Jan. 26, 2009 -- The publisher provided the following excerpt of "Why Him? Why Her?: Finding Real Love by Understanding Your Personality Type," by Helen Fisher, to ABC News.
Watch an hour on the science of attraction Friday on a special edition of "20/20" at 9 p.m. ET
Chapter 1: Eavesdropping on Mother Nature
"I am large, I contain multitudes." -- Walt Whitman
"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.
So on a balmy evening during an April vacation together in Paris, Patrick took her to the top of the Eiffel Tower and proposed. The dazzled young woman grinned her "yes." So here I sat at a fancy Italian restaurant in La Jolla, surrounded by some fifty of their friends and relatives on this festive wedding eve.
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 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. Then came the feast: platters of Cavatelli Marinara, Antipasto Rustico, mussels, sausages, Chicken Fra Diavolo -- a host of Italian favorites appeared at every table amid the balloons, confetti and champagne as the disc jockey blasted out old tunes and we wildly danced. Patrick and Suzanne swirled among us, radiating joy.
"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 José Ortega y Gasset put it, "I am, plus my circumstances." Temperament is the "I am," the foundation of who you are. Curiosity; creativity; novelty seeking; compassion; cautiousness; competitiveness: to some degree, you inherit these and many other aspects of your disposition.
It is this part of the human spirit I had examined in Patrick and Suzanne -- their biological temperament.
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.
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 to this book, 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,1 creating what are commonly called personality types.2
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.
Who are you? Why are we naturally attracted to particular mates? My investigation of these mysteries started over the Christmas holiday in 2004.
"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. Midmorning, they asked me this fundamental question.
"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. Your childhood plays a huge role in your romantic choices, although no reliable patterns have ever been established. 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. Patrick, I would come to realize, had a good deal of the Explorer in him.
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. We may have as many as a hundred different kinds of neurotransmitters (smaller molecules) and some fifty types of peptides in the brain. But most keep the heart beating or orchestrate other basic functions. It is increasingly apparent that these four chemicals -- dopamine, serotonin, testosterone and estrogen -- play lead roles in producing aspects of personality.
Two others should be mentioned, though. 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.