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.