The Cheat Sheet

Is infidelity written in our DNA

There is no single ‘cheating gene’ sitting on a chromosome like a ticking moral time bomb. What researchers have actually found is a cluster of genetic variants that shape how the brain processes reward, bonding, and satisfaction — and for some people, the emotional arithmetic of monogamy is, neurologically speaking, harder to balance.

At the heart of this is a hormone called vasopressin, which acts as a sort of biological glue for empathy and trust. Researchers have identified a specific variant of the AVPR1A gene where the docks for this hormone — known as receptors — do not function as effectively. For people with this low-binding version, the neurological pull toward a partner after intimacy simply does not stick as firmly. In a 2014 study of over 7,000 twins, women carrying this specific variant were statistically more likely to report extra-pair mating, suggesting that for some, the architecture of attachment is built differently from the ground up.

Vasopressin works in tandem with oxytocin to regulate the neural pathways that reinforce monogamous attachment. While animal studies on prairie voles show that disrupting these receptors causes them to lose their biological incentive to stay with a mate, the human parallel is more nuanced. It is less about a total lack of loyalty and more about a difference in the brain's reward sensitivity. That is where the DRD4 gene comes in, which regulates dopamine, the brain’s ‘more’ molecule. Some people carry a variant that makes their brain less sensitive to dopamine, meaning routine happiness does not register with the same intensity. A study from Binghamton University found that people with this variant were twice as likely to report a history of uncommitted sex because the thrill of the forbidden provides a chemical hit that familiarity no longer delivers.

The brain’s mesolimbic reward pathway drives this dopamine-seeking behaviour. When this system is chronically under-stimulated, the prefrontal cortex — the part of the brain responsible for impulse control and long-term planning — can be effectively overridden by the limbic system's more immediate demands. It functions like a metabolic rate for emotional satisfaction; some people feel full on very little, while others are perpetually, neurologically hungry. However, having these genes does not doom a person to infidelity, and understanding the neuroscience is not the same as excusing the behaviour. Cheating remains universally condemned because neuroimaging confirms that romantic betrayal activates the same brain regions as physical pain. The anterior cingulate cortex fires like a distress signal during a breakup or betrayal, flooding the body with cortisol and a physical sense of grief.

For those wired with a loud ‘guilt complex’ — the type of person who loses sleep over a mildly awkward email sent three years ago — the cognitive dissonance of leading a double life feels impossible to sustain. Yet, for some, the guilt circuitry appears quieter, and the reward system simply drowns out the conscience. Ultimately, neuroscience offers a way to understand why the brain is susceptible to certain behaviours, which is the first step in making conscious choices to override them.

Of course, biology is only half the story. In a town as tiny as St Andrews, cheating is less of a moral choice and more of a logistical nightmare. When a single trip to Tesco means bumping into your partner, their best friend, and a secret fling all at once in the meal-deal aisle, ‘getting away with it’ becomes a physical impossibility. Perhaps the best way to keep people honest is not through willpower or genetic engineering, but simply by trapping them in a small town where everyone is always watching.

Image from Wikimedia Commons