I'm quoting in length along, with my comments, the study be Madeline Elis about the behavior of certain genes that may be the answer.

Each genes has a special job to do, but what happens when genes don't work right or have changed in some way?

Researchers think that altered or mutated genes are partly the blame for lung problems, cancer, and many other ill­nesses. And now, scientists believe a certain gene variant may be linked to marital monogamy.

For their study, a team looked at 552 Swedish twins and their patterns of at least five years.

Most (82%) were married and 18% were living together but not married. They had DNA tests, were given a questionnaire, and were visited at home by the researchers. They were also given a test that estimates how bonded one is to one mate. The men who had the gene vari­ation, called 334 allete, scored lower on the bonding test and were not as likely to be married as men without the gene variation.

And men carrying two copies of the allete, were twice as likely to have a dysfunctional marriage, including a threat of divorce. Fifteen percent of the men carrying 334 allete reported marital crisis, where 34 % of the men carrying two copies of this allete reported marital crisis, the researchers reported.

Partners of the men without the gene variation reported that they were the most satisfied with their relationship.

The study suggests that two of every five men, have this gene variation.

The team isn't sure that the variation does do a man's behavior, but it believes it has to do with their ability to communicate and show compassion.

However, Walum stressed that larger studies need to be done to test how the variant affects a human being's behavior and says other factors, such as culture, religion, and family background also shape a man's marital behavior.

So, does having allete provide a rationale for cheating?

Experts say -NOT AT ALL.

However, being that you have a genetic variance can provide the community to treat it, much the same as providing skills to someone who is having social difficulty.

And just as the alcoholics avoid bars and liquor stores, people who feel they are at risk of cheating should avoid situations that may lead them to temptation, such as regularly car pooling with a worker of the opposite sex or going out to clubs or bars at night without their spouse.

There things we do because we know we should, and most of them are not the easiest choices.

Everyone is capable of deciding to be faithful to their significant other, regardless of their genetic make up.