Whatever happened to fidelity?

You have to wonder. And this analysis from the New York Times doesn’t provide any easy answers:

A handful of new studies suggest surprising changes in the marital landscape. Infidelity appears to be on the rise, particularly among older men and young couples. Notably, women appear to be closing the adultery gap: younger women appear to be cheating on their spouses nearly as often as men.

“If you just ask whether infidelity is going up, you don’t see really impressive changes,” said David C. Atkins, research associate professor at the University of Washington Center for the Study of Health and Risk Behaviors. “But if you magnify the picture and you start looking at specific gender and age cohorts, we do start to see some pretty significant changes.”

The most consistent data on infidelity come from the General Social Survey, sponsored by the National Science Foundation and based at the University of Chicago, which has used a national representative sample to track the opinions and social behaviors of Americans since 1972. The survey data show that in any given year, about 10 percent of married people — 12 percent of men and 7 percent of women — say they have had sex outside their marriage.

But detailed analysis of the data from 1991 to 2006, to be presented next month by Dr. Atkins at the Association for Behavioral and Cognitive Therapies conference in Orlando, show some surprising shifts. University of Washington researchers have found that the lifetime rate of infidelity for men over 60 increased to 28 percent in 2006, up from 20 percent in 1991. For women over 60, the increase is more striking: to 15 percent, up from 5 percent in 1991.

The researchers also see big changes in relatively new marriages. About 20 percent of men and 15 percent of women under 35 say they have ever been unfaithful, up from about 15 and 12 percent respectively.

Theories vary about why more people appear to be cheating. Among older people, a host of newer drugs and treatments are making it easier to be sexual, and in some cases unfaithful — Viagra and other remedies for erectile dysfunction, estrogen and testosterone supplements to maintain women’s sex drive and vaginal health, even advances like better hip replacements.

“They’ve got the physical health to express their sexuality into old age,” said Helen E. Fisher, research professor of anthropology at Rutgers and the author of several books on the biological and evolutionary basis of love and sex.

In younger couples, the increasing availability of pornography on the Internet, which has been shown to affect sexual attitudes and perceptions of “normal” behavior, may be playing a role in rising infidelity.

But it is the apparent change in women’s fidelity that has sparked the most interest among relationship researchers. It is not entirely clear if the historical gap between men and women is real or if women have just been more likely to lie about it.

“Is it that men are bragging about it and women are lying to everybody including themselves?” Dr. Fisher asked. “Men want to think women don’t cheat, and women want men to think they don’t cheat, and therefore the sexes have been playing a little psychological game with each other.”

Dr. Fisher notes that infidelity is common across cultures, and that in hunting and gathering societies, there is no evidence that women are any less adulterous than men. The fidelity gap may be explained more by cultural pressures than any real difference in sex drives between men and women. Men with multiple partners typically are viewed as virile, while women are considered promiscuous. And historically, women have been isolated on farms or at home with children, giving them fewer opportunities to be unfaithful.

But today, married women are more likely to spend late hours at the office and travel on business. And even for women who stay home, cellphones, e-mail and instant messaging appear to be allowing them to form more intimate relationships, marriage therapists say. Dr. Frank Pittman, an Atlanta psychiatrist who specializes in family crisis and couples therapy, says he has noticed more women talking about affairs centered on “electronic” contact.

“I see a changing landscape in which the emphasis is less on the sex than it is on the openness and intimacy and the revelation of secrets,” said Dr. Pittman, the author of “Private Lies: Infidelity and the Betrayal of Intimacy” (Norton, 1990). “Everybody talks by cellphone and the relationship evolves because you become increasingly distant from whomever you lie to, and you become increasingly close to whomever you tell the truth to.”