Why Him? Why Her?

“Now you will feel no rain, for each of you will be shelter to the other. Now you will feel no cold, for each of you will be warmth to the other. Now there is no more loneliness for you. But there is one life before you. Go now to your dwelling place, to eat to your days together. And may your days be very long upon this earth.”

The Apache Indians of the American Southwest probably recited this wedding poem for centuries before I heard it in La Jolla, California, in 2006. It was an early June evening, the sky still pink and blue, the sea smells wafting through the windows as I sat in a folding chair on the second story of a fancy Italian restaurant. An older gentleman was conducting a short wedding ceremony, one mixed with rituals from the Christian, Jewish and Apache traditions. And before me glowed the two celebrants, Patrick and Suzanne—one of the first couples to marry after meeting on the Internet dating site I had helped to design, Chemistry.com.

Patrick had been a journalist in New Orleans until he lost his job, his home and all of his belongings to Hurricane Katrina in 2005. West he went, taking up residence with relatives in Los Angeles in February 2006. Days after settling in, he joined Chemistry.com and received his first recommended match: Suzanne, a lawyer living in La Jolla. That first night they talked for three hours on the phone. They met the following weekend and fell passionately in love.

I like being around people who are in love. They have a contagious energy. This force was palpable in the groom, the first to arrive for the nuptials. He burst into the room, filling it with his vivacious charm. Although we had never met, he greeted me warmly. We instantly struck up a conversation about the evolution of the English language, his experience as a journalist in some dangerous parts of Asia and some of my past work on the brain chemistry of romantic love.

Others soon arrived, and we took our places on the folding chairs facing a small bar strewn with lilies. Last came the bride. I was stunned when I saw her—a tiny, perfectly formed, porcelain-like doll, with huge blue eyes and long auburn hair in soft ringlets wreathed in forget-me-nots. Like the mythological Helen, Suzanne had a face that could launch a thousand ships. And her vigor matched his. She was enraptured by her prince, gazing at him and grinning with uncontainable effervescence as she said “I do.”

Someone played a flute. The Apache poem was read. And as the bride and groom walked down the makeshift aisle between our seats, we blew bubbles at them from the little bottles left on our chairs.

“Love hopes all things,” the Bible says. I hoped for Patrick and Suzanne. But I also had a reason to be optimistic about their marriage. I knew some things about their personalities because both had taken my personality test, a series of questions I had devised to establish some basic things about a person’s biological temperament. Both had told me their test results. And from these data, I was confident that Patrick’s particular chemical profile would complement Suzanne’s, creating a biological and psychological cocktail that would keep them captivated with each other for years.

Temperament and Love

We have many inborn tendencies. Indeed, scientists now believe some 50 percent of the variations in human personality are associated with genetic factors. We inherit much of the fabric of our mind.

But what is personality?

Psychologists define it as that distinct cluster of thoughts and feelings that color all of a person’s actions.

Your personality is more than just your biology, of course. Personality is composed of two fundamentally different types of traits: those of character and those of temperament.

Your character traits stem from your experiences. Your childhood games; your parents’ interests and values; how people in your community express love and hate; what relatives and friends regard as polite, dangerous or exciting; how they worship; what they sing; when they laugh; what they do to make a living and relax—these and innumerable other cultural forces combine to build your unique set of character traits.

The balance of your personality is your temperament, all of the biologically based tendencies you have inherited, traits that emerge in early childhood to produce your consistent patterns of feeling, thinking and behaving. As the Spanish philosopher JosŽ Ortega y Gasset put it, “I am, plus my circumstances.” Temperament is the “I am,” the foundation of who you are.

It is this part of the human spirit I had examined in Patrick and Suzanne—their biological temperament.

Born “Me”

No one knows precisely how many traits of temperament we human beings inherit. But studies of identical twins suggest we inherit many. Take the “giggle twins,” as they were called by staff members of the Minnesota Twin Study in the 1970s because these women would erupt with peals of laughter at the slightest jest or odd turn of phrase.

Daphne and Barbara were born to an unmarried Finnish student living in England in 1939. Barbara was adopted by an English groundskeeper who worked in a public park, while Daphne grew up in the home of a wealthy metallurgist. Yet when they first came together again at age thirty-nine as part of the Minnesota Twin Study, which focused on identical twins reared apart, both loved good pranks and both had giggled all their lives. Both regularly sat on their hands to keep from nervously gesticulating. Both had dyed their hair auburn. Both were effusively energetic. Both hated math and sports. Both avoided commercial television. Both preferred the color blue. Both were unwilling to give any political opinions. And both had met their husbands at age sixteen at a town hall dance and married in the autumn. Their IQ scores were nearly identical, too, despite Daphne’s expensive education and Barbara’s far more modest schooling.

Coincidence?

Psychologist Thomas Bouchard, director of the Minnesota Twin Study, unearthed so many stories like this one that in the 1980s he proposed that dozens of personality traits have a degree of heritability. Among those with the strongest genetic links, he reported, were traditionalism, the willingness to capitulate to authority, aggressiveness, the drive to lead and the appetite for attention. As he wrote in 1984, “Both the twin studies and the adoption studies converge on the surprising finding that common family environmental influences play only a minor role in the determination of personality.”

In recent decades human behavior geneticists have added substantially to this list of traits linked with our DNA. More important, scientists now know that groups of interacting genes influence behavior, even act together to create behavior syndromes. For example, if you have a biological appetite to seek novelty, you are also likely to be energetic, spontaneous, risk taking, curious and creative. If you are predisposed to be traditional instead, you are also likely to be loyal, cautious, respectful of authority and eager to make plans and follow schedules. We express constellations of related biological traits, creating what are commonly called personality types.

In fact, after doing extensive research on the biological underpinnings of personality types, I have come to believe that each of us expresses a unique mix of four broad basic personality types. Moreover, our primary personality type steers us toward specific romantic partners. Our biological nature whispers constantly within us to influence who we love.

These thoughts and more were swimming through my mind as I blew those bubbles at Patrick and Suzanne on that enchanting wedding evening. I thought both had found their soul mate.

Why are we naturally attracted to particular mates? My investigation of this mystery started over the Christmas holiday in 2004.

Match.com

“Why do you fall in love with one person rather than another?” This is what the executive team at Match.com wanted to know when I met with them two days after Christmas 2004 in New York City. Match.com is the world’s largest Internet dating site. And I had been invited to spend the day with them, thinking.

“No one really knows,” I responded.

Psychologists have determined that men and women tend to fall in love with individuals from the same ethnic and socioeconomic background; with those of a similar level of intelligence, education and physical attractiveness; with individuals holding similar religious, political and social values; and with those who have a similar sense of humor. We also fall in love when the timing is right; and often with someone who lives or works nearby. We tend to fall in love with someone who provides us with the things we need. And people often fall in love with those who are in love with them.

But, as I told the Match.com executives, how two individual personalities match up remains unknown. People do not necessarily court, live with or marry someone with similar or different personality traits. In fact, some 470 studies have examined the mesh of two personalities in a marriage. And psychologist Marcel Zentner summed up these data, saying, “Preference for similarity in personality characteristics varies substantially across traits and individuals.” As he put it, “How two personalities may be best combined in a relationship remains at present an unresolved issue.”

Yet your choice of mate will color every aspect of your life: your morning conversations in bed and at the breakfast table; your friendships, family reunions and weekend frolics; where you live; how you raise your children; most likely even your career. And certainly this choice will affect your tomorrows. Those babies you are likely to produce and send forth to multiply are your genetic future. Only a few times in your life will you mix your seed with that of another and pitch your DNA toward infinity.

So whom you choose matters.

In fact, I found it hard to believe that evolution would leave this decision entirely to our human whims. I suspected that psychologists had simply not looked for the underlying biological mechanisms that direct our romantic choices.

So when the folks at Match.com asked me to consider helping them develop a sister site for their Internet dating service, one designed for men and women interested in a long-term partnership, I said I would think about it during the festive midwinter lull.

The holiday season twinkled on. But on New Year’s Day I realized I had to come to grips with this opportunity—a chance to apply the newest data in neuroscience to the essential question of who you love, perhaps even help people find “the one.”

So I sat down at my empty desk and pulled out a blank sheet of paper. What did I know about personality?

The Biology of Personality

Dopamine. I began with this brain chemical because I had studied the activities of this powerful and ubiquitous neurotransmitter for several years.

On impulse, I listed some of the personality traits I knew were associated with specific genes in the dopamine system: the propensity to seek novelty; the willingness to take risks; spontaneity; heightened energy; curiosity; creativity; optimism; enthusiasm; mental flexibility. I decided to call those men and women who expressed the traits associated with this biology Explorers.

I drew another blank sheet of paper from my desk drawer. What else did I know about personality?

Well, individuals who have inherited particular genes in the serotonin system tend to be calm, social, cautious but not fearful, persistent, loyal, fond of rules and facts and orderly. They are conventional, the guardians of tradition. And because these men and women are also skilled at building social networks and managing people in family, business and social situations, I dubbed those who had inherited this constellation of genetic traits Builders.

I had also studied testosterone. Although testosterone is often associated with males, I knew that both men and women are capable of expressing particularly strong activity in this neural system. Moreover, those who inherit this chemistry tend to be direct, decisive, focused, analytical, logical, tough-minded, exacting, emotionally contained and good at strategic thinking. They get to the point. Many are bold and competitive. They excel at figuring out machines, mathematical formulas or other rule- based systems. Many are good at understanding the structure of music, too. I named these people Directors.

Last in my store of biological knowledge were some of the traits linked with estrogen. Women and men with a great deal of estrogen activity tend to see the big picture: they connect disparate facts to think contextually and holistically, expressing what I call web thinking. They are imaginative. They display superior verbal skills and excel at reading postures, gestures, facial expressions and tones of voice, known as executive social skills. They are also intuitive, sympathetic, nurturing, mentally flexible, agreeable, idealistic, altruistic and emotionally expressive. I christened the people of this broad biological type Negotiators.

Other chemical systems play a role in personality, of course. Two others should be mentioned. Norepinephrine, a chemical closely related to dopamine, undoubtedly contributes to some of the Explorer’s traits, especially their energy and impulsivity. And oxytocin—a chemical synthesized, stored and triggered (in large part) by estrogen—most likely plays a role in the Negotiator’s compassion, nurturing, trust and intuition. In fact, families of chemicals produce the Explorer, Builder, Director and Negotiator. The specific activities of any one chemical are not as significant as the ratios and interactions among all of them and several other neural systems.

Nevertheless, only dopamine, serotonin, testosterone and estrogen have been directly associated with a wide range of personality traits. So variations in these four chemicals most likely form the foundation of these four basic styles of thinking and behaving.

But does your personality type guide who you love?

I decided to find out.

The Personality Type Study

I accepted the consulting job as scientific adviser to what would become the new Internet dating site Chemistry.com. And in January 2005, I began to create the core statements in the questionnaire members would fill out when they joined this service, a questionnaire to establish their personality type. I based all my queries on genetics and neurochemistry.

For example, I posed the statement “I do things on the spur of the moment.” I reasoned that Explorers would be most likely to “strongly agree” because certain genes in the dopamine system are associated with impulsivity.

“My friends and family would say I have traditional values.” Because the drive to follow social norms is a hallmark of the serotonin system, I thought Builders would be particularly partial to this statement.

To establish the degree to which a member is a Director, I offered the statement “I am more analytical and logical than most people.” High-testosterone men and women, I believed, would feel this described them accurately.

And because Negotiators tend to be highly imaginative due in large part to estrogen activity, I included the statement “I vividly imagine both wonderful and horrible things happening to me.”

Then, with psychologists Jonathan Rich and Heide Island, whom I invited to join me on this project, I perfected the questionnaire. It was launched nationally as part of Chemistry.com in February 2006. The point of this test: to measure your biological profile for dopamine, serotonin, testosterone and estrogen—or the degree to which you are an Explorer, Builder, Director and Negotiator.

As I write this paragraph, some five million Americans have filled out the questionnaire, along with another 1.8 million in thirty four other countries, because this personality test forms the basis of the more extensive questionnaire and matching system used by Chemistry.com. And upon reviewing the data in a sample of 39,913 anonymous members of Chemistry.com, I vividly saw how differently each of these four personality types thinks and acts.

But I wanted to know more: Does each personality type like to do something different on Saturday night? What are their religious and political preferences? Do they pursue different vocations? Where does each type prefer to live? What kinds of friends does each type see regularly—a social crowd, intellectuals, adventurers or activists? How often does each type fall in love? What are their views on kissing in public? Do they regard sex as an important part of marriage? How much personal autonomy and closeness does each type need in a partnership? I was even curious about the state of their sock drawer: messy or neat?

So I also asked these and other questions and examined the responses in this same sample of 39,913 anonymous members of Chemistry.com. The group’s average age was thirty-seven; 56.4 percent were women; and 89.6 percent were heterosexual. Explorers were 26 percent of the sample, while Builders were 28.6 percent, Directors were 16.3 percent, and Negotiators were 29.1 percent of the population.

Sure enough, each broad personality type does fraternize with a different crowd, wants to live in a different place and has different religious values. These four types even doodle differently.

All the statistical data collected on this sample of 39,913 anonymous men and women, what I call the Personality Type Study—as well as information from genetics, neuroscience, anthropology, psychology and other scientific disciplines—form the basis of my understanding of Explorers, Builders, Directors and Negotiators.

The Mate Choice Study

Next, I needed to find out if a person’s biological temperament steers him or her toward a particular personality type as a romantic partner. I had some evidence that each type would be particularly suited to a specific other. Nevertheless, I did a second study, the Mate Choice Study, using statistical data on a different sample: 28,128 anonymous heterosexual members of Chemistry.com.

When I examined whom these men and women chose to meet, I saw nature’s plan: Explorers are attracted to other Explorers—people with many similar traits of temperament. Builders also gravitate to people like themselves, other Builders. Directors, however, gravitate to Negotiators. And Negotiators are drawn to Directors. These two personality types are attracted to individuals with a complementary temperament. Moreover, these patterns occur whether one is a male or female.

No wonder so many scientists and laymen think that “opposites attract” while so many others believe “birds of a feather flock together.” Both patterns occur—depending on your primary personality type. I felt as if I had sneaked into Mother Nature’s kitchen and stumbled on her recipes for who we love.

But how does an individual on an Internet dating site scan through an array of photographs and essays (profiles) and select, even recognize, individuals of a particular biological type?

As it turns out, our faces and our words say much about who we are.

What’s in a Face?

Take the iris of the eye. The crypts (or pits) of the iris and the furrows (the lines curving around the outer edge of the iris) are linked with specific traits of temperament. People with more furrows are more impulsive, as well as more willing to indulge their cravings—traits of the Explorer. Individuals with more crypts, however, are more trusting, warmhearted and tender—traits of the Negotiator.

Perhaps this is, in part, why we stare into the eyes of a potential lover, even in a photograph. We are unconsciously picking up subtle messages about temperament.

We signal even more about our temperament with the structure of our face. Chiseled and square jaws, high and prominent cheekbones, heavy brow ridges and broad high foreheads are all signs of testosterone activity, the primary chemical of the Director. Even women with elevated testosterone display many of these traits. Just look at the high cheekbones, broad chins and high foreheads of many female celebrities.

Both sexes also signal estrogen levels with their face. Clear smooth skin, full lips, small noses, round soft faces, delicate brow ridges and other babylike facial features all indicate high estrogen activity.

I have found no studies that report on the facial traits associated with dopamine, the dominant chemical of the Explorer, or serotonin, the primary chemical of the Builder. Nevertheless, I suspect Explorers and Builders both have distinctive facial signals—and someday scientists will discover them.

The Lure of Words

Explorers, Builders, Directors and Negotiators also signal their particular temperaments with their words.

This proposition has a history, known as the Lexical Hypothesis. In the 1930s, psychologists proposed that when individuals describe themselves they choose words and phrases that emphasize traits they regard as central to who they are. With time, these words become encoded in their speaking habits.

So using another statistical sample, this time of 178,532 anonymous men and women on Chemistry.com, I launched my Word Type Study. I composed a list of 170 words and examined how often each personality type used these words as they described themselves and what they were looking for in a mate.

Adventure is the word most often used by Explorers. The other nine of their top ten most-used words (in descending order) are venture, spontaneity/spontaneous, energy, new, fun, traveling, outgoing, passion and active.

Family is the most-used word among Builders. Following this, Builders are particularly partial to the words honesty, caring, moral/morals, respect, loyal, trust, values, loving and trustworthy.

Intelligent and intelligence together top the list of words used by Directors. But they also favor intellectual, debate, geek, nerd/nerdy, ambition/ambitious, driven, politics, challenge/challenging and real.

Can you guess the favorite words of Negotiators? Passion and passionate. These men and women also prefer real, heart, kind/kindness, sensitive, read/reader, sweet, learning/learn, random and empathetic/empathy.

Words, words, words. As Mark Twain said, “The difference between the right word and the almost right word is the difference between lightning and the lightning bug.” Words are verbal electricity. As members of Chemistry.com read the essays of potential partners, they apparently see specific words that instantly draw them to particular personality types.

Your Primary and Secondary Type

We are billboards of our genetic dispositions. And although each of us is a unique blend of all four personality types, we express some of these types more regularly (and more naturally) than others. I, for example, am predominantly an Explorer and secondarily a Negotiator. I have a few traits of the Director and even fewer traits of the Builder; and at times I can act “out of character.”

But I have come to think that both your primary and secondary biological type are central to your temperament.

Patrick, Suzanne’s new husband, certainly advertised his primary and secondary types: he is primarily a Negotiator and secondarily an Explorer. And Patrick showed many of the qualities of both these types minutes after he bounded into that Italian restaurant on his wedding night.

Foremost, Patrick was instantly likable; he had a fine-tuned sensitivity to those around him and a superb talent for handling people. He radiated warmth and authenticity. Moreover, Patrick “cared.” He spent his spare time teaching English to immigrants from Africa and Asia and sending supplies to war refugees in foreign camps. Indeed, his verbal skills, his easy way with people, his compassion and his mental flexibility enabled him to thrive in countries where few dare to work and many fail who do. Patrick was a Negotiator through and through.

But his secondary type, the Explorer, was also highly visible. Patrick was infectiously spontaneous. When asked during the wedding ceremony to sip some wine, he good-naturedly responded, “All of it?” During one of the rock numbers, he grabbed the mic and did an Elvis Presley imitation in his stately white wedding suit—the antics of the true social risk taker. And all evening, he wove through the balloons to every table and dragged complacent “singles” out to swing to the rock Ôn’ roll. Patrick was a fine blend of the verbal, imaginative, compassionate Negotiator and the energetic, novelty-seeking Explorer. Suzanne must have sized him up as soon as she saw his photo and read his essays on Chemistry .com.

I didn’t spend much time with Suzanne on her wedding night; she was understandably very busy. But she had told me she was primarily a Director and secondarily a Builder. So I could make some educated estimations about her temperament.

As a Director, Suzanne was most likely more focused than her new husband; she probably shot straight for her goals in a determined yet inventive way. Along with that gorgeous face and hourglass figure, Suzanne was almost certainly more forthright, analytical, exacting and autonomous, too. And as a Builder, she was probably more conscientious and cautious than her new mate.

The “Right” Fit

Most remarkable about that lovely wedding, Patrick and Suzanne fit one of nature’s patterns perfectly. As you recall, their primary types, the Negotiator and Director, gravitate to each other. Moreover, their secondary types, the Explorer and Builder, can balance one another, each providing strengths the other needs. So as I watched Patrick and Suzanne exchange their vows, then twirl around the dance floor, I found myself imagining how they would get along in the years ahead.

Would they still be in love fifty years from now?

I thought they would—for biological reasons.

Negotiators and Directors are very different in basic temperament. But these types can appreciate each other’s mode of thinking. Both like to imagine possibilities and generate theories. So Patrick and Suzanne will probably enjoy talking together for years about their insights and personal philosophies. Yet each will bring complementary skills to their conversations. While Patrick will see the big picture, Suzanne will probably know more about a smaller piece of the social, political or ethical puzzle. Each will almost certainly impress the other with their knowledge and ideas.

These two types value their independence, although Suzanne is likely to be far better at expressing her autonomy since Directors tend to be forthright and tough- minded. But Patrick will appreciate Suzanne’s frank, decisive nature—because Negotiators ruminate. They tend to live in an inner world full of soul-searching, options and ethical knots that keep them from making up their minds.

There will be mutual admiration, too. Suzanne is likely to admire Patrick’s imagination and insight and his ability to understand and deal effectively with people. She will also bask in his compassion, exuberance and sincerity. And her skepticism will balance Patrick’s easy trust.

But life won’t be all roses for this dynamic couple. Directors admire self-control; so at times Suzanne may think Patrick’s impulsivity is a bit over the top. She may become impatient with his intuitive side, too. Directors are logical, and the Negotiator’s flights of imagination can leave them feeling ungrounded. Meanwhile, Patrick may occasionally find Suzanne’s pragmatism maddening. Their secondary types, the Explorer and Builder, will also have an impact on their relationship: Patrick may occasionally feel hemmed in by Suzanne’s caution, while Suzanne may become annoyed when Patrick is impractical.

Nevertheless, nature has given Patrick and Suzanne many complementary primary and secondary traits. With this big boost from their biological dispositions, along with a bit of work and some luck, they have an excellent chance of remaining forever “in sync,” just the way they were as they swung around the dance floor that exhilarating wedding night: two very different individuals in perfect step with each other.

From the book Why Him? Why Her?: Finding Real Love by Understanding Your Personality Type by Helen Fisher. Copyright © 2009 by Helen Fisher. Published by arrangement with Henry Holt and Company, LLC. All rights reserved.