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Why do men, particularly middle-aged men, cheat on their spouses? Some recent scientific research has found that just talking with a woman (or for a gay man, with a man) raises testosterone levels.

Just talking with a woman raises testosterone levels

Testosterone is essential to male health, not just sexual health. Testosterone is responsible for bone growth, muscle growth, and blood sugar regulation in men throughout their lives. Just a few of the symptoms of low testosterone levels include:

  • Body hair loss
  • Diminished sex drive
  • Increased fat mass, which increases production of estrogen (Fat cells make estrogen in both sexes.)
  • Irritability, sometimes in a syndrome mimicking premenstrual syndrome, known as Irritable Male Syndrome
  • Lack of energy and youthfulness
  • Muscle loss
  • Weight gain

The production of testosterone by a man's body declines gradually after the age of 30, and the tendency to have affairs increases after the age of 30. But to really understand the relationship between testosterone and cheating on one's wife, it's first importance to understand the hormonal difference between love and sex.

In the brain as well as below the belt

Love stimulates hormones in a man's brain. When a man views a photograph of his wife, assuming they have a happy relationship, levels of the pleasure chemical dopamine go up. This is the same hormone that is stimulated by winning at sports, gambling, sex, and eating cheeseburgers. A man's dopamine levels are also elevated by looking at photographs, again, assuming there is a happy relationship, of his children, parents, friends, and pets.

Men are hardwired to have real feelings of love and loyalty that are not sent through the same circuits as their feelings about sex. Men may protect their wives and children with fierce, self-sacrificing loyalty, but still feel the urge to mate outside their marital bond.

Sex stimulates different hormones in a man's brain. Just talking to a woman can raise a man's testosterone levels--as long as the talk isn't about relationships. The talk that raises a man's testosterone levels is active, manly talk, about doing, not about feeling. And having sex also raises a man's testosterone levels, and, a clinical study conducted in Italy found, even increases the size of his penis and testicles.

Swelling of a more permanent kind

Scientists at the Andrology Unit of the University of Florence in Italy found that men who have affairs tend to grow larger sex organs, are less likely to need medication for erectile dysfunction, are more interested in sex (with their wives and with other women), have more sex with their wives, and report less guilt about autoeroticism. This explains why infidelity in middle aged men is not a simple matter of dissatisfaction with their marriages, and may not involve marital dissatisfaction at all. For some men, having an affair is a socially permitted expression of a biological urge.

Scientists have observed that the males of the primate species that have one mate at a time, such as gorillas and gibbons, have much smaller testicles relative to body size than the males of the primate species that have multiple mates whenever possible, such as the bonobos and chimpanzees. Some scientists believe that prior to the introduction of agriculture, when humans hunted and gathered in lose tribal groups, sexual relationships were not exclusive, and our human ancestors also had much larger testicles and much higher levels of testosterone. These same scientists note that as society has become much more complex and it's possible to monitor marital fidelity much more closely (the male frontier explorer who had a one night stand probably did not have to deal with the consequences), sperm counts have fallen precipitously over the last few decades.

Some scientists also note that gay men are usually not monogamous. They explain that gay men have had to go through a process in which they learn the real nature of their sexuality, and part of that nature is not to have sex with just one (male) person. Gay men usually do not consider sex and love to be the same.

Psychotherapists also report that about 35 to 55 per cent of their male patients who have affairs don't have affairs because they are dissatisfied with their marriages. Psychoanalyst Tammy Nelson has gone so far as to describe a "new monogamy" in which marriages do not necessarily end just because one partner has had a sexual relationship outside the marriage.

New monogamy - marriage as a fluid relationship

The new monogamy, Dr. Nelson says, is a recognition that marriage may be a more "fluid" relationship than in its traditional definition. Both husband and wife assume that they will remain the primary attraction to each other, but they tolerate and sometimes even support occasional sexual relationships outside the marriage.

What makes those relationships work, according to Dr. Nelson, is complete honesty between husband and wife. Fidelity means that husband and wife are honest with each other, sparing each other the traditional lies, deceptions, and manipulations that lead partners to have even greater doubts about the love that is the foundation of the marriage. As Dr. Nelson told Psychology Today, "Rightly or wrongly, today, many couples consider that honesty and openness cleanse affairs, rendering them essentially harmless."

These relationships are not polygamy (one husband having multiple wives) or polyandry (one wife having multiple husbands) or polyamory (having multiple people of both genders in a marital relationship). They are simply a recognition that husbands and wives are human, and that the choices and rules the couples make and keep for themselves are more important to them than the choices and rules society makes for them.

The strength of your marriage is what you choose it to be

While men may choose to be faithful to their spouses, and even men who cheat may want to stay married, Nelson believes that it is unrealistic to expect youthful passion to last forever. Understanding why men cheat can help women process why an affair happened, and to make their choices to leave the marriage, to allow matters to stay as they are, or to make the marriage stronger.

  • Fisher AD, Corona G, Bandini E, Mannucci E, Lotti F, Boddi V, Forti G, Maggi M. Psychobiological correlates of extramarital affairs and differences between stable and occasional infidelity among men with sexual dysfunctions. J Sex Med. 2009 Mar,6(3):866-75. Epub 2009 Jan 8.Photo by