A growing body of research suggests that certain people are more likely to be unfaithful, depending on their biology.
For example, one study from the University of Queensland, published in the journal Evolution and Human Behavior, found that infidelity was more common among people who had specific types of oxytocin and vasopressin receptor genes.
As Richard Friedman, a professor of clinical psychiatry at Weill Cornell Medical College, explained in The New York Times, vasopressin is a hormone related to social behaviors including trust, empathy, and sexual bonding.
According to the results of that study, a whopping 40% of instances of infidelity in women and 62% in men had to do with genetics.