JB: Are there any particular people mounting the attack?

SULLOWAY: The critics have not been connected by any single discipline. The most interesting responses to the book are now coming from psychologists who are busy trying to test and replicate some of my findings. This is becoming an interesting source of potential controversies for the following reasons. There are already more than 2,000 studies on birth order, and more than half of those studies show no significant findings. How can this be, if birth order has an important influences on personality? The answer is twofold. The first part of the answer is that self-report data are not all that reliable. If I had been able to ask Robespierre whether he was a mean and vindictive fellow, I don't think he would have replied in the affirmative. If I had been able to ask Darwin's staunch American opponent, Louis Agassiz, whether he considered himself reluctant to accept new ideas, he would rightfully have said, "No, I am very open to new ideas. I was a pioneer in the development of glaciation theory." Agassiz's openness to the theory of the Ice Ages is not inconsistent, however, with his vehement opposition to evolution. Evolution was a radical innovation, whereas glaciation theory was a somewhat conservative innovation closely allied to catastrophism. Agassiz later used glaciation theory as a conceptual weapon against evolution, claiming that each Ice Age had extinguished life on earth, requiring a new Creation by God to repopulate the planet. When one asks someone a question such as "Are you open to new ideas," most people interpret the question in ways that fit their own particular values and biases. We are all open to some things. What we want to understand is how do birth order and other influences on personality channel our predispositions to be open to experience in specific ways. Personality tests are not particularly good at capturing these context-sensitive effects.

In Born to Rebel I was careful to identify the social and intellect context of each the innovations I was studying. For each scientific revolution that I studied, I operationalized the social context in terms of how ideologically radical the innovation was, how long the revolution took to be resolved, and various other measures of "radicalism." These markers of controversiality proved to be excellent predictors of the size of birth order effects. In addition, these contextual markers were also significant predictors of the effectiveness of other explanatory constructs, such as age, parent-offspring conflict, and social attitudes. In my book, I was continually dealing with person-by-situation interaction effects. Psychologists are now trying to replicate my findings without worrying about the context. Another problem with such studies is that self-report data tend to yield fairly small birth-order effects. We know from considerations of statistical power that one needs a sample of between 500 and 1,000 individuals to be reasonably sure that one is not missing a true effect owing to sampling error. The average study in psychology involves about 250 individuals. Psychologists have been designing studies to test my claims, based on samples of 200-400 subjects. These studies are generally incapable of answering the question that the investigators are asking, which is a waste of time and effort. Unfortunately, most psychologists—to this day—do not appreciate the issue of statistical power.

I recently designed a study myself to get around these dual problems of statistical power and self-report biases. The sample already includes about 3,500 subjects, and some of the questions I have asked are aimed at tapping objective indicators of behavior. For example, if I ask individuals to tell me how empathetic they are, using a 9-step scale, I know that I am not always going to get a realistic self-appraisal. In addition, most people don't know where they really lie on an objective measure of empathy. They might know that they are higher than the average person, but they do not know whether they are in the 60th percentile or the 70th percentile—we don't go around wearing "empathy badges" that identify us like men and women. And so there's a lot of imprecision in answers to questions of this sort. Small effects, including those for birth order and other aspects of family dynamics, are easily missed. So what I have done in my study is to include a second set of questions, which ask respondents to rate themselves relative to their friends, spouses, and siblings. Consider the approach entailed in a direct sibling comparison. We generally know (or think we know) whether we're higher or lower than a sibling on most personality traits, and so the method of direct sibling comparison serves to anchor each personality scale with a concrete comparison. We might be in error as to where we place ourselves on such scales-in absolute terms-but we are probably close to the truth in assessing the relative difference between ourselves and a sibling. When people compare themselves with a sibling, it turns out that the correlations between birth order and personality are at least twice as large compared with when subjects assesses themselves without reference to anyone else.

JB: You're talking about statistical results, but a lot of people are reading your book and thinking about it on the personal level.

SULLOWAY: Well these two ways of viewing the matter are not inconsistent. I employ statistical techniques and large samples just to be sure that I am right about the relationships I am studying. Once a researcher obtains the correct answer by this method, findings can be illustrated by anecdotes, which represent the level of personal truth that lay readers seek in a book such as mine. Anecdotes have a wonderful power to convey emotional truths. But I do not consider anecdotal evidence to be a proof of anything-on this important point I depart company with most historians, who actually think they've proven something when they tell a story. A story proves nothing; it just demonstrates that people have been clever enough to find evidence to fit their hypotheses. The approach I took in Born to Rebel involved testing my hypotheses using large statistical samples, and then illustrating the various relationships I had documented by telling one or more stories that brought these relationships to life. For example, laterborns are more likely to challenge the status quo, and they are more likely to cause their parents aggravation by doing all sorts of outrageous things. A person who exemplifies this tendency is Voltaire—he got his start as a poet when his family, to amuse themselves, had Voltaire and his elder brother Armand engage in poetry contests. The family soon discovered that Voltaire was a terror at satirical poetry—and he was probably aiming many of his scathing ditties at his elder brother, whom he didn't particularly like. The family put an end to these poetry contests. The father subsequently became concerned that his younger son would end up wasting his life in such an unfruitful profession as literature. "You will starve to death," he warned his son. But a poet had been born, and Voltaire became the richest literary figure in all of eighteenth-century Europe through the sales of his ribald poems, plays, and books. His brother Armand, by the way, became a religious fanatic. What is Voltaire most famous for? His scathing critiques of the Catholic church!

Here is another story about Voltaire that I cannot resist telling. Voltaire once witnessed his father having a vehement argument with his gardener. Voltaire's father was a stubborn man. He finally dismissed the gardener, saying to him, "I hope you find an employer who is as gracious and kind as I am." Voltaire thought this remark was ridiculous-that his father, one of the most irascible people he knew, would tell the employee he had just fired that he would be lucky to find another employer as even-tempered as himself. Soon after, Voltaire went to see a play. It turned out that there was a scene in the play just like the Voltaire had witnessed between his father and the gardener. After the play was over, Voltaire went to see the playwright and asked him if he would substitute, in the next performance of the play, a few words that were closer to his father's own remarks. Voltaire then went home and invited his father to attend the play. His father accepted, and as the father sat through the play, there finally came the scene with the gardener. Voltaire wrote of this episode that "My good father was rather mortified." This story reflects the use of the satirical knife blade, and the turning it in his victim, that Voltaire did to his enemies throughout his career. Some noblemen became so outraged by Voltaire's satirical broadsides that they had him beaten, or arranged for him to have a nice long stay in the Bastille. In any event, these are the kinds of biographical stories that bring a figure like Voltaire alive; and they also illustrates the kinds of unconventional and irreverent qualities that younger siblings have displayed throughout history.

JB: How has your own birth order affected your personality and your life?

SULLOWAY: I was the third of four boys, but I'm a functional youngest child because my brother Brook is nine years younger than I am (and from a second marriage). For nine years, I therefore grew up without a younger sibling, and I do not think that Brook had much of an influence on my personality. But my two older brothers did have an influence on me; we were each about two and a half years apart, and there was a lot of fighting among us. I think I have a pretty typical laterborn set of personality characteristics. As someone who has existed as an academic for more than two decades without ever holding a formal job, I have had an unconventional career.

JB: Are you familiar with Judith Harris's work on nurture?

SULLOWAY: Yes, she has focused on the influence that peer groups have on children. In response to the findings by behavioral geneticists that most environmental influences are not shared by family members, she and a few other psychologists have argued that the family has only limited influence on personality. An alternative viewpoint, to which I subscribe, is that families do not represent a shared environment. Hence they influence siblings in different ways, which is not the same thing as having no influence. I believe that Harris is correct to emphasize the importance of peer groups, but she is too single-minded when she denies the importance of systematic within-family differences. Actually, the two approaches (family niche theory and peer group influences) overlap in important ways. For example, some family members are probably influenced by their peer groups more than others, and we would especially expect this to be the case for younger siblings because they are more open to experience. It appears that middle children, in particular, are the most closely identified with peer groups rather than with the family. One can perform a very simple test of this claim, as Catherine Salmon did in a recent doctoral dissertation at McMaster University. One asks people to respond 10 times to the question "Who am I?" Middle children are significantly less likely than firstborns or lastborns to answer "I am a Brockman" or "I am a Sulloway"—that is, middle children do not identify themselves by using the family label. Why is this? From a Darwinian point of view, we know that middle children are at a disadvantage—they don't have the benefit of being first, which leads to greater parental investment because firstborns are closer to the age of reproduction. The lastborn has the benefit of being the last child the parents are going to have, so parents will tend to invest heavily in this child so that it will not die in childhood. The offspring who tend to get lost in the shuffle are middle children. How do they respond? They become peer oriented. If a person is not favored within the family, it is a wise strategy to build one's bridges to other sources of support.

JB: What conclusions will a father or mother take away from your book with regard to the raising of their children?

SULLOWAY: I do not directly address the issue of childrearing in my book, although any reader can draw numerous relevant conclusions on this subject. This is an issue, however, that I do discuss in public lectures. One obvious implication of my researches is that sibling rivalry is not pathological. Many people feel that if rivalry exists among offspring, the parents must have done something wrong. This is mistaken: sibling rivalry predates the dinosaurs. Sibling competition shapes creative behavior—it's part of the process by which children sharpen their endearing little claws and get ready for life. It is a considerable relief for parents to understand this point. Secondly, parents need to understand why siblings engage in rivalry—such competition is part of the effort to feel special within the family, to feel that one is not discriminated against. Ultimately, sibling competition is all about optimizing parental investment. What each sibling wants is special time with each parent, and when parents provide such moments, it makes children happy. In fact, this is a useful bit of practical information, if parents have not already discovered it. By being different, each sibling is trying to develop a special set of interests, a special niche, causing parents to pay attention to them and to them alone.