JB: What sort of grant support did you have?

SULLOWAY: My collaboration with my 110 expert raters was done when I was a MacArthur Fellow, and this fellowship was a opportune source of support for my project. Being a MacArthur Fellow was a boon to my ability to get on with the massive amounts of empirical research for this project and to overcome one of the most obvious objections to it, namely: If I have selected the historical samples, why should anyone trust my results? It was essential that the classification of my historical participants as supporters or opponents of radical change be done by people other than myself. As a MacArthur Fellow, I spent every penny of my stipend on research and living expenses.

JB: What procedures did you use after you gathered the results?

SULLOWAY: After I had assembled my samples for each of the 121 historical events in my study, I coded every individual for up to 256 different background variables. One of the most unusual features about Born to Rebel is that it surveys more than a hundred potential causes of radical thinking, and attempts to rank order these influences in terms of overall influence. Is social class a good predictor of radicalism? This variable is in my data base, so I can answer this question: Social class is not a good predictor. Is age a good predictor?: Yes, age is, just as Max Planck and others have thought, although age is not as good a predictor as either social attitudes or birth order. I also tested a special sub-set of variables-those related to sibling strategies and family dynamics-many of which also turned out to be significant predictors of radicalism. For example, age spacing between siblings is a significant predictor: Large age gaps between brothers and sisters cause the effects of birth order to dissipate. Conflict with parents is also a significant predictor of radicalism, and it is especially important for firstborns. Laterborns do not need to have the Wicked Witch of the West as a mother in order to become radicals: They have their older siblings to induce this behavioral predilection. But firstborns who grow up in happy families typically identify with parents and authority. Significant conflict with a parent tends to undermine this pattern of identification and causes firstborns to identify instead with the underdog. When I tested all of these different variables simultaneously, the single best predictor of radicalism proved to be birth order. But birth order is hardly the only significant predictor. The next two predictors in importance are social attitudes and age, followed by parent-offspring conflict.

JB: Your sampling of participants in radical revolutions seems to involve highly accomplished people who were successful enough to become historical figures. Would the same results apply if you had included the average person in your samples?

SULLOWAY: There are two ways we can answer this question. The first is to take my sample of 6,500 historical figures and rank them on a scale of eminence. I have done this, using 18 different eminence measures. There are some people, such as Darwin and Newton, who are particularly eminent. But when we go down the list, in order of eminence, we come to people who are so obscure that even Newton or Darwin scholars have not always heard of them. After we have stratified individuals by eminence, the question we may ask is whether there is any dilution of a general birth-order effect as we go up or down the scale? In other words, are larger effects are associated with eminence? As it turns out, the most obscure people in my sample show virtually the same effects for the influence of birth order as do the most eminent people. It is true that I have not included individuals in my study who are so obscure there is no biographical information about them. But by extrapolation, if there are biases in my study owing to the selection of eminent figures, we should be able to detect their extent when the samples have been stratified by eminence.

The second way to tackle this problem is to study ordinary people. Fortunately, this research has already been done. As I have previously mentioned, there are more than 2,000 published studies on birth order. Much of my own contribution in Born to Rebel was to try to make sense out of this extensive literature. This literature has been repeatedly criticized because many of the studies are not well designed or controlled for important background variables. The simplest way to solve these problems is to throw away all the studies that are not well designed. If we take the remaining 196 studies that are controlled for class and sibship size, we may ask how many significant findings are there in this set of 196 studies. As it turns out, there are 86 significant findings. The key question, then, is how often would this number of significant findings occur by chance? The procedure used to answer this question is called meta-analysis. The answer is that we would expect to get 86 significant results by chance once in a billion times. In fact, the birth-order literature is in surprisingly good shape compared to most other research areas in psychology.

JB: Let's talk about the intellectual antecedents.

SULLOWAY: There is a vast literature on birth order and personality, and, of course, on many of the other variables that I studied in Born to Rebel, including gender and parent-offspring conflict. Freud, for example, based his theory of personality development on parent-offspring conflict, and most aspects of family dynamics that I studied have also been extensively studied by other people. In my opinion, one of the most useful contributions of Born to Rebel was my effort to simultaneously assess many different influences that theorists from Freud to the present have thought were important.

JB: Two questions—What about the only child, and what about women? It seems like all the example I've heard you talking about are males.

SULLOWAY: I included a chapter in my book on women. In this connection I made a special effort to find historical samples where a substantial proportion of women participated in radical events—precisely so I could say something substantive about sex (and sexual differences). In general, women who end up in the history books as supporters of radical causes tend to be an unusual group. To begin with, they are much more liberal than the average man in the population. They are also more likely to have experienced substantial conflict with a parent, and they are far more likely to have been laterborn (and usually lastborn). In other words, the women who made it into the history books are typically the rebels of the family. These are individuals who boldly transgressed into a man's world because they were not willing to sit there and do what women were generally supposed to do prior to the 20th century. Their first "revolution" was getting into my sample. The historical revolution they later participated in, and that brought them to my attention, was a second revolution for them. Because I possess a reasonably large proportion of women in certain radical movements in my study—for example, in the Protestant Reformation and in 61 social reform movements that I studied in American history—I can say with confidence that birth-order effects in radical temperament hold for women as well as men.

Only children pose another interesting question. I view only children as the ideal controlled experiment. They are what it is like to have no birth-order effects at all: Only children have no siblings, hence they have no sibling rivalry. Two predictions follow from these circumstances. One is that only children ought to be intermediate on many personality traits. This follows because they are not being pushed by a younger sibling into being particularly conscientious or aggressive; and they are not being pushed by an elder sibling into being particularly daring or unconventional. Hence only children ought to be somewhere in the behavioral middle. And this is where they turn out to be. Secondly, only children are free to occupy any niche they wish to in childhood—for example, they do not have to worry about who is going to move in to occupy a niche that they vacate. For this reason, they are free to roam around. As a result, they ought to be more variable than average in their personality traits and interests, and they are. Only children are the most unpredictable group. Their behavior is difficult to predict precisely because their childhood options are greater than for people who grow up with siblings.

JB: What were some of the reactions to your book?

SULLOWAY: There have been a variety of reactions to the book, some that I anticipated and some that I did not. One of the most surprising reactions involved the accusation that I was a "determinist". This accusation took two forms: one involving determinism in a general sense and the other involving genetic determinism. I was puzzled by both forms of this accusation. If one reads my book carefully, it is obvious that sibling strategies are not strictly "determined". Rather, they are self-determined. Individuals have considerable choice as to which strategies they adopt in family life. For example, younger siblings are—on average—less aggressive than their elder siblings, but younger siblings always have the option of being aggressive. Nothing stops them from punching an older sibling in the nose. But such aggressive acts are generally ill-considered, because older siblings can punch back harder. Younger siblings learn this lesson early on and behave accordingly. Most of the choices that siblings make in the course of human development are voluntary. Hence these choices are self-determined. It's really a mincing of words to call such actions "determined". We all know that it is unwise to cross the street when a giant Mack truck is likely to run us over. This fact, to which most of us wisely adapt, does not mean that all of our actions are predetermined. In short, some things in life are determined, and other things are not; but I hardly see this circumstance as something to get worked up about.

JB: You're talking about probabilities, you're not claiming that every firstborn has these characteristics.

SULLOWAY: Right, mine is a "probabilistic" account of behavior, in part because there are so many different variables that influence personality, including gender, parent-offspring conflict, birth order, and lots more that I document in my book. One can legitimately accuse me of being a multi-determinist. My book tells a very complex story and, in this story, there is lots of room for individual choices.

The second form of the determinist accusation directed against my book involved attempts to portray me as a genetic determinist. The few reviewers who tried to make this point did not understand the difference between a purely genetic argument and a developmental one. It is true that Born to Rebel is very much a Darwinian book, but this is hardly the same as being an argument for genetic determinism. One of the most subtle features of my argument in Born to Rebel is that one can propose a Darwinian argument that is highly environmentalist. Normally we don't hear about these kinds of arguments because this aspect of the story of human development is not well understood.

Here's the argument in a nutshell. Based on Darwinian theory, I argue that offspring are predisposed (genetically) to compete for parental investment. The role of the environment inevitably comes in because individuals—based on the contingencies of birth order, gender, and age spacing—tend to occupy different family niches. This part of the argument is not at all based on genetic determinism. There are no genes for being firstborn or genes for being laterborn. Siblings become very different in large part because different family environments—or niches, if you will—lead them to adopt differing strategies in their efforts to get out of childhood alive. Because firstborns are bigger than their younger siblings, it is easier for them to employ aggressive and tough-minded tactics, which then become part of their personality. This part of the theory is very much an environmental and interactionist argument. My reasoning in Born to Rebel is like Pinker's argument in The Language Instinct. There's undoubtedly a hard-wired capacity for humans to engage in verbal communication, a capacity that other apes do not possess. But the country we grow up in determines which language we learn to speak. In the same way, we are hard-wired in a Darwinian sense to compete with our siblings for parental investment, but the particular aspects of each person's personality are the product of characteristics of the family environment in which one grows up, just as speaking German in one country, and French in another country, are appropriate linguistic differences produced by the same language instinct. In short, my argument is not just about nature; nor is it just about nurture-it is a combined nature/nurture argument, in which much of the psychological details are clearly on the environmental side.

Most readers of my book correctly understood this point. In an interview with Ted Koppel on "Nightline", Stephen Jay Gould emphasized this general logic when he said that birth order provides one of the best demonstrations of the power of the environment and is, on this account, a wonderful antidote to the kinds of genetic determinist arguments espoused in "The Bell Curve". I find it ironic to have been accused of being a genetic determinist by some people, and yet to have been publicly defended against this accusation by one of the leading critics of such views.

JB: Interesting that Gould and Pinker, who frequently disagree, appear to support your ideas. What do the adaptationists—John Maynard Smith, George Williams, Richard Dawkins—have to say about your book?

SULLOWAY: I don't know what Maynard Smith or George Williams think. I gave a lecture on my ideas at the Human Behavior and Evolution Society in 1995, where Richard Dawkins was the keynote speaker, and he seems to have been impressed with the argument. He referred to my paper several times in his keynote speech, at the end of the conference.

JB: What about Dan Dennett?

SULLOWAY: After the publication of Born to Rebel, Dan sent me a cordial letter saying that he had read my book and that, in general, he agreed with my argument. I am not surprised because, for a sophisticated Darwinian such as Dennett, there is not much that is really controversial about the book. It makes good sense that, if offspring are competing for parental investment, they will devise strategies to implement this competition in their favor.