Thus, considering all these factors other than birth order greatly improves predictions about personality and revolutionary tendencies. But it also lets one recognize as even stronger the effect of birth order itself, because birth order’s effect interacts with that of the other variables, such as that of gender in the examples of the preceding paragraph. That is, the real effect of birth order is greater if it is considered in conjunction with other variables than if one considers it by itself.
Mr. Sulloway was originally drawn to studying birth order by a question concerning scientific creativity: Why are some scientists much more open-minded to radical innovation than other scientists who have better brains and opportunities? For example, what was it about Charles Darwin—a poor student, one of six children of upper-class landed gentry parents, and a graduate of what was then a conservative establishment, Cambridge University, where he went to study to become a minister—that led him to make the most radical advance in the history of biological thought? Why was Darwin the one to recognize evolution as a fact, when most other biologists of the day failed to reach the same conclusion? Darwin himself wondered about those questions:
I have been speculating last night what makes a man a discoverer of undiscovered things; and a most perplexing problem it is. Many men who are clever—much cleverer than the discoverers—never originate anything…. I have no great quickness of apprehension or wit which is so remarkable in some clever men, for instance Huxley.
Historians of science must not only ask who innovates but also who embraces or rejects someone else’s innovation. As the evidence for a scientific discovery gradually becomes overwhelming, most scientists eventually accept it regardless of their personality. But when a discovery is first claimed, the evidence may be inadequate even for a theory that finally does prove correct, continental drift being a recent example: it was proposed in 1912, but not widely accepted until the late 1960s. At that early stage, acceptance or rejection of a novel theory virtually serves as a test of one’s tendency to revolt or to conform. For example, I have a biologist friend whose penchant for embracing radical-sounding theories is especially transparent; he embraces even theories that he cannot possibly understand. What makes him and some others so eager to jump in whenever they sense a new view, right or wrong, battling with conventional beliefs?
To answer these questions, Mr. Sulloway has rated on a seven-point scale the views of 3,890 scientists who expressed support or rejection of twenty-eight significant scientific revolutions or innovations, ranging from Copernicus’s heliocentric theory, through Darwin’s theory of natural selection, Einstein’s theory of relativity, and Freudian psychoanalysis, to continental drift. Birth order proves to be a major factor: laterborns are twice as likely as firstborns to favor a scientific revolution before its results are generally accepted. But just as with personality, that modest difference conceals bigger effects apparent on further analysis. Scientific revolutions, in Sulloway’s survey, include radical ideological challenges to established religion and social values (e.g., the views of Copernicus and Darwin), theories with no ideological implications (such as glaciation), and reactionary theories lending ideological support to established values (e.g., eugenics). For radical theories, laterborns are five times more supportive than firstborns; for glaciation, birth order makes no difference; but firstborns are twice as supportive of reactionary theories as are laterborns.
Just as he did for personality, Mr. Sulloway examines the effect, on scientific radicalism, of many other factors besides birth order. That analysis provides new insight into why Darwin was the one to appreciate the fact of evolution, at a time when nearly all biologists were still convinced creationists. Darwin proves to have had an oversupply of factors destining him toward radicalism. He was lateborn (the fifth child) in a large family (six children), separated by a four-year gap from his next oldest sibling, affected by his mother’s death when he was eight and by a troubled relationship with his father. Not only was he a youngest son, but he was the youngest son of a youngest son going back four generations, while his mother’s father was the youngest of thirteen children. When all these factors are combined into a statistical model, one concludes that Darwin (and also his great contemporary Alfred Russel Wallace, the independent co-discoverer of evolution, like Darwin the fifth of six children and four years younger than his next oldest sibling) was much more predisposed to become a radical innovator than most other contemporary biologists.
The Marxist view of history emphasizes the importance of class in molding social attitudes, for instance in breeding lower-class radicals who revolt against entrenched upper-class conservatives. But that perspective leaves unexplained the often stunning differences in attitudes between members of the same class, and even of the same family. Differences within a family are especially perplexing because of two undoubted facts that tend to produce convergence within families. First, father and mother tend to share social attitudes and political views, because agreement on those matters turns out to be one of the strongest predictors of who marries whom—much stronger than any bodily attribute related to sex appeal. In statistical language, the correlation coefficient between political views of spouses averages +0.9, where +1.0 would mean perfect agreement, 0 no relationship, and -1.0 complete disagreement. Second, the corresponding correlation coefficient for the views of parents and offspring is +0.47: not as high as that between spouses, but still indicating substantial agreement. Nevertheless, +0.47 still leaves room for plenty of disagreement among siblings, and between children and their parents.
To resolve these puzzles, Mr. Sulloway analyzes his usual huge database for effects of his usual large number of variables on political and religious attitudes. Class proves to have very little effect, but birth order has a large effect. Mr. Sulloway’s complete panoply of variables (including birth order, class, and many others) has ten times the effect of birth order alone and 138 times the effect of class. All other things being equal, firstborns tend to be more conservative than laterborns, and older people more conservative than younger people—but many other things are often unequal.
As in other matters, firstborns conform more to their parents in social outlook, whether liberal or conservative, than do laterborns. Children whose birth order is the same as that of their parents conform more to their parents’ views than do children differing in birth order from their parents. For example, while landowning nobles tend to be conservative, that is not, Sulloway argues, because they belong to the upper class (there have been innumerable upper-class radicals) but because of the compounding psychological effect of many generations of primogeniture. Landowning nobles tend to be the oldest child of an oldest child (who often chose another oldest child as spouse) going back many generations. For the converse phenomenon of a father and son at opposite poles in birth order and political views, consider the case of Benjamin Franklin, the fifteenth of seventeen siblings and the youngest son of a youngest son for five generations. While Franklin helped draft the Declaration of Independence at the age of seventy, his oldest son remained a Loyalist throughout the American Revolution, moved to England after the Revolution, and became completely estranged from his father as a result of their political differences.
Because birth order, in its effect on political views, interacts with many other variables that collectively have a much larger effect than does birth order alone, one should not be surprised to find firstborns as well as laterborns among famous revolutionaries. However, Sulloway writes, there are differences between the styles of firstborn and laterborn revolutionaries. Consistent with other aspects of their personalities, firstborns, who as children may be in a position to behave as uncompromising terrorists toward their younger siblings, tend to carry that tendency over to their revolutionary strategies as politically active adults. The long list of revolutionary terrorists who had law-abiding younger siblings includes Robespierre, Carlos the Jackal, Mussolini, Che Guevara—and, allegedly, Theodore Kaczynski.
Mr. Sulloway illustrates these conclusions with large-scale analyses of participants in the Protestant Reformation and also in the French Revolution, once considered the classic Marxist example of class struggle. For instance, he tabulates the votes, birth order, and personality characteristics of all 893 deputies of the National Convention at the height of the French Revolution’s Terror. Mr. Sulloway’s readers won’t be surprised to learn that, at the crucial vote on whether to pardon or execute King Louis XVI, 73 percent of the firstborn deputies voted tough-mindedly for execution, while 62 percent of the laterborns voted for pardon as a compromise. Of course, that leaves 27 percent of firstborns and 38 percent of laterborns whose votes are not explained by birth order. But, here as elsewhere, Mr. Sulloway considers birth order merely as the most influential among many variables, of which he tests seven for their relation to the vote on execution vs. pardoning.
Such differences between the political views of firstborns and laterborns carry over into smaller databases as well. Among the items that Mr. Sulloway cites, 96 percent of Reformation Protestant martyrs in Catholic countries were laterborns, but only 33 percent of Catholic martyrs in Reformation Protestant countries. Recent Republican presidents have tended to appoint firstborns as Supreme Court justices, while Democratic presidents appoint laterborns. Firstborn justices, formed by a childhood of obeying their parents, issue significantly fewer dissenting opinions than do laterborn justices. Among King Henry VIII’s six marriages, the happiest was to firstborn Catherine Parr (she obeyed him), while the two ending in beheadings were to laterborns Anne Boleyn and Catherine Howard (they made the mistake of defying him).
I said earlier that Mr. Sulloway’s book really consists of four books rolled into one. Three of those sub-books deal with family influences on personality, scientific creativity, and political revolutionary tendencies, as I have been discussing. The last sub-book treats a still broader theme: how to pursue studies of human behavior scientifically.
There is, of course, already a gigantic literature on each of Mr. Sulloway’s first three themes. Most of it, however, belongs to the humanities or to the discipline of history rather than to the sciences. I don’t say this to denigrate that literature, but simply as an observed fact about methodology. Indeed, there are obvious reasons why authors shy away from pursuing these themes by the methods of science. The creativity of even a single individual, even one person’s personality, the origins of even a single revolution, are overwhelmingly complex problems. Each is influenced by a myriad of variables, many of them apparently unique to that person or revolution. If we have such difficulty understanding a single example, what could be more daunting than to aspire to a comparative study of 893 examples? Instead, the traditional form for treatments of these three problems is the case study: a psychoanalytical case study of one person, a biography of one scientist, a history of one revolution. Only after we have understood many individual examples can we hope to generalize—or so it might seem.
But the case study method, as it is usually pursued, suffers from a crippling drawback. It does not apply “scientific methods”—a phrase that makes non-scientists uneasy, but that really means nothing more than is implied by its Latin root, scientia (knowledge): methods useful for extracting knowledge, and for curbing one’s tendencies to stamp one’s pre-existing interpretations on data as they accumulate. The scientific method involves viewing each particular problem within a broad context of related problems, posing and testing competing hypotheses, defining dependent and independent variables, measuring them, making predictions about their relations, and testing those predictions, preferably with statistical measures of significance. The absence of this methodology means that biographies, histories, and psychoanalytical case studies run the risk of becoming Rohrschach tests in which the author interprets the data according to his or her pre-existing view. One has only to compare two biographies of the same person by different authors (e.g., those of Bismarck by A.J.P. Taylor and by Ludwig Reiners), or accounts of the same historical event by different authors, to appreciate this dilemma.
Those who are tempted to write off scientific methodology as inapplicable to complex problems of human behavior might reflect on its routine application to other complex problems universally subsumed under fields of science. For example, how many species of plants or animals does one expect to find on an island? It depends on a host of variables and their interactions, such as the area, elevation, geological history, habitat diversity, isolation, and productivity of the island, and the body size, fecundity, life span, overwater dispersal ability, and population density of the plants and animals involved. Yet island bio-geographers manage to define and measure these variables, to use them to test competing hypotheses, and thereby to predict with considerable accuracy an island’s number of species, as well as to measure the effect of each factor far more convincingly than if one attempted to detect its effect by itself.
While Mr. Sulloway does not explicitly draw an analogy to the science of island biogeography, he does explicitly defend the same rationale in his studies of human personality. When one analyzes anything as complex as islands or humans, one cannot reasonably expect a single explanatory factor to explain much. Instead, one must be prepared to deal with large numbers of variables and their interactions. Faced with this dilemma, most biographers and historians don’t even try to apply scientific methods. To me, Mr. Sulloway’s most basic contribution is to show that they can indeed be applied profitably, even to biographies and histories. For instance, his family-dynamics model of radical scientific thinking employs eight variables about the scientist, seven interaction effects between those variables, and another variable about the scientific revolution itself. It thereby succeeds in correctly classifying two thirds of all scientists, and 89 percent of scientists from extreme family backgrounds, concerning their attitudes towards a scientific revolution.
Even if one’s interest is in understanding a single scientist, patient, or political revolution, this method has the advantage of setting the case within a broad context, and thereby permitting one to recognize what (if anything) is truly idiosyncratic about the case under study. For example, psychoanalysis has attracted numerous women noted for their challenges to Sigmund Freud’s views, including Helene Deutsch, Karen Horney, and Melanie Klein, all of them lastborn (among their four, two, and four siblings respectively). It seems at first paradoxical that the equally distinguished and able Anna Freud was much more conservative, even though she was the youngest of Freud’s six children and for that reason even more predisposed to rebel. But we now know that she was psychoanalyzed by her father—not a variable coded in Mr. Sulloway’s formulas, but nevertheless a potent, idiosyncratic way to reduce “resistance” to her father’s theories. Mr. Sulloway devotes an entire chapter of his book to such idiosyncratic “exceptions to the rules.”
Where will Mr. Sulloway’s book lead? The bane of an author who has just written a big book is a reviewer who wishes the author had instead written a somewhat different big book. Slipping into that expected role, I note that most of the twenty-eight scientific revolutions analyzed by Mr. Sulloway took place in the nineteenth century or earlier, and that only one of his twenty-eight analyses—of continental drift—extends beyond the year 1950. I wish that he had also analyzed recent scientific controversies. Since many of the people who took part in them are still alive, I would have thought that it would therefore be possible to determine attitudes and family variables much more accurately for them than for long-dead scientists. For instance, a current battle among biologists involves a theory of biological taxonomy, termed cladism, which was promulgated in the 1950s and which classifies plants and animals on the basis of their evolutionary relationships alone. Its early advocates behaved with revolutionary zeal and denounced classical taxonomists, until cladism became widely accepted and its advocates more sedate. Did early cladists tend to be laterborns, and did the classical taxonomists whom they denounced tend to be firstborns? Analysis of the membership list of the Willi Hennig Society (a society devoted to cladism and named after its founder), with the years of joining, should be instructive.
Another possible extension, to which Mr. Sulloway himself devotes a page of exploration in an appendix, would be to Nobel Prizes, which in the popular mind are virtually synonymous with scientific revolutions. Molecular biologists who turn to biographies of Nobel laureates James Watson, Francis Crick, and Linus Pauling, the contestants in the famous race to solve the structure of DNA, in order to learn their birth orders will be surprised to discover that all three were firstborns, seeming exceptions to Mr. Sulloway’s generalization about revolutionary tendencies of laterborns.
Here, as elsewhere, we can raise the question whether some of Mr. Sulloway’s many variables other than birth order will prove important. And we might consider as well that, in reality, many or most Nobel Prizes are not awarded for scientific revolutions but for the reverse: clever problem-solving within an established frame. Do ambitious little firstborn tyrants who bully their younger siblings, obey their parents, and study diligently at school thereby increase their likelihood of becoming represented among Nobel laureates? This would be a promising question for a researcher who wants to carry forward Mr. Sulloway’s fascinating and convincing work.
‘Born to Rebel’ April 24, 1997