replicability problems. At this point, we cannot confirm a cause-and-effect relationship between specific genotypes and sexual behavior. Nevertheless, biological factors remain a significant aspect governing our sexual behavior. It is essential to recognize that infidelity is likely influenced by various complex factors, and our behaviors are shaped not just by our genes but also by environmental factors. Ultimately, despite any genetic underpinnings, we always have the ability to exercise our free will and make conscious decisions about our actions.
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