Infidelity is partly genetic, but it’s far from determined by your DNA. A large twin study of over 1,600 female twin pairs found that 41% of the variation in infidelity is explained by genetic factors. The remaining 59% comes down to individual experiences, relationship dynamics, and personal choices. Genetics load the dice, but they don’t roll them.
What Twin Studies Reveal
Twin studies are the gold standard for separating genetic influence from environmental influence on behavior. By comparing identical twins (who share 100% of their DNA) with fraternal twins (who share about 50%), researchers can estimate how much of a behavior’s variation traces back to genes versus upbringing and life circumstances.
The largest study on this topic, conducted with UK female twin pairs, found that genetic factors accounted for 41% of the variation in infidelity and 38% of the variation in number of sexual partners. Interestingly, the genetic overlap between these two traits was strong, at 47%, meaning many of the same genetic influences that affect partner count also affect likelihood of infidelity. A separate twin study found similar heritability for number of sexual partners in both men and women, suggesting this isn’t a sex-specific effect. One surprising finding: attitudes toward infidelity showed no genetic influence at all. How people feel about cheating is shaped entirely by their environment and personal experiences, even though the behavior itself has a significant genetic component.
The Dopamine Connection
One of the most studied genetic links to infidelity involves a gene called DRD4, which affects how your brain processes dopamine, the neurotransmitter tied to pleasure, reward, and novelty-seeking. This gene comes in different versions, and one variant, the 7-repeat allele (7R+), is present in about 24% of the population.
A study published in PLOS One found that people carrying at least one copy of the 7R+ variant were almost twice as likely to have had a one-night stand: 45% of 7R+ carriers reported casual sex compared to 24% of those without it. Among those who were unfaithful, 7R+ carriers reported more than 50% more outside partners than non-carriers. The pattern is consistent: this gene variant is associated with a stronger pull toward sexual novelty. But it’s worth noting that plenty of 7R+ carriers in the study were perfectly faithful, and many people without the variant were not.
Vasopressin and Pair-Bonding
Another gene of interest is AVPR1A, which controls receptors for vasopressin, a brain chemical involved in social bonding and attachment. Much of what we know about this gene comes from research on voles. Prairie voles, which mate for life, have a very different version of this gene’s regulatory region than their promiscuous cousins, montane voles. When researchers inserted the prairie vole version of the gene into mice, those mice became more socially bonded, behaving more like the monogamous species.
In humans, variations in the AVPR1A gene have been linked to differences in pair-bonding behavior. One variant, known as the 334 allele, is associated with changes in brain activity in regions important for attachment and emotional processing. Men carrying this allele reported lower relationship quality and were less likely to be married. However, the large UK twin study that established the 41% heritability figure found no direct association between AVPR1A and infidelity in women, suggesting the picture is more complicated than a single gene can explain.
Personality Traits as the Middle Step
Genes don’t code for infidelity the way they code for eye color. Instead, they influence personality traits that make certain behaviors more likely. Two traits with strong genetic roots, sensation-seeking and impulsivity, are consistently linked to risky sexual behavior.
Sensation-seekers are drawn to novelty, excitement, and new experiences. Impulsive decision-makers act without much deliberation. Research on a large sample of young adults found that these traits work through different pathways: sensation-seekers are more likely to put themselves in situations where infidelity could happen, while impulsive individuals are more likely to make poor decisions once they’re in those situations. When both traits are present, they can amplify each other, particularly when alcohol or drugs are involved. Since both traits are substantially heritable, they represent one of the key routes through which genes influence infidelity indirectly.
How Environment Shapes Genetic Risk
Genetic predispositions don’t operate in a vacuum. The field of gene-environment interaction studies how life circumstances dial genetic tendencies up or down. In the context of relationships, this research tells a nuanced story.
One study created a genetic composite score across five genes related to serotonin and dopamine function and found that people who scored higher on genetic risk showed more hostile behavior toward romantic partners, but only if they had experienced hostile parenting during adolescence. People with the same genetic profile who grew up with positive parenting showed more positive relationship behavior instead. The genes amplified whatever environment the person grew up in, rather than pushing behavior in one fixed direction.
Relationship quality itself interacts with genetic predispositions. Research on a variation in the serotonin transporter gene found that people with certain versions of this gene were more emotionally reactive to their partners, for better and worse. Negative interactions in their marriages predicted steeper declines in relationship satisfaction over a 13-year follow-up, compared to people with a different version of the gene. Another study found that genetic influences on mental health problems were strongest when marital quality was low, suggesting that a good relationship can buffer against genetic vulnerabilities, while a bad one can activate them.
What This Actually Means
A 41% heritability estimate means that in a population, about two-fifths of the reason some people cheat and others don’t can be traced to genetic differences. It does not mean any individual is 41% destined to be unfaithful. Heritability is a population-level statistic, not a personal forecast. Height is about 80% heritable, yet nutrition still matters enormously for how tall any given person grows.
The genetics of infidelity work through tendencies, not commands. Certain gene variants make a person more responsive to novelty, more impulsive, or less naturally inclined toward deep pair-bonding. But those same traits can be channeled in countless directions. A sensation-seeker might become an unfaithful partner, or they might become a rock climber, an entrepreneur, or a travel photographer. The trait is heritable; what you do with it is not.
Perhaps the most telling finding from the twin research is that attitudes toward infidelity have zero genetic influence. Your moral framework, your beliefs about loyalty, and the standards you hold yourself to are shaped entirely by your environment and your choices. Genes may make temptation louder for some people, but they don’t override the ability to choose how to respond to it.