What's the chemistry behind long-term marriage?

Fewer people are tying the knot these days.
Fewer people are tying the knot these days.
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From 1970 to 2010, the number of American women heading to the altar tumbled from 76.5 million to 34.9 million [source: The National Marriage Project]. That dip in marriage occurrence isn't indicative of cases of cold feet sweeping the nation, but rather a shift in how people approach the institution. Specifically, unwed couples are choosing more often to live together first and tie the knot later.

Dismal divorce statistics during those intervening decades may have also subliminally instilled concerns about the veracity of 'til-death-do-us-part. After all, romantic love isn't expected to burn brightly forever, at most smoldering into what psychologist Theodor Reik termed a "warm afterglow" in his 1944 book "A Psychologist Looks at Love" [source: Avecado and Aron]. Today, anthropologist Helen Fisher gives young lovers a brief four or five years before the honeymoon phase crests and wanes, correlating to the amount of time it takes to wean a child [source: Slater].

Is that brief window worth the $28,000 spent on the average wedding [source: Clark]? Of course, there isn't a correct blanket answer for everyone. Fortunately, contemporary researchers peeking into the interpersonal and neurological pathways and logjams of long-term love have uncovered a host of ingredients for making it work. The only trouble is some are completely out of our control, at times rendering us defenseless to the whims and wherefores of romance.

In 2008, for instance, Swedish researcher Hasse Walum identified a male gene variation linked to relationship instability [source: Greenfieldboyce]. Men with altered versions of the so-called "fidelity gene" weren't necessarily more likely to cheat but scored lower on measures of partner bonding, such as how often they kiss [source: Greenfieldboyce]. Then again, Walum cautioned that the complexity of romantic relationships undoubtedly outweighs the influence of DNA.

Interpersonal Ingredients: Hallmarks of Happy Couples

A long-term, enjoyable marriage is possible.
A long-term, enjoyable marriage is possible.
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It doesn't take a trained statistician to guess certain key ingredients to a happy marriage. According to the 2011 report from the National Marriage Project, husbands and wives cited sexual satisfaction, commitment and positive attitudes about child-rearing among their respective must-haves [source: Luscombe]. Add to that solid communication skills and extramarital social support, and the basic toolbox for weathering the years together is filled [source: Parker-Pope].

But pursuing love throughout a marriage also involves a degree of selfishness, come to find out. Stony Brook University psychologist Arthur Aron emphasizes the importance of finding self-expansion in a marriage as means to long-term satisfaction [source: Parker-Pope]. Couples that stoke each other's senses of learning, adventure and intrigue -- either alone or side by side -- are unwitting experts in self-expansion, seeking novel experiences that enrich themselves and, by extension, their relationships. In exchange for that self-expansion, satisfied partners statistically perform five acts of generosity for every one instance of bickering or whatnot [source: Parker-Pope].

If those are the mechanics of a long-term, enjoyable marriage, what does that lasting sweetness feel like? In short, it feels a lot like falling in love. In 2009, psychologists Bianca P. Acevedo and Arthur Aron at Stony Brook University debunked the common gloomy notion that romance eventually fades as a marriage ages. What ebbs over time, rather, is obsession. As couples bond over the years, the passion doesn't necessarily dwindle, just the overwhelming obsession and anxiety that initially came with the budding relationship [source: Acevedo and Aron]. Early-stage romantic love is characterized by a nagging obsession for one's beloved, so strong and blindsiding that it's considered a threat to the human metabolism, gobbling up an astonishing amount of focus and energy [source: Fisher]. In that light, successful marriages are akin to trading out honeymoon suites for penthouses.

At the same time, that isn't to say that making marriages work is a cinch, as evidenced by the fact that Americans' lifetime chance of divorce hovers between 40 and 50 percent [source: National Marriage Project]. For all of these interpersonal tips for nuptial bliss, the difference between the couples who do and don't endure can be seen clearly in the brain.

Neurological Necessities: Long-term Love in the Brain

Love stays alive in the brain for the long haul.
Love stays alive in the brain for the long haul.
Dimitri Vervitsiotis/Getty Images

From an evolutionary perspective, that mind-altering joy of romance ensures that humans not only will want to reproduce, but also stick around long enough to rear a child. For that reason, UCLA psychologist Martie Haselton, who studies our primal compulsions to mate, sterilely refers to love as a "commitment device," reinforced by natural selection to direct our attention toward hearth and home [source: Zimmer]. In slightly sweeter terms, the human brain -- thanks to natural selection -- processes romance like a box of chocolate.

The limbic reward system that similarly springs to action when we receive cash bonuses or sip on a glass of bubbly reacts positively to wooing someone who tickles our fancy. Functional MRI (fMRI) technology has illuminated the specific areas of the brain aroused in people freshly in love, which explain the swirl of positive and negative emotions that wash over us when we're blissfully together and fretfully apart. In 2010, a team of researchers compared that fMRI data to brain scans of people who had been married around 20 years and reported still being in love with their partners [source: Acevedo et al]. Despite the multiple years since first locking eyes, the brain activity among those experiencing head-over-heels new love and those who had been together for decades appeared remarkably similar.

When shown photographs of their respective partners, two key brain regions lit up excitedly in both sets of people: the ventral tegmental area (VTA) in the center of the brain and the nearby caudate nucleus [source: Acevedo et al]. Those structures help drive motivation and decision-making in pursuit of reward. The prize of being with their beloved refreshes people's pleasure-inducing dopamine supply in their brains. In addition, those neurological regions are packed with receptors for oxytocin and vasopressin, neurochemicals that promote bonding and monogamy.

What didn't sparkle at the sight of the long-term lover were areas associated with anxiety and fear, such as the amygdala. As mentioned on the previous page, self-reported psychological surveys and assessments denote the absence of addled obsession among people who were happily married for an extended period of time. Instead, brain sites that also promote maternal attachment lit up at the sight of a life partner, demonstrating how that obsessive early-stage love gives way to calmly passionate commitment. But aside from that maturational distinction, the primary chemicals that preserve long-term marriage -- dopamine, oxytocin and vasopressin -- are the same ones that gave us goose bumps to begin with.

For the 40 percent or so of modern marriages ending in divorce, those neurotransmitters eventually wear their welcome, and the brain's reward system develops a tolerance of sorts for respective partners -- similar to how an addict might develop a tolerance for a certain amount of drugs over time [source: Fisher]. The sizzle fizzles, sapping the interpersonal spice that initially drew two people together. Yet from a more sentimental stance, that's also what makes long-term love such a treasured bond -- it's rare to find and even rarer to preserve 'til death do you part.

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Sources

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