Correspondingly, monogamy and commitment are more commonplace.
In marital relationships, exclusivity expectations are commonly assumed although they are not always met.
When they are not met, research has found that psychological damage can occur, including feelings of rage and betrayal, lowering of sexual and personal confidence, and damage to self-image.
There is currently debate in the field of evolutionary psychology whether an innate, evolved sex difference exists between men and women in response to an act of infidelity; this is often called a "sex difference".
Those that posit a sex difference exists state that men are 60% more likely to be disturbed by an act of sexual infidelity (having one's partner engage in sexual relations with another), whereas women are 83% more likely to be disturbed by an act of emotional infidelity (having one's partner fall in love with another).
Depending on the context, men and women can experience social consequences if their act of infidelity becomes public.
The form and extent of these consequences are often dependent on the gender of the unfaithful person.One measure of infidelity among couples is the frequency of children secretly conceived with a different partner, leading to "non-paternities".Such covertly illegitimate children amount to about 1–2% of newborns in studied populations.Results, however, vary year by year, and also by age-group surveyed.For example, one study conducted by the University of Washington, Seattle found slightly, or significantly higher rates of infidelity for populations under 35, or older than 60.These differences have been generally thought due to evolutionary pressures that motivate men towards sexual opportunity and women towards commitment to one partner.