Note: Anger, envy, gluttony, greed, lust, pride and sloth. Whether or not committing one of these sins will destine you to an eternity stoking Satan’s furnace is up for debate but one thing’s for sure, committing them in a relationship may leave you all alone and out in the cold. In this seven-part series, writer Michael Kerr explores each of the seven deadly sins and why they’re bad for couples.

The Seven Deadly Relationship Sins: Lust

“I’ve looked on many women with lust. I’ve committed adultery in my heart many times.” – Jimmy Carter

Former U.S. president Jimmy Carter isn’t the only one who’s committed lust in his heart; if you’re a man, you have too. That’s just the way we’re wired. Blame it on another U.S. president: Calvin Coolidge. The so-called “Coolidge effect” is the tendency of the males of most species of mammals to seek out variety in sexual partners. Research has shown that, when, say, a male rat is introduced to a new female, he copulates like crazy with her at first. Over time, however, his interest begins to wane until he has almost no libido left. That is, until a new female is introduced, then it’s “game on” all over again. The Coolidge effect has been recorded again and again in species ranging from sheep to primates and, yes, even humans.

How the Coolidge Effect Got Its Name

One day, so the story goes, the first couple was visiting a government farm in Kentucky. While taking separate tours of the facility, the first lady was escorted past a chicken pen. Mrs. Coolidge paused and asked her guide how many times each day the rooster “performed his duty.” The guide replied, “Dozens of times, Mrs. Coolidge.” “Please tell that to the president,” she slyly retorted. When the president was told of the rooster’s prowess he became skeptical. “Is it always with the same hen?” “Oh no, Mr. President, it’s a different hen each time,” said the guide. The president, nodded, smiled and said, “Please tell that to Mrs. Coolidge!”

Lust and Relationships

Of course the story is funny because it’s relatable. Unfortunately, when it comes to most relationships, the Coolidge Effect becomes untenable. Human beings in the U.S., for the most part, have agreed on a slightly less open arrangement than that Kentucky rooster was obliged to—one that typically involves just two people “until death do us part.” Of course, we’re neither rats nor sheep, and can (theoretically) control our urges. But at what cost?

The Price of Infidelity

A 2011 study found that it’s not only men who are acting on their lust—more and more; women are getting a little strange too. The study, published in the Archives of Sexual Behavior, found that, among heterosexual couples, nearly one-quarter of men (23.2%) and almost one fifth of women (19.2%) admitted to “cheating” during their current relationship. The General Social Survey, which has tracked “opinions and social behaviors” of Americans since 1972 finds that, in a given year, 12 percent of men and 7 percent of women will have sex outside of their marriage. Infidelity is the leading cause of divorce; cited in nearly 25 percent of breakups.

Lust vs. Love: The Ultimate Cage Match

The problem with lust in some relationships may not be that one partner is lusting after someone else—it may be that you got into your relationship based on lust rather than love in the first place. In an article in Psychology Today, relationship expert Judith Orloff, M.D. calls lust an “altered state of consciousness programmed by the primal urge to procreate.”  To avoid mistaking lust for love, especially in the early stages of a relationship, she recommends listening to your gut. While lust can certainly exist in a relationship based on love, it rarely works the other way around.

Signs you may be in lust rather than love according to Orloff:

• You’re focused on the other person’s looks or body
• You’d rather have sex than conversations
• You prefer to keep things “on a fantasy level,” and not deal with real feelings
• You are compelled to leave soon after sex
• You’re not friends with the other person outside of the bedroom

On the other hand, love tends to contain the following signs:

• You want to spend quality time with the other person in addition to sex
• You tend to get lost in conversations together
• You’re concerned about the other person’s feelings and happiness
• You want to be a better person
• You want to get to know the other person’s friends and family

Keeping That Loving Feeling

So you’ve chosen the right person, but what happens when the inevitable lusting in the heart becomes lusting for a co-worker or a stranger on the bus? According to Barry McCarthy, PhD, a certified marital and sex therapist, one way to either avoid or recover from affairs is to “re-eroticize the marriage.”

Because much of the excitement of affairs has to do with their illicit nature, McCarthy recommends bringing that affair-like exhilaration into a monogamous union—both in and out of the bedroom. The point, he says, “is to abolish the inclination to compare marital sex with affair sex”—something he calls a hopeless cause. Between kids, work and other pressures, it can be challenging to keep the lust at home. “But in the long run, it’s in everyone’s best interest,” he says.

When he’s not penning posts for Tokii, award-winning Portland, Oregon writer Michael Kerr takes solace in uncomfortable silences.