Research has documented that most men become much more jealous about sexual infidelity than they do about emotional infidelity. Women are the opposite. The prevailing theory is that the difference has evolutionary origins: Men learned over eons to be hyper-vigilant about sex because they can never be absolutely certain they are the father of a child, while women are much more concerned about having a partner who is committed to raising a family.

New research conducted by Pennsylvania State University psychologists now suggests an alternative explanation. The study argues that the difference may be rooted more in individual differences in personality that result from one's relationship history but that can fall along gender lines. The findings appear in Psychological Science.

The researchers doubted the prevailing evolutionary explanation because there is a conspicuous subset of men who like most women find emotional betrayal more distressing than sexual infidelity. Why would this be? Some people—men and women alike—are more secure in their attachments to others, while others tend to be more dismissive of the need for close attachment relationships.

Psychologists see this compulsive self-reliance as a defensive strategy—protection against deep-seated feelings of vulnerability. Levy and Kelly hypothesized that these individuals would tend to be concerned with the sexual aspects of relationships rather than emotional intimacy.

Similar to earlier studies examining sex differences in jealousy, Levy and Kelly asked men and women which they would find more distressing—sexual infidelity or emotional infidelity. Participants also completed additional assessments including a standard and well validated measure of attachment style in romantic relationships.

The authors say the findings confirmed their hypotheses: those with a dismissing attachment style— who prize their autonomy in relationships over commitment—were much more upset about sexual infidelity than emotional infidelity. And conversely, those securely attached in relationships—including securely attached men—were much more likely to find emotional betrayal more upsetting.

These findings imply that the psychological and cultural-environmental mechanisms underlying sex differences in jealousy may have greater roles than previously recognized and suggest that jealousy is more multiply determined than previously hypothesized.