.Sibling Rivalry

The Revolution Begins at Home

Five years ago, in his book Born to Rebel, Berkeley science historian Frank Sulloway presented some intriguing findings about the relation between personality and birth order within the family. Over the course of 26 years of research, Sulloway found that in pivotal historical moments of socially significant revolutionary change, whether in science, politics, or religion, laterborns were far more likely to favor change, and firstborns far more likely to resist it. Looking at the history of the West, laterborns were 18 times more likely than firstborns to champion radical political revolutions, 48 times more likely to suffer martyrdom in the Protestant Reformation, and 17 times more likely to support radical scientific revolutions during their early stages when the scientific evidence was not yet definitive. And among pre-Darwinian scientists, laterborns were 124 times as likely to support radical innovations.

At least in the West, major revolutions of social import bring out certain aspects of personality that strongly correlate with birth order. Taking his cue from Darwin, Sulloway argued that children come into the world desperately seeking the love and care of their parents–and that firstborns and laterborns find themselves in dramatically different situations in terms of seeking that care. To understand the sources of the roughly fifty percent of personality not governed by genetic influences, Sulloway argues, we must think less in terms of traits and more in terms of family survival strategies that later become enduring features of personality.

Laterborns enter their families as second-class citizens, lacking the rights of their more powerful older siblings, who are bigger, know more, and have already begun to fill up niches to gain parental approval. Laterborns are motivated to struggle for better rights and more power; they oppose the status quo and must find a niche that is not already taken by older siblings. Firstborns, by contrast, have an interest in maintaining the status quo and maintaining the parental investment that their younger siblings threaten; they are more identified with their parents, sometimes acting as surrogate parents to their younger siblings.

In fact, Sulloway found that firstborns who support radical change are likely to have experienced substantial conflict with their parents.

Firstborns have less of a struggle to find a family niche, and their superior size makes physical aggression and assertiveness a more functional strategy. Laterborns must engage in more agreeable manipulations to gain power; on average, Sulloway found that laterborns are more open to experience, less conscientious, more agreeable, and more extroverted than firstborns.

In the wake of Born to Rebel, personality psychologists claim that Sulloway vastly overstates his case. They note that when subjects are asked to describe themselves, birth-order differences are small. Sulloway retorts that if individuals are measured alone on personality traits, without sufficient attention to the behavioral context, birth-order differences are indeed small. But if researchers ask subjects to compare themselves with their siblings on the same traits, birth-order differences in personality come through loud and clear.

Now 54, Sulloway (a laterborn) is something of a maverick in academic circles. He graduated summa cum laude from Harvard and was chosen to be a member of Harvard’s Society of Fellows, a coveted position that frees promising students to pursue their own interests. Since receiving his PhD in the history of science from Harvard in 1978, Sulloway has remained on the edge of academia, working from grants and fellowships. The recipient of many awards, including MacArthur and Guggenheim fellowships, he spent most of the ’90s affiliated with MIT’s Program in Science, Technology, and Society, and is currently a visiting professor at UC Berkeley’s Institute of Personality and Social Research, where he teaches a course on evolutionary psychology. We met for the interview at his office in the Berkeley psychology department.

Timothy Beneke: What was the reaction to your book?

Frank Sulloway: The major critiques came from those researchers in personality psychology who had worked on birth order using surveys in which the subjects self-report. When subjects fill out the surveys themselves, birth-order differences seem considerably smaller than they are with historical samples, or with life stories of contemporary individuals.

So there was a battle line set up with some psychologists effectively saying, “When we go and measure birth-order effects using self-report, we don’t find much, and yet you have made all these impressive empirical claims.” I became very interested in trying to figure out what was going on, so I began designing surveys of my own. The first point I realized is that there are more than 2,000 studies already published on birth order, so it was pointless to duplicate research that had already been done. Instead, we needed to ask what might have been missed in the previous research. One pertinent observation that struck me about asking people to describe themselves on self-report personality tests is that generally there is no effort to compare the person with his or her own siblings.

So I designed a series of surveys where I asked people to rate themselves and a sibling. When you do that, you obtain all the personality differences that I had both posited and documented in my book. So, within families, siblings definitely judge the firstborn to be more conscientious than the laterborn. The firstborn generally occupies a niche as a surrogate parent; and that niche, and its associated strategies, is reflected in firstborns being more responsible, organized, self-disciplined, and so forth. Laterborns, who have less power, are seen by themselves and their older siblings as employing more agreeable, low-power strategies, so they score higher on traits related to agreeableness. Laterborns also score higher in openness to experience. In my book, I posited that firstborns are more open in the sense of being intellectual or smart, but laterborns are more open in the sense of being untraditional. These two differences show up in within-family comparisons. Finally, laterborns are seen as being more extroverted in the sense of being sociable, fun-loving, and gregarious. By contrast, firstborns are seen as being more extroverted in the sense of being assertive or dominant–traits that relate back to their greater size and power within the family.

A study was recently conducted in which siblings were asked to determine who is the rebel in the family and who is the scholar. Firstborns were described as the scholars of the family and laterborns were characterized as the rebels. Similar data that I have collected since my book was published encompass information on more than 200,000 subjects. These data clearly show that laterborns, relative to firstborns, are judged to be more unconventional, more untraditional, more rebellious, and more likely to endorse a radical revolution.

I am one of the 200,000 people who took the personality measure on your Web site at www.sulloway.org. I remember thinking: This is only a measure of self-representation, and how people think about themselves at a given moment in a somewhat ungrounded, abstract way. What I take more seriously are correlations between birth order and actual behavior, something you document very powerfully in your book.

My own reaction to most self-report data is exactly the same as yours, except that I feel that if I can document birth-order effects and other related effects with this kind of self-report information, then the real effects in the real world are probably bigger than those I am able to document. Remember, I was trying to see if there were any birth-order effects at all. Numerous psychologists say there are no effects worth mentioning. Yet when we measure birth-order differences within the family by asking people to compare themselves with their siblings, the effects are even larger than gender differences. If you have found anything bigger than a gender effect in personality research, you have really done well.

Let’s assume you’re right about the correlation between birth order and certain aspects of personality. Isn’t there still something of a leap in explaining these differences in terms of family niches?

Yes, but only a small leap. Some of these explanations are already documented in the birth-order literature. For example, there are many studies showing that firstborns are more parent-identified than laterborns. So when I set forth the argument that firstborns tend to support power and authority because they are more identified with parents, this argument was not all that dependent on a leap of faith. I also argued that surrogate parenting leads firstborns to be more parent-identified and responsible–that may be a bit of a leap.

In addition, when I argued that laterborns, and middle children in particular, are the peacemakers of the family and are more likely–like Martin Luther King Jr.–to adopt nonviolent methods of protest, that has been studied in the past and has also been replicated since the publication of my book. In particular, if one asks within a family who is the peacemaker, it’s usually the middle child.

In recent research I have conducted, I have been able to ask certain questions I could not ask in historical research. I can ask, for example, to what extent a subject acted as a surrogate parent toward younger siblings. Similarly, I can ask subjects how much they bossed their siblings around. Answers to these questions are related to both high conscientiousness (for surrogate parenting) and to low agreeableness (for bossiness). I therefore have documented the expected relationship that firstborns generally act as surrogate parents and that they also generally act in a bossy manner. So there is considerably less of a conceptual leap between the psychological mechanisms, which I mostly had to posit in the book, and what we know today about those behavioral relationships.

I don’t actually think the theory of the psychological mechanisms lying behind these personality differences is that controversial. I think there are other matters, however, that have remained controversial. The most controversial of these is the difference between birth order effects as measured within the family, using direct sibling comparisons, and birth-order effects measured when one does not compare oneself to a sibling. It turns out that if one asks people to rate themselves–say, a laterborn–with a best friend who is a firstborn, one obtains much smaller effects than if the person were compared with his eldest brother. The effects with nonfamily members are about one-third or one-half as large as the birth-order effects one obtains if one asks people to compare themselves with their siblings.

So we have a puzzle. I have documented numerous birth-order effects in history which involve extrafamilial data. But birth-order effects outside the family, at least in contemporary personality data, are considerably smaller than within the family, so we have a bit of a contradiction. The resolution of this inconsistency lies, I think, in the fact that radical revolutions in history foster conflicts in society that generally stay within the family. Many radical revolutions have even involved, in explicit ways, the language of family dynamics. In the French Revolution, the King was the “father” of the country and the citizens were his “children.” The revolutionaries saw themselves as “brothers” and “sisters,” and they found themselves in conflict, just like brothers, over the need for filial loyalty and the kinds of tactics appropriate to contesting such loyalty.

So in times of radical revolution in history, there is an opportunity for within-family dynamics to become, temporarily, societywide dynamics. This would explain why one can often document larger birth-order effects in historical data than one can with self-report personality data that do not involve direct sibling comparisons.

There is research suggesting that parents, and mothers in particular, tend to act more anxious and possessive toward their first child than toward their second or later children. They are more clingy and overprotective, and they try to keep the child physically closer to them. Obviously, having a first child is a very different experience than having a second or third child. Couldn’t this influence personality?

There have been studies suggesting that new parents are more anxious parents, as you say. That may or may not have an influence on personality; it would be surprising if it didn’t have some influence. The question is: how much?

I examined the eldest children of people who had married spouses who already had previous children, so these biological firstborns grew up as functional laterborns. I found that these biological firstborns tended to act more like laterborns in history. I couldn’t find any difference between them and true laterborns.

So my own feeling is that there are probably some consequences of differences in parental behavior toward children of differing birth ranks, but such psychological differences may not necessarily affect radicalism. Having an anxious, controlling parent might make a difference in terms of how exploratory such children are, but exploratoriness and radicalism are not the same things.

“Exploratoriness” sounds a lot like openness to experience, which, you claim, is greater in laterborns.

Yes, but remember I said that openness to experience has two very different elements to it. There is an intellectual element at which firstborns excel–they obtain higher IQ and SAT scores, for example. Openness to experience is a broad term; it all depends on what kind of openness we’re talking about. As long as it is openness within the system, firstborns have an advantage. When we consider the laterborn component of openness–namely, unconventionality–it is a subset of what we are talking about in terms of openness more generally. Firstborns are, by the way, overrepresented in “intellectual” kinds of revolutions; this finding is consistent with the extensive data on firstborn intellectual superiority. Laterborns excel in one subcomponent of openness–namely, radicalism and rebelliousness–and that is why I was very careful to define what I meant by a “radical” revolution. I meant a revolution that is socially, politically, and religiously radical, and that is why I used 110 expert raters to operationalize exactly what that meant.

A radical revolution is something that the Pope generally doesn’t like. By contrast, a conservative revolution is something the Pope does like. A technical revolution, in which firstborns would also likely excel, is something the Pope generally doesn’t understand and, for this reason, neither likes nor dislikes. There is a chart in my book in the last chapter that plots 28 major scientific controversies in terms of where they lie on a social ideology spectrum and then indicates what kind of birth-order effects one obtains in each case. The chart nicely supports the point I have been making here and shows just how context-sensitive birth-order effects are.

It seems to me that the American Psychological Association should mandate that the birth order of subjects be given as part of the information in all psychological research. For instance, [UC Berkeley psychologist] Robert Levenson has developed an objective measure of empathy, defined as having the ability to know what others are feeling. I would be very curious to know if there are differences in objective measures of empathy and birth order. You would presumably predict that firstborns would be less empathetic.

Yes, and there are several studies showing just that. But this whole line of research needs to be interpreted correctly. The argument is not that firstborns lack empathy. Every firstborn has learned to be empathetic under some circumstance. The question is: what portion of a person’s time and energy do they spend being empathetic under particular circumstances? Laterborns, for example, are more fun-loving than firstborns, but that doesn’t mean firstborns can’t laugh at a good joke. Everyone is capable of expressing these same traits. But one needs to reconceive traits as “strategies,” and then to understand that there is a preference for certain kinds of strategies over others by birth order, and that these sometimes subtle preferences will only be elicited in public under certain limited circumstances–for example, when they are appropriate, and when the context is right for a successful behavioral outcome.

I like to remind people that Robespierre was a pretty nice guy before the French Revolution broke out. It took the French Revolution to turn Robespierre into a leader of the Reign of Terror.

Your research suggests certain obvious questions. Will China’s one-child policy have a political effect on the future of China, solely as a result of birth-order effects?

It will have some effect, but not much. The consequences of one-child families are counterintuitive. As countries go from having large families down to just one or two offspring per family, the offspring that are lost are all middleborns. There is always a first and a last child, and middleborns are in between them on most measures of radicalism. So, on radicalism at least, the mean of the sample doesn’t change much when sibship size declines from six to two. When sibship size finally declines from two to one, it is not that we go from a world half-filled with laterborns to one exclusively filled with firstborns. Rather, we now find ourselves in a world of only children, and only children, like middleborns, are intermediate in most personality characteristics between firstborns and laterborns; in their attitudes toward revolutionary changes, only children are a little more like firstborns than laterborns, but they are not identical. So, as sibship size declines from two children to one, the population for radical inclinations becomes lowered only slightly. Still, radical revolutions do depend on population differences, so it is conceivable that such demographic changes could exert a small but meaningful effect.

Is there a relation between birth order and crime rates?

There appear to be too many influences going in different directions when we consider the possible relationship between crime rate and birth order. Firstborns are more tough-minded than laterborns, so they might be more inclined toward violent crime, but they are also more socially conventional, so they are probably less likely to get involved in crime at all. Hence I would not want to offer a prediction about birth order and criminal behavior. Perhaps there is a relationship between birth order and types of criminal behavior. There is some evidence that laterborns are more likely to be involved in delinquency, but that is a phenomenon that appears to be associated with lower-class families being larger, with more laterborns. So again, I don’t think there is much of a relationship between crime and birth order.

What about birth order and voting behavior?

The current data on this subject are mixed. Several different studies using historical samples–for example, US Supreme Court voting–indicate that laterborns tend to vote in a more liberal direction than firstborns. By comparison, a big study a couple of years ago showed no differences in political attitudes in a sample of about 1,200 subjects. Still, this particular survey did not ask the respondents to compare themselves with their siblings, so we really don’t know what the within-family results would have been.

With a colleague, Michael Shermer, I collected another large sample on religiosity, and we found small but significant differences in religiosity and political views when measured within the family. In another sample of more than 20,000 subjects whom I surveyed using the Internet, I found a consistent tendency for laterborns to report being more unconventional and untraditional than older siblings. It should be kept in mind that the differences I obtained in political attitudes in my book were not that big. Much more impressive differences show up when we ask: Given the political attitudes people hold, how likely are they to endorse a new way of thinking?

Let’s shift ground a bit. Some people don’t want to believe that their receptivity to radical change has to do with something as arbitrary as birth order. People feel that their sense of free will has been affronted.

I think this is a pseudo-issue on two fronts. First, these behavioral phenomena are not really “deterministic”; they are self-deterministic. Laterborns are more likely to use low-power strategies within the family, but they have a choice, and they learn to exercise the optimum strategy by first punching their elder sibling, for example, and learning that their elder sibling can punch back harder, so they soon come to the conclusion that this is a stupid strategy. And they learn to perfect a variety of low-power strategies, including the use of humor. In other words the subject is an active agent in the development of these strategies. Are such behaviors strictly determined or are they self-determined via strategic choices?

But it’s not you who determines the self-determination; it’s a birth-ordered situation over which you have no control.

We do have some choices. It is not as if we are all completely passive vehicles in some massively deterministic plot.

But a second, more important point in response to your question involves understanding effect sizes. No one is saying that birth order accounts for 100 percent of the variance in human behavior. It is just one of those many variables that add one or two or three percent to the explained variance in behavior in specific contexts. This means there are lots of other considerations influencing human behavior and, in many cases, supplementing or overriding birth-order differences. Some people seem to be alarmed by the idea that birth order may influence whether one endorses a radical revolution, for example. But, ironically, they do not seem to be alarmed by the notion that gender has an influence on levels of aggressivity or physical violence, or that social class “determines” educational levels. Similarly, people don’t get upset about the idea that very religious people are more likely to endorse conservative causes. That influence is much bigger than any known birth-order effect. So, in essence, some people are bothered by the small amount of the variance in behavior that is explained by birth order, but are not bothered at all by other equally “deterministic” influences.

But you’re giving us one more thing to be upset about.

Right, but it seems reasonable for me to expect consistency from the people who express such views. If someone is upset about this moderate player in the game of understanding human behavior, then they ought to be much more upset by other equally “deterministic” influences that they take for granted.

Still, in specific contexts you claim that the effect of birth order is quite strong. You write: “During major revolutions choices between the old and new order can almost always be traced to differences in family niches.” The idea that I would support or not support a revolution because of my birth order is a little hard to swallow.

One needs to be careful here. I am saying that one can almost always trace some influence in major revolutions to family niches–I am not saying family niches are therefore the only element of the story that we need to know about. Hence, I am not saying that family niches are the only cause of individual references in radicalism. I am just saying that there appears to be a consistent link.

To understand Born to Rebel, one needs to recognize that it is really two books in one, with the second book being represented by several hundred pages of notes and appendices. In one of these appendices, I provide information about the relative importance of ten variables that were significant in predicting attitudes toward evolution from 1700 to 1875–the best predictor of the lot of attitudes toward that revolution was religiosity. Birth order was the second-best predictor. Other significant predictors included being young. National origins also played a role, as did parent-offspring conflict. What I provide, then, is documentation of a multivariate model in which birth order is just one of many relevant influences on scientific radicalism. It is true that when we examine radical revolutions, they generally do appear to tap within-family differences that I explain, in part, as the product of sibling strategies. In addition, the more radical the revolution, the more likely we are to observe this behavioral link. Still, birth order never acts alone.

A lot of people feel a lot of guilt at the way they treated their siblings when they were children. I wince when I think of the way I verbally taunted and tried to manipulate my older brother. You encourage people to see this process in terms of natural Darwinian survival strategies.

It is important for people to realize that they are not the only ones who did a lot of sneaky, sometimes even nasty things to their siblings. Almost everybody’s sibling was responding right back with such competitive behaviors. It’s useful to realize that sibling rivalry and sibling competition are universal phenomena that we appear to be hardwired to experience, at least under certain circumstances, and that sibling competition was generally more of a life-and-death struggle in the past than it is today. Yet we are still hardwired today to act as if such competitive behavior might make a difference in who lives or dies and who is favored by parents, and so on. I believe that seeing this competitive process in evolutionary terms helps to depersonalize the animosity that was involved and allows people to transcend it. Of course, an evolutionary perspective doesn’t guarantee that siblings will be able to put their childhood conflicts behind them, but it does provide a window of insight to be able to realize, “Gee, my brother was sometimes a bastard, but perhaps it wasn’t all that personal after all.”

Older siblings tend to take advantage of physical dominance in their interactions with their juniors, and younger siblings, who can’t use physical force as effectively, often employ satire and wit in very cruel ways. Voltaire is a great example of someone who could cut his elder sibling to the quick with clever verbal retorts. And if the parents laugh at such satirical barbs, then the victimized sibling can’t really retaliate because the retort is perceived to be made in jest. In sibling competition, each sibling is trying to evolve, in his or her own niche space, those talents that are the most effective in sibling conflicts, and they sometimes use those talents–even purely verbal ones–like a knife blade.

But I want to emphasize that this kind of aggressivity is not necessarily true of every sibling relationship. One of the most interesting questions, about which there is little research, relates to sibling pairs that are remarkably harmonious.

In lectures on the topic of birth order I sometimes give out advice on how parents can make siblings less competitive. The advice I give is this: Siblings will compete over anything. If parents are really able to convince their offspring that they value cooperation, siblings will begin to compete over who is the most cooperative sibling. But this tactic by parents has to be genuine. If offspring think that parents are trying to pull the wool over their eyes, the tactic won’t work. But suppose the parents are Quakers who truly value nonviolence. Then siblings will pick up on the value system of the parents, and their behavior will feed into that system in a way that maximally rewards them for their nonviolent efforts. So you end up with a family of Gandhis.

In encouraging cooperation, parents can do things like reward jointly done tasks. If they give their kids $20 to mow the lawn, then they should give them $25 to do it together. Similarly, parents can allow their kids the chance to pick the next vacation spot that the family visits. But here’s the catch: The kids have to work together to organize the whole vacation, and if they cannot do so harmoniously, they lose the opportunity to go where they wanted to go.

I find research on birth-order effects interesting, but I don’t exactly know what to do with it.

There are not a lot of practical implications that come from this kind of research, but there are a few things of a practical nature. Let me first issue a warning by noting what is not practical. For example, I would not advise any business to hire or fire people based on birth order, primarily because the features of personality associated with birth order are very context-dependent. For instance, if one assumes that laterborns are more innovative than firstborns, one would naturally hire laterborns. But one needs to realize that laterborns are more innovative than firstborns only in a “radical” revolutionary sense and not in an “intellectual” or “technological” sense. Second, if one did hire a laterborn instead of a firstborn, it might not be clear that the future holds an impending revolution; it might require moving in a conservative direction. So this hiring strategy would entail another mistake.

This kind of biographical information can be useful–although infrequently so–when one knows exactly what one wants: for example, when presidents appoint justices to the Supreme Court. Presidents typically don’t want the best person for the court. Rather, they want the person who will best fulfill their particular vision, and only their particular vision about the future of the court. A study has been done of the birth orders of the 108 justices on the court from the beginning to the present. There is a strong correlation between Republican presidents appointing firstborns and Democrats appointing laterborns, for reasons that are fairly simple. The laterborn justices have been more liberal in their social policies and in their voting records. So if a president is trying to stack the court in any particular direction, then a knowledge of birth order is potentially useful. But in decisions about who to appoint or hire for a job, we would never want to do that. And we could also argue that we probably don’t want presidents to do that for the Supreme Court either.

From the perspective of past presidents, incidentally, there have been mistakes in Supreme Court appointments such as Earl Warren, who was a youngest sibling and a former Republican governor of California. One might predict that if someone is going to defect from their previous social ideology after one has put this person on the court, that it is more likely to be a laterborn. So one might question the wisdom of a Republican president appointing a seemingly conservative lastborn justice like Earl Warren. Eisenhower once confessed that the “biggest damn fool thing I ever did” was to appoint Earl Warren to the Supreme Court, because Warren dramatically changed his social views after he was appointed.

You do consulting with family businesses. Tell me what you do.

I have had considerable professional contact with people who are trained in the business world, and who have impeccable credentials. Because of this exposure I have learned that I am capable of doing the following: I can listen to people talk about family business problems, particularly if they are of a personal nature. And if I cannot provide good intuitive advice about how to resolve a given problem in a family business, I know to whom to send people for even better advice. So when I give lectures to family business groups I often offer to do free consulting, in large part because I enjoy doing it. In about half the cases, I have distance from the problem that the people I am trying to help don’t have, and often I know of similar problems and solutions in the family business literature, so I am able to provide my own two cents on what to do.

Here is a problem that was presented to me. A man consulted me about a business that he wanted to grow. His elder sibling held half ownership and was nearing retirement and so did not want to take any chances with further investment. The two brothers were at loggerheads. The younger sibling thought the business would go under if they did not do something about it. The older sibling, however, refused to believe him. The first thing that I said to the younger sibling was that he would never be able to convince his elder sibling to change his mind. I could virtually guarantee him that. So the best thing he could do was to get the brother to agree to have an outside consultant come in–a neutral party, so to speak. And he should let the elder brother pick the outside consultant, and let this person come in and evaluate the business in an objective and independent manner. Now, the final advice from this consultant might just sway the elder brother. It was clear to me that this was the way to go, and the younger brother–being too close to the problem himself–had never thought of that. If the two brothers had just continued to debate the matter among themselves, it would have remained a sibling conflict in which neither would give in to the other.

Often I am confronted by issues about succession in family businesses. The boss is running the company, and the person–usually a man–has a bunch of kids in the business, and he is agonizing about which of the kids he should select to take over the business. The boss feels that if he gives control to the eldest, he will alienate his younger children, but if he gives control to one of the younger siblings, he will alienate all the others. The classic way around this dilemma is to hire outside consultants to come in and sit down with each of the candidates. These consultants then interview all of the people in the business, asking what each of the candidates for succession is like, what their particular skills are, and so forth. The consultant then provides feedback to each of the candidates about his or her skills. Finally, the consultants bring all of the candidates together in a room to talk about what each has learned from the companywide feedback he or she has been given. One candidate might say, “I am not the best-liked person, but I am seen as being very good at technical and legal work.” And another might say that the employees look to him as a natural leader, but he also now recognizes certain weaknesses in his leadership style.

Through this kind of companywide feedback and open discussion, it generally becomes clear to everyone who the new CEO should be. Furthermore, it is not a solution imposed by the parents, and it is not imposed by the outside consulting firm either. Such consultants merely facilitate a flow of information that makes public what has previously been private. Almost always, there is a consensus as to who should actually take over, which gets around the problem of Mom or Dad dictating the business succession and destroying the family in the process.

One final question. As we experience less material deprivation, in the West at least, could it be that sibling competition is decreasing, so that birth-order niches are less powerful an influence on personality?

It could be. We don’t actually know if these effects are smaller today than they once were. This issue is tricky, because radical revolutions that seem to bring out many of these differences have become less and less frequent. It would appear that Western society has gone through most of the really major ones, and there are now no big revolutions left. We’ve moved the Earth from the center of the universe, and we’ve moved man from the center of creation. The big conceptual revolutions appear to be over, leaving us with understanding how substances such as DNA work and other typically technical questions. So we have not had any really good tests of these kinds of birth-order effects–at least those that relate to radicalism–since Freud and psychoanalysis. Major conceptual revolutions just don’t come along that often. The last big revolution in science was about plate tectonics and continental drift, and that was mostly a technical transformation, compared, say, with Darwinism.

Still, when I study the personalities of siblings within the family, I have been able to document birth-order effects that are as large as I ever expected to find. It is just that their transference to behavior outside the family appears to be modest in most self-report surveys.

Researcher Catherine Salmon recently conducted a study in which she asked people how likely they would be to support a radical theory such as cold fusion, and she actually obtained a birth-order effect that was as impressive as anything I have found in history. And Salmon didn’t even ask the best question–cold fusion does not involve radical ideological issues but rather purely technical ones.

It would be nice, of course, if another major revolution were to come along, so we could see if it brings out birth-order effects like those that have appeared during most radical revolutions in history. In the meantime, I have been designing various Internet surveys that assess behavior in varying contexts–such as dominance hierarchies at work–and this context-sensitive approach has yielded reasonably impressive birth-order effects. In my view, the key to obtaining birth-order effects outside the family is to reproduce, as closely as possible, the behavioral context in which the sibling strategies that underlie these effects originally developed. When one does that, the influence of birth order on adult behavior appears to be just as demonstrable as it was several centuries ago.


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