When South Carolina Governor Mark Sanford was caught red-handed returning from a tryst with his Argentine mistress last June, he told the Associated Press that he had met his "soul mate." His choice of words seemed to suggest that having a deep emotional and spiritual connection with Maria Belen Chapur somehow made his sexual infidelity to his wife Jenny Sanford less tawdry.

What the two-timing governor didn't understand is that most women view emotional infidelity as worse, not better, than sexual betrayal. This may explain why Hillary Clinton stayed with Bill Clinton and seemed unconcerned about his sexual affair with Monica Lewinsky. Research has documented that most men become much more jealous about sexual infidelity than they do about emotional infidelity. Women are the opposite, and this is true all over the world. 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 now suggests an alternative explanation. The new study does not question the fundamental gender difference regarding jealousy -- indeed it adds additional support for that difference. But the new science suggests 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.

Pennsylvania State University psychological scientists Kenneth Levy and Kristen Kelly 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? The researchers suspected that it might have to do with trust and emotional attachment. 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.

Findings confirmed the scientists' hypotheses. As Levy & Kelly report in Psychological Science, a journal of the Association for Psychological Science, 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.

The scientists state that 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.

Additionally, placing jealousy within an attachment theoretical perspective, highlights the value of a taking a more nuanced approach relative to earlier research, points to new research possibilities, and suggests that promoting secure attachment may be an effective means of reducing the kind of sexual jealousy that contributes to domestic violence.