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The Roots of Radicalism

Born to Rebel: Birth Order, Family Dynamics, and Creative Lives

by Frank J. Sulloway
Pantheon, 653 pp., $30.00


The case of the alleged Unabomber, Theodore Kaczynski, grips our imagination, not least as a psychological mystery of childhood development. Why might he have become a driven serial murderer? At first his curriculum vitae—child of liberal parents, Harvard College graduate, brilliant mathematician—might have seemed to point to another career. What was there in his genes or childhood environment that could have stamped him so powerfully?

Less attention has been paid to an even sharper paradox. Theodore’s brother shared approximately half of his genes and grew up in seemingly the identical family environment. Yet one Kaczynski boy may have devoted himself to killing, while the other turned in his brother for a capital offense. There could hardly be a greater contrast between possible lawbreaking and law-abiding behavior. It would be difficult enough to explain such opposites within the same city and social group; how do we explain them in the same family? This is among the questions suggested by Frank Sulloway’s study of siblings.

Polarization between siblings is something that any parent of more than one child witnesses dozens of times daily. For example, each day in the winter, when the heat is turned on in my house, my young sons engage in a battle that would be funny if they didn’t take it so seriously, and if I didn’t wonder about the possible effects of similar battles on the Kaczynski brothers. Before breakfast, both boys sit down to warm themselves on a floor heating grate with twenty-six slats. Each then counts whether his brother’s body unfairly covers more than thirteen slats, and loud arguments begin. The polarization extends to all spheres of life: Joshua beats Max at chess, so Max stops playing chess for two years; Max acquires a pet snake, so Joshua demands his own personal pet snake, then announces a passion for butterflies; and, of course, each complains that the other is receiving more of their parents’ attention.

Psychiatrists and psychologists have stressed the overwhelming formative influence of parents on children. In reality, many or most children spend far more time with siblings than with parents, whether at play, in laughing together, or in exchanging love, hate, and jealousy. Frank Sulloway’s big book explores the effects of those sibling relationships, but it really consists of four books combined into one. It begins by asking why a few scientists, such as Darwin, contribute revolutionary creative advances, while other scientists with superior brains and opportunities fail to do so. It then broadens its aim and explores the effects of family environment—especially of birth order, but also of other family variables—on the personality of anyone, not just of scientists. It turns to political and social revolutionaries and asks what molds them, from Robespierre to Fidel Castro. Through all these discussions runs the fourth theme: how to gain understanding in complex fields like psychology, biography, and history, where outcomes depend on many hard-to-quantify variables and on their interactions.

While a book about such difficult questions could easily degenerate into unreadability, Sulloway spices his pages with teasing problems and proposed solutions to them. What personal qualities enabled some of Henry VIII’s many wives to escape the fate of beheading that befell the others? Why did Che Guevara and perhaps Theodore Kaczynski become revolutionaries, while their brothers did not? What makes some Supreme Court justices especially prone to issuing dissenting opinions? The book’s last appendix is a worksheet enabling any reader to predict his/her own revolutionary tendencies at each of three different ages.

Siblings compete with each other. As children, we are exquisitely sensitive to perceived parental favoritism. That’s obvious even in modern, well-to-do, first-world families, whose children have to compete for nothing more than love and toys. How much more desperate was the struggle in the past, when many or most infants didn’t survive, and when the ability to compete with other siblings for limited parental resources (such as mother’s milk, food, dowries, and inheritances) spelled out the difference between life and death, or between comfort and poverty! Human beings evolved through natural selection to overcome not only rare risks, such as attacks by saber-toothed cats, but also the daily and more serious hazards posed by siblings. If you find it difficult to acknowledge that fact, look at what goes on in any litter of puppies or nest of hatchling birds as a model.

Each child must develop his or her own strategy for cornering parental resources, because what works for one child doesn’t necessarily work for another. Hence while children, already genetically different at birth but launched into the same family environment, are growing older, they become more rather than less different from each other. That divergence of ours is analogous to the divergent evolution, termed adaptive radiation, for which Darwin’s finches are famous, some species evolving heavier bills to crack seeds, others finer bills to glean insects. But whereas related animal species can only diverge slowly, over many generations, by accumulating genetic changes, human children have to do it within a few years, by developing different personalities and ways of behaving, for the most part unconsciously.

One of the most potent factors impelling siblings to pursue different strategies is birth order. Whether you’re older or younger than your sibling, hence temporarily stronger or weaker and more or less mature, has a big influence on what strategy could succeed for you. A newborn younger sibling is inevitably weaker and less smart than its older siblings for many years before it can catch up, if it ever does. Hence older children competing with younger siblings can often get their way by using their strength, bullying, asserting themselves, and dominating. Older siblings start out with another big advantage as well: parents have already made a big investment in them by the time that the next sibling is born. In all traditional human societies as in animal societies, the firstborn is usually the parents’ favorite, enjoying higher status. Who ever heard of a society where the youngest child customarily inherits the estate? It’s no accident that inheritance, for kings and landed gentry as for commoners, has so often been by primogeniture. Under the conditions of scarce resources prevailing for most of the world’s families, younger children serve as little more than a spare in case the oldest dies. That was the basis of the phrase used for Princess Diana’s expected contribution to England and to Prince Charles: to present them with “an heir and a spare.”

To overcome their disadvantage of a late start, younger children have to develop some strategy not based on brute strength. All of us who have been or have watched younger siblings know the alternatives, which include wheedling, developing social skills, appeasing or rebelling against older siblings, cultivating skills not already staked out by older siblings, and taking more risks. The latter tendency has a simple Darwinian explanation: if your chances of survival are lower, you have to take more risks.

These and other predicted differences between older and younger siblings are the subject of a large, somewhat inconclusive body of research by psychologists. Mr. Sulloway makes several useful contributions to sorting out the confusion. One is what is termed a meta-analysis: that is, using statistical methods to pool samples from different studies, and thereby to extract conclusions that each study individually fails to prove. For example, if you have a sample of only seventy teen-aged girls, that usually does not suffice to prove statistically even the uncontroversial acknowledged fact that eighteen-year-olds tend to be taller than fourteen-year-olds, but you can prove it with high probability if you pool 100 studies each of seventy teen-agers so as to have a sample of 7,000.

In this way, Mr. Sulloway tests, and for the most part confirms, a series of plausible hypotheses: that, compared to laterborn children, firstborns really do tend to be more concerned with achievement, more ambitious, angry, antagonistic, anxious, assertive, conventional, deferential to authority, dominating, identified with parents, jealous, and self-confident. At the same time they tend to be less empathetic, less willing to identify with the underdog, as well as less innovative and open to learning by experience, less rebellious, and less willing to take risks. As a result, firstborns are overrepresented among American presidents, British prime ministers, and participants in safe sports such as swimming and golf, while laterborns are overrepresented among sky divers and boxers.

If Mr. Sulloway were to stop there, any reader ought to howl in protest: But it isn’t so simple! What of all the exceptions that come to mind? Of course it isn’t so simple. Many other factors besides birth order affect personality. No more do all firstborns fit the stereotype of being jealous tyrants conscientiously following parental example than are all laterborns empathetic, rebellious race-car drivers. Personality can also be influenced by social class, age, and heritable features of temperament, as well as by many features of the family constellation other than birth order. Hence Mr. Sulloway proceeds to test the effects of many of these factors on personality, through a series of comparative studies. Among his conclusions are the following:

Marked conflict with a parent tends to make firstborns more open to experience, converting them into “honorary laterborns,” as exemplified by such firstborn innovators as Kepler, Newton, and Frederick the Great. Contrary to Freud’s Oedipal theory emphasizing the importance of conflict with the parent of the same sex, conflict with either parent proves to have similar effects on personality. Differences between firstborns and laterborns are greater in families with more siblings. Siblings differing by three to five years in age tend to become most divergent (for instance, the laterborns are most receptive to innovation, firstborns most resistant) and tend to converge when they differ in age by under three or over five years. The death of a parent while children are young tends to increase sibling divergence in lower-class families, because the firstborn child may have to function as a replacement parent, but to decrease it in upper-class families, where the availability of surrogate parents permits orphaned siblings to unite. That proves, Sulloway writes, to be one of the few well-established effects of class on personality.

The effects of the gender of a child and its siblings on the child’s personality are especially interesting. In the formation of so-called “masculine traits” (such as aggression, assertiveness, leadership, self-confidence) and “feminine traits” (being affectionate, cooperative, empathetic, flexible), a child’s birth order turns out to have nearly as large an effect as its gender. In a two-child family consisting of an older sister and younger brother, the sister’s personality is on the average more “masculine” than the brother’s, which is as “feminine” as that of the younger sister of an older brother. Birth-order effects noted for personalities of men also apply to women, as is illustrated by Phyllis Schlafly and Anita Bryant, firstborn women defenders of the status quo.

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