How Is Personality Formed?
A Talk With Frank J. Sulloway

SULLOWAY: During the last two decades I have experienced a major shift in my career interests. I started out as a historian of science and was primarily interested in historical questions about people's intellectual lives. In trying to understand the sources of creative achievement in science, I gradually became interested in problems of human development and especially in how Darwinian theory can help us to understand the development of personality. I now consider myself a psychologist, in addition to being an historian.

JB: How did you make that leap?

SULLOWAY: This leap was determined by the kinds of questions I was asking. I was initially drawn to the problem of why scientists accept new ideas. If you survey the history of science, it is apparent that most individuals who have accepted radical innovations did not do so simply because they knew of some line of evidence that other people were unaware of. Darwin is a good case in point. He came back from the Beagle voyage and displayed his famous Gal�pagos specimens in London. Within six months of his return, most of the top naturalists in Britain had seen Darwin's Gal�pagos finches and reptiles, and hence the crucial evidence that converted Darwin to evolution (and that we now consider the textbook case of evolution in action). John Gould, who was one of the greatest ornithologists of the nineteenth century, knew far more about Darwin's Gal�pagos birds than Darwin did. Gould corrected numerous mistakes that Darwin had made during the Beagle voyage, such as thinking that many of the finches from the Gal�pagos Islands were the forms that they have come to mimic though biological evolution. For example, Darwin had mistaken the warbler finch for a warbler, and he had thought the cactus finch was a member of the Icteridae--a completely different family of birds. Gould corrected these errors and also showed Darwin that some of the other birds he had not recognized as finches were part of a single closely related group. Darwin was stunned by this and other crucial information that he received from Gould in March of 1837, and Darwin immediately became an evolutionist. The strange thing is that Gould did not. He remained a creationist even after The Origin of Species was published. Hence the man who knew more saw less, and the man who knew less saw more. It struck me that this puzzling episode in intellectual history had something to do with temperament, or character, or personality. It certainly didn't have anything to do with the scientific evidence per se. Darwin, Gould, and many other contemporary naturalists all knew about the same evidence. This leads to the inference that people who make creative leaps in science, and in other fields, do so in part because of their personalities-and more particularly because of their ability to think in new and unconventional ways. In short, I became interested in psychology.

JB: Was this a purely intuitive leap of mind?

SULLOWAY: There was certainly a lot of intuition involved in the leap. Fortunately, the intuitive leap was then followed up by hypothesis testing, which is a method that saves us all from becoming either astrologers or psychoanalysts.

I see the mind as an exquisitely engineered device�not literally engineered, of course, but designed by the mimic of engineering that we see in nature, natural selection. That's what "engineered" animals' bodies to accomplish improbable feats, like flying and swimming and running, and it is surely what "engineered" the mind to accomplish its improbable feats.

JB: How did this idea creep into your consciousness?

SULLOWAY: It was partly intuition, and it was partly just hard evidence. In the early 1970s I began reading everything I could find in personality psychology, especially the literature on cognitive style, and I also began doing research in this area. Eventually I stumbled onto the topic of birth order, on which I subsequently spent two decades doing research. Birth order, however, was just the tip of the iceberg in this research project. The minute one begins to deal with the issue of family dynamics, one also encounters other important factors that are causing personality to develop the way it does.

JB: What was your background?

SULLOWAY: I was a first-year graduate student when I developed the interests that have marked my work on scientific creativity. I was just beginning to do my preliminary course work for a degree in the history of science. At that time I anticipated writing a doctoral dissertation on Darwin's life. I had done quite a bit of research on Darwin. For example, I had retraced the Beagle voyage around South America and I had made a series of films on Darwin's voyage. I also knew a great deal about Darwin's conversion to evolution, and the specific reasons why Darwin converted; and I had begun to write various papers on these topics-papers that eventually became published articles. In hindsight, I had stumbled onto a problem-Darwin's conversion-that completely changed by career. At one point I seriously considered getting a joint degree in psychology, and did most of the necessary course work in this field. Although I did not end up taking a joint degree, I had entered into what became a kind of hybrid career path. I continued to do considerable reading and research in psychology; I kept up my previous interests in evolutionary biology; and I also continued with my researches in the history of science-particularly on the topic of revolutions in science.

JB: Where were you at the time?

SULLOWAY: I was a graduate student at Harvard University. About two years into my graduate studies period I became a Junior Fellow in the Society of Fellows, and this was a wonderful experience. Being a Junior Fellow freed me to work in any area that I wanted. I was no longer under the direct supervision of anyone in my department. It was a terrific experience, and I thrived on the independence it provided.

JB: Let's talk about the thesis that led you to your book Born to Rebel.

SULLOWAY: Essentially what I stumbled on in 1970, and then empirically verified over a 20-year period, is that aspects of personality that are under environmental control are strongly influenced by family niches. Birth order is particularly important in this regard, because it is a systematic source of differences in family environments. But birth order is not a cause, in and of itself. Rather, it's a surrogate, or a proxy, for patterns of family dynamics that are actually molding personality. For example firstborns are bigger than their younger siblings. They also are older and tend to have more status. In competition with their siblings, there are certain strategies that eldest children can employ that younger children cannot. A younger child can decide to hit an elder sibling, but this is usually not a smart idea because the elder sibling can hit back harder. In general firstborns tend to be more aggressive; they use strategies and tactics that take advantage of their greater physical size.

There is an important dimension of personality called "agreeableness/antagonism"—one of the Big Five—that exhibits significant differences by birth order. This birth-order difference reflects difference in the niches that firstborns and younger children typically occupy. Firstborns tend to occupy the niche of a surrogate parent. Acting as a surrogate parent-that is, assisting with child-rearing duties-is a great way to curry favor with parents. For this reason, firstborns tend to identify more closely with their parents, and they also tend to identify with whatever their parents value. Parents value a child's doing well in school, so firstborns are conscientious, do their homework, generally do better at school, and tend to be over-represented as academics and in Who's Who. The niche of the responsible achiever is particularly likely to be open for an eldest child. Once this niche is taken, it is difficult for a younger sibling to compete effectively for the same niche, although they often try. The typical strategy of younger siblings is to see whether they can compete successfully in a niche already occupied by an elder sibling. If they cannot, then the best strategy is for the younger sibling to branch out—to become more open to experience—and to try to find some alternative niche where they will not be directly compared with their elder siblings. If an elder brother is a great spear-thrower and a younger cannot top that, they might as well take up the bow and arrow. And if there is another older sibling already specializing in the bow and arrow, then it pays to invent the crossbow. The general rule, then, is do something different that adds value to the family unit as a whole. Like Darwin's famous finches, younger siblings are busy diversifying: They are trying to radiate adaptively away from whatever specialized abilities are already represented by siblings who are older than themselves.

These "contrast effects" between siblings explain the relationship between birth order and certain kinds of creativity. Younger siblings are much more likely to accept radical innovations in science and in social thought. Within their own families, they are at the bottom of the pecking order, so they tend to identify more with the underdog and to champion egalitarian causes. Younger siblings were the earliest backers of the Protestant Reformation, and after it the Enlightenment. Most lost causes in history have been supported by younger siblings and opposed by firstborns. This historical difference goes directly back to the kind of psychological differences in strategic niches that siblings occupy within the family constellation.

JB: You have stated that younger siblings have more in common with their peers than their siblings.

SULLOWAY: On average, firstborns are more similar in personality to firstborns in other families than they are to their own younger siblings. Similarly, a youngest child in one family is often more similar to a youngest child in another family than to his or her own elder siblings. Still, all laterborns are more similar to one another, on average, than they are to firstborns.

JB: How did you test this hypothesis?

SULLOWAY: There are several ways of testing it. In my book Born to Rebel, I engaged in two major empirical assaults on this problem. The first method of attack involved historical evidence. I gathered data on more than 6,500 participants in major revolutions in science, politics, and social thought. In addition, I arranged for each individual's position in each controversy to be validated by half a dozen or more expert historians. Overall, I asked 110 historical experts to examine my lists of participants in revolutions, and to assess whether these lists were representative of participants as a whole. My experts were also asked to nominate missing individuals, and they rated every participant on a scale of acceptance and rejection. Obtaining these expert ratings involved a tremendous amount of work, in part because I did it in person. I flew a quarter of a million miles around the world as I gathered these expert ratings from scholars in England, France, Germany, Italy, and America. My second line of research involved a reassessment of the birth-order literature as a whole. There are more than 2,000 publications on this subject, and what was needed was a meta-analysis to determine whether there are more significant findings than would be expected by chance. In my meta-analysis I tested specific hypotheses about sibling strategies, using the Big Five personality dimensions as my guide. That is, I expected firstborns—relative to laterborns—to be more (1) conscientious, (2) aggressive, (3) conventional, (4) extraverted in the sense of being dominant (laterborns are more extraverted in the sense of being sociable), and (5) emotionally volatile, in the sense of being quicker to anger. All five of these hypotheses were confirmed by my meta-analysis, which involved a statistical survey of 196 birth-order studies controlled for social class and sibship size.