The Sibling Effect

In 1883, the year Elliott began battling what was then known as melancholy, Teddy had already published his first book and had been elected to the New York State assembly. By 1891—about the time Elliott, still unable to establish a career, had to be institutionalized to deal with his addictions—Teddy was U.S. Civil Service commissioner and the author of eight books. Three years later, Elliott, thirty-four, died of alcoholism. Seven years after that, Teddy, forty-two, became president.

Elliott Roosevelt was not the only younger sibling of an eventual president to cause his family heartaches—or at least headaches. There was Donald Nixon and the loans he wangled from billionaire Howard Hughes. There was Billy Carter, hawking beer and talking loose and trying to intervene with the U.S. government on behalf of the pariah state Libya. There was Roger Clinton and his year in jail on a cocaine conviction. In the book A Treasury of Great American Scandals, author Michael Farquhar cites similar cases even earlier in history: Randolph Jefferson, the younger brother of Thomas, was widely seen as both reckless and clownish, forever at the edge of bankruptcy as a result of one ill-considered business deal or another. One of the president’s slaves captured the general perception best when he said, “[Randolph] was one mighty simple man.” Orvil Grant, little brother of Ulysses, conspired with Secretary of War William Belknap to solicit kickbacks from the sale of trading posts in the West, and was eventually called out for it by General George Custer during a Senate investigation.

In fairness to all of the little sibs whose big brothers land in the Oval Office, it can’t be easy being a runt in a litter that includes a president. But it couldn’t have been easy being Billy Ripken, either, an unexceptional major league infielder craning his neck for notice while the press swarmed around Hall of Famer and elder brother Cal. It couldn’t have been easy being Dom DiMaggio, with his .298 career batting average for the Boston Red Sox and his seven selections to the All-Star team, glittering achievements by any measure, until they’re compared to those of big brother—and New York Yankee—Joe.

Of all the things that shape who we are, few seem more random than the simple timing of our birth and how it compares with the timing of our siblings’. Maybe it’s your genes that make you a gifted athlete, an accident of brain chemistry that makes you a drunk instead of a president. But in family after family, case study after case study, the roll of the birth-date dice seems to have an odd and arbitrary power all its own.

For families themselves, this comes as no surprise. There are few extended clans that can’t point to the firstborn child with the heirapparent bearing who makes the best grades, keeps the other kids in line, and, when Mom and Dad grow old, winds up as caretaker and executor, too. There are few that can’t point to the lost-in-the-thickets middle-born or the wild-child last-born. And hard data support those everyday observations. Firstborns are disproportionately represented in Ivy League colleges, with one study revealing that 66 percent of incoming students were the oldest in the brood. This has knock-on effects later in life, with the exceptionally well educated similarly dominating whiteshoe law firms and investment banks. The firstborn edge applies even extraterrestrially: Twenty-one of the first twenty-three U.S. astronauts were firstborns or only children. By contrast, last-borns are looser cannons, less educated, and statistically more likely to live the life of an artist or a comedian, an adventurer or entrepreneur, a GI or a firefighter. And middle children? Well, they can be a puzzle—to families, scientists, and themselves, for that matter.

Even when people aren’t actually siblings, we sometimes can’t help but see them that way. There was always an odd brotherly quality to Bill Clinton and Al Gore’s partnership, with Clinton the flashy, popular, slick-talking big sib, forever eclipsing Gore, his studious little brother—unless of course you saw Gore as the disciplined and industrious firstborn and Clinton as the troublemaking baby. Ringo may have been the oldest Beatle, but he came across as every bit the goofy youngest. Paul and John seemed to battle for the firstborn crown, while George filled the role of the quiet middle-born. Buzz Aldrin, the second man on the moon, is seven months older than Neil Armstrong, the first. But if the men were brothers, would there be any doubt that the serious, sober Armstrong was the big sib, and Aldrin—with his product endorsements, bit parts on TV shows, and goofy turn on the prime-time hit Dancing with the Stars—was the little one?

Across the landscape of the behavioral sciences, real insights into human interactions usually require rigorous studies and decades of double-blind research. The power of birth order, by contrast, is something we always seemed to feel before scientists ever got into the game. “There are stereotypes out there about birth order, and often those stereotypes are spot-on,” says Delroy Paulhus, a professor of psychology at the University of British Columbia in Vancouver. “I think this is one of those cases in which people just figured things out on their own.”

But science is catching up, and what it’s revealing about the power of birth order is surprising even believers. According to a widely reported 2007 study by Norwegian researchers, firstborns are generally smarter than any siblings who come along later, enjoying on average a 3-point IQ advantage over the next eldest. The second child, in turn, is a point ahead of the third. Three points may not seem to amount to much, but consider that just 2.3 IQ points can correlate to a 15-point difference in SAT scores, which makes an even bigger difference when you’re applying to, say, Stanford or Yale with a 690 verbal score and are going head-to-head against someone with a 705. Once you have that academic leg up, there’s no telling where it can lead.

“Take a person who just manages to squeak into Harvard and the other one gets into some lesser college,” says the University of California’s Frank Sulloway, the widely accepted wise man of birth-order research. “The one who gets into Harvard meets a charismatic teacher and gets a summer job in the lab and gets taken on as a grad student and goes on to have an amazing career in science and wins a Nobel Prize. All of that can be a cascading effect that comes from a relatively modest difference.”

Behavioral scientists call such phenomena “threshold effects”—the seemingly inconsequential variable that leads to big results—and while Sulloway is surely overstating the case here, birth-order science is filled with similar examples. Studies in the Philippines show that later-born siblings tend to be shorter and weigh less than earlier-borns. Think the slight height advantage Peyton Manning, the six-foot five-inch quarterback of the Indianapolis Colts, has over Eli, his six-four little brother, who plays the same position for the New York Giants, doesn’t help when they’re trying to throw over the outstretched arms of a leaping lineman? The brothers’ lifetime stats certainly say it does.

More than the sibs’ careers are affected by birth order; their very health may be, too. Surveys show that younger siblings are less likely to be vaccinated than older ones. Kids with at least two older siblings are 50 percent likelier than other children to have been taken to an emergency room with asthma-related breathing problems, according to a study from Columbia University’s Mailman School of Public Health—probably due to increased exposure to infectious agents brought into the home by the bigger sibs. Second and third children also have a higher risk of diabetes than their firstborn sibs, with a 43 percent increase in cases for every five years of maternal age at birth.

As for the health-and-longevity disadvantages of being the eldest child? Not many, with the very significant exception that firstborns seem to run a greater risk of coronary heart disease. In a study conducted at a major cardiovascular rehab unit in Milan, Italy, firstborns represented 46.7 percent of all patients, yet they made up only 29.3 percent of the surrounding population. But even this undeniable downside may be a result of the eldest kids’ generally privileged lot. “The family context frequently orients them along a perfectionist path,” said Dr. Maurizio Ferrantini, head of the rehab unit. “[This gives] them a determined, competitive, winning and aggressive attitude—aspects frequently seen in subjects with a type A personality.”

It’s pointless, of course, for a later-born to be too resentful of a firstborn’s advantages, since many of them are unavoidable. You can hardly blame the eldest themselves for the fact that they’re born into a home with fewer child-borne pathogens than the younger ones experience. And if it’s maternal age that’s behind additional child health concerns, such as the increased risk for diabetes in younger kids, well, you can’t fight the simple arithmetic that makes Mom a little older every time she has a kid. Even the IQ advantage may be inevitable: Eldest kids get at least a year alone with their parents, which leads to a no-distractions period of intellectual stimulation. Firstborns are also needed to mentor and tutor their little brothers and sisters—whether it’s help with homework or merely shoe-tying—activities that are thought to have brainboosting powers of their own.

But these natural advantages are reinforced by culturally invented ones, too. It’s the oldest princes, after all, who inherit the castle, the land, and the crown. Younger princes get smaller sinecures and token responsibilities and spend their adult years, often as not, living the life of the dilettante. This can lead to trouble—and down through history it has. Britain’s Prince William, first in the line of succession to the throne after his father, Charles, gets his turn, has had a largely scandal-free young adulthood, while his little brother, Harry, has been snagged in serial embarrassments—boozing, pot smoking, wearing a Nazi armband at a costume party, and describing a fellow soldier who happened to be Pakistani as “our little Paki friend.” The British press tut-tuts at the incidents, but rarely evinces any surprise. Little royals have always been a handful, after all.

Among the nonroyal masses, firstborns are likelier to inherit the family business, control the family’s wealth, and be fawned over not just by mothers and fathers but by grandparents, aunts, and uncles, too—for whom that child is often the first baby of the new generation. While most parents will resolutely deny that they have a favorite child, the family scrapbooks, home movies, and other mementos tell a very different story. Says Laurie Kramer: “When a second child is born into a family in which there already is another child, we know they take fewer pictures and their photo albums aren’t as complete.”

My home reflected that perfectly. In the days of the eight-millimeter movie camera and home-editing machine, my father was a ferocious amateur moviemaker, shooting thousands of feet of films of Steve and painstakingly cutting, pasting, and editing them into finished products. He did the same with me, though the final library was decidedly smaller; with Garry it was smaller still. By the time Bruce came around, there was little footage shot at all, except for a few short rolls of unedited film that remained forever stored in the little yellow boxes in which they came back from the developer. (Our mother, with a more even hand and a greater appreciation for the signal such disparate archiving could send, was the one who handled our baby books, keeping them up to date until we reached seven—the prescribed age then for how long such record keeping should go on—and practically counting pages to make sure no one boy’s book was longer than any other’s.)

Still, familiar as all this sounds to anyone who grew up in a multi-child home or is raising kids in one, not all scientists are sold on the idea that birth order is as all-fired powerful as it seems. Stack up enough anecdotal maybes, and they start to look like scientific definitelys, but perhaps they’re not. There are doubts about the methods used to study the birth-order phenomenon, the objectivity of the scientists who come into the field, even the reliability of the reports from the sibs themselves. For many behavioral psychologists, there’s simply a reluctance to heap so much significance on any one variable when so many other X factors—income, education, culture, divorce—shape our personalities.

“We like structure, we like clarity, and birth order is beautifully clear,” says psychologist Aaron Wichman of Ohio State University, a birth-order doubter, who nonetheless concedes its appeal. “We know astrology is ridiculous, but tons of people like it. Well, birth order is more plausible than astrology.” If the best thing you can say about any science is that it’s more reliable than reading horoscopes, then it can hardly be a discipline worth studying. But such skepticism does not prevent more and more researchers from being drawn to birth-order research, and as they are, their findings—and the debates over them—continue to grow.

The puzzle of birth order has intrigued scientists for a long time—though in the early going the work was bungled badly. One of the first investigators to try to prove the birth-order effect was Sir Francis Galton, the nineteenth-century British anthropologist, geographer, and statistician who was best known not for pursuing those noble sciences but for inventing one that was decidedly ignoble: eugenics. It was his belief that the human species was ultimately perfectible—or at least improvable—if only people with desirable traits would marry among themselves, producing offspring who would carry on their genetic gifts and crowd out less desirable individuals. From there it’s a short leap to more pernicious ideas about racial supremacy and nations of supermen, and while it’s hardly fair to blame Galton because evil men later made that leap, it’s not unfair to charge him with playing a significant role in getting such thinking started. In a review of a biography of Galton, science journalist Dick Teresi once described him as a “comical British bonehead,” which is about the kindest thing people say about him these days.

Still, Galton seemed to get one small thing right. In his seminal 1874 book, English Men of Science: Their Nature and Nurture, he sought to determine the innate traits that highly accomplished scientists (or at least highly accomplished male English scientists) share. The work runs thick with eugenic muck about “purity of breed” and the lower classes as a sort of societal “residuum,” and even about the hair color and body type of the scientists’ parents and what this may say about the accomplishments of their offspring.

And then, amid all this hooey, came a nugget of science: Among 99 scientists sampled in one part of his study, Galton found that 26 were firstborns, 22 were only children (effectively firstborns), 36 were the middlings, and 15 were the youngest. “The elder sons,” he wrote, “have, on the whole, decided advantages of nurture over younger ones.” Their parents, he went on, treat them more like companions than like children. The firstborns, in turn, were likely to get more attention and better nourishment, which is particularly important in families of modest wealth, and this makes them “more likely to become possessed of independent means.”

Hold your nose at Galton if you like—and indeed you should—but here he was onto something, and nearly a century and a half later, similar numbers continue to back him up. Catherine Salmon of the University of Redlands reports that a firstborn’s allowance at any given age is likely to be higher than that of younger siblings when they reach the same age. Similarly, parents with limited income are more likely to invest in a computer for the oldest and let the younger sibs get by with scrounged or borrowed machines. And when it comes to paying for college, parents without the resources to educate the whole brood will most commonly invest in the firstborn—even if a later-born shows a greater aptitude for learning. Indeed, when Salmon tries to recruit subjects for her sibling studies, she often has to go beyond the college campuses that usually serve as such a good source of volunteers, since even in the modern age, the schools tend to be overstocked with firstborns. “Parents try to direct their investment evenly,” she says, “but most of the time it’s not going to turn out that way.”

A poll of corporate heads conducted by Vistage, an international organization of CEOs, takes this further, showing what the later-life implications of such early-life privileges can be. According to the survey, 43 percent of the people who occupy the big chair in boardrooms are firstborns, 33 percent are middle-borns, and 23 percent are last-borns. Steve Ballmer, CEO of Microsoft, is the eldest in his family. So is Charles Schwab of the eponymous commercial investment house; so is Michael Bloomberg, CEO of the Bloomberg news service and, effectively, of New York City, too. And so are—or at least were—the CEOs of companies as diverse as Avon, Medtronic, TD Ameritrade, Koss, and 1-800-FLOWERS.

Sandra Black, an associate professor of economics at UCLA, has found that firstborns in general earn more than later-borns, with income dropping about 1 percent for every step down the birth-order ladder. Eldest siblings are disproportionately represented among surgeons and MBAs, according to Stanford University psychologist Robert Zajonc. And a recent study found a statistically significant overload of firstborns in what is—or at least once was—the country’s most august club: the U.S. Congress. “We know that birth order determines occupational prestige to a large extent,” says Zajonc. “There is some expectation that firstborns are somehow better qualified for certain occupations.”

That expectation begins the moment firstborns emerge from the womb—the pampered princeling in what was until that moment a childless home. No parents are quite as giddy as first-time parents, nor quite as inclined to see their child as uniquely perfect, gifted, and deserving of their emotional and material resources. Such a belief can quickly become self-reinforcing as the flood of parental attention produces a fitter, smarter, more confident firstborn, leading Mom and Dad to invest even more in that child. Kids who come along later are hardly left with table scraps and parental indifference, but they do find themselves in a home in which they have to compete with not just any older child but one who’s been bred and tended like a hothouse rose. It’s no wonder the little sibs often fail to measure up.

The ferocity with which the Kennedy brothers fought to achieve great things, sometimes at lethal bodily risk—diving into crowds unprotected, speaking before audiences that on occasion were not just hostile but downright menacing—was often attributed to a decades-long quest to meet an impossible standard that Joe Sr., their larger-than-life father, had set for them. But the more compelling standard still might have been set by Joe Jr., the big brother who had been raised from the cradle to be president and then died during the Second World War, leaving an idealized legacy that could never be clouded by scandal or failure, and instead only grew shinier and less attainable with time.

As firstborns are growing up, they repay the parental favors they receive with loyalty. One of the reasons eldest kids tend to inherit the family business, for example, is that they’re usually the ones who have shown the most interest in it. “Firstborn siblings have an incentive to accept their parents’ worldview and excel along a dimension that is deemed important in their families,” says NYU’s Ben Dattner. “They defer to their parents and become comfortable with the idea of operating within an existing structure.” Firstborns also take on the so-called kin-keeper role—the sibling who assumes the task of organizing the reunions, gathering the extended clan for a funeral or birthday, even writing the family genealogy.

“The literature has always said that females are more inclined to be kin-keepers,” says Salmon. “But when I’d ask people to come do their family trees for me, I found there was a birth-order effect, too.” How pronounced that effect was usually depended on the particular subjects Salmon was studying, but again and again the kin-keeping behavior among firstborns did rise to a level that made it through the statistical noise and into the region of experimental significance. That’s the gold standard for any behavioral research, and in Salmon’s studies the data usually delivered. When the rule doesn’t apply—when the eldest shows little or no interest in kin-keeping behavior—there are often intervening variables that have scrambled the birth-order effect in other ways. A firstborn with health problems or emotional or behavioral issues, for example, will often cede the duties of the eldest to a second-born. Similarly, in families with a tradition of sending some of the children to boarding school, it is typically the firstborn who gets first crack. When that happens and the other kids stay home, those kids will become better family historians simply because they spend more time as an active part of the extended clan.

If eldest children recognize that they get more than their fair share of the family perks, it doesn’t escape the notice of the younger sibs that they get less than theirs. And while the firstborns are not inclined to rock the comfortable boat in which they find themselves, the later-borns are forever trying to capsize it. This isn’t so easy when being younger also means you’re smaller and weaker—a fact that firstborns exploit to their advantage, using what sibling researchers call a high-power strategy. “If you’re bigger than your siblings, you punch ’em,” Sulloway says.

But there are low-power strategies, too, and one of the most effective ones is humor. It’s awfully hard to resist the charms of someone who can make you laugh, and families abound with stories of last-borns who are the clowns of the brood, able to get their way simply by being funny or outrageous. Birth-order scholars observe that some of history’s great satirists—Voltaire, Jonathan Swift, Mark Twain—were among the youngest members of large families, a pattern that continues today. Faux bloviator Stephen Colbert—who yields to no one in his ability to get a laugh—often points out that he’s the last of eleven children. My youngest brother followed that pattern as well, and even spent the first decade of his career in theater, principally pursuing character roles in comedies and musicals. The younger of my two daughters similarly seemed to know very early how to use subtle tools, such as an arched brow or a change in inflection, to mine the most laughs from a moment. And while a theatrical temperament may be as much an accident of birth as anything else, the traits children develop fully and the ones they let languish are more a matter of choice and circumstance. In the case of most last-borns, humor is usually a trait that gets a lot of exercise.

Other forms of artistry also get a workout, and here the later-borns may wind up happier than the eldest. My father was the older of two boys, and was deeply invested in winning the approval of their father. This brought him repeated frustration—particularly when his plans to assume control of the family business were aborted just before his graduation from college. My father’s little brother, Richard, was spared much of this and had the breathing room to develop his own skills and choose his own career. He eventually chose journalism and later became a prolific author of both novels and historical nonfiction. Two of his books, Simple Justice, about the landmark 1954 school desegregation decision, and The Paper, a history of the Herald Tribune, were nominated for the National Book Award. A third, Ashes to Ashes, a history of the Philip Morris company, won a Pulitzer Prize in 1997. Would any of that have happened if he had been a firstborn? I have no idea. I do suspect that if he had the chance to replay his life and run that experiment, he’d wisely decline.

Part of being an artist is having a keen sense of human behavior, and here, too, do last-borns benefit. Personality tests show that firstborns tend to excel on the dimension of temperament known as conscientiousness—a sense of general responsibility and a tendency to follow through—while later-borns score higher on what’s known as agreeableness, or the simple ability to get along with people. “Being born later contributes to kids’ learning how to interact within a family, and that leads them to being more effective interpersonally in a lot of situations,” says Richard Zweigenhaft of Guilford College, who did the work that revealed the overrepresentation of firstborns in Congress. “Think about it: If you have to negotiate with an older sibling who’s bigger, stronger, maybe smarter—at least in that five-year-olds know more than three-year-olds—then you’d better find some ways to maneuver, and it may be through your interpersonal qualities.”

Even more impressive is how early younger siblings develop what’s known as the theory of mind. Very small children have a hard time distinguishing between the things they know and the things they assume other people know. A toddler who watches an adult hide a toy will expect that anyone who walks into the room afterward will also know where to find it, reckoning that all knowledge is universal knowledge. It usually takes a child until age three to begin learning that that’s not so—and effectively applying that insight to all situations takes longer still. Even now, Paloma, my seven-year-old, will occasionally begin a story about something that happened at school with a bit of phrasing like “You know that cabinet near the door where my teacher puts the pencils?” Um, no, I don’t—and I don’t have any way of knowing. Elisa, my nine-year-old, would be much likelier to begin the same story with the informational statement “There’s a cabinet near the door where our teacher puts the pencils.”

For children who have at least one older sibling, the theory-of-mind insight usually comes earlier and develops faster, and if the studies are correct, Paloma will fully outgrow her ingenuous assumption of universal knowledge at a slightly younger age than Elisa did, simply because she’s grown up with a big sister and has found it helpful to be able to intuit her thoughts. “When you’re less powerful, it’s advantageous to be able to anticipate what’s going on in someone else’s mind,” says Sulloway.

Later-borns, however, don’t try merely to please other people; they also try to provoke them. Zweigenhaft conducted a study in the late 1990s of a group of protesters who were staging labor demonstrations every Sunday at a Kmart near his campus. At some point, a faction of the group decided to engage in civil disobedience in order to press their grievances further, even if it meant being taken into custody. Zweigenhaft and a student from one of his classes interviewed the protesters and found that the later-borns were likelier than the firstborns to be part of that more militant subgroup. “It was a statistically significant pattern,” says Zweigenhaft. “A disproportionate number of them were choosing to be arrested.”

Such high-wire living extends to the boardroom as well. Dattner has found that when later-borns become CEOs, they approach their work very differently from the way firstborns do. Eldest sibs do best when they’re making incremental improvements in their companies: shedding underperforming products, maximizing profits from existing lines, and generally making sure the trains run on time. Later-born CEOs are more inclined to blow up the trains and lay new track. “Later-borns are better at transformational change,” says Dattner. “They pursue riskier, more innovative, more creative approaches.”

Dattner points to Andrea Jung, the firstborn CEO of Avon, who has been with the venerable company for sixteen years but has not reinvented it in any significant way—and never intended to. Instead, she has focused more on such unsexy details as operational efficiency—cutting waste and organizational redundancies—as well as advertising and marketing a proven line of products. Microsoft CEO Ballmer, also an oldest child, has won deserved plaudits for turning what was once a start-up company into a global juggernaut. But he has also been second-guessed for perceived stodginess, regularly upgrading an existing inventory of goods and services, but rarely coloring outside those lines in a way that allows the company to do anything truly transformative anymore. It’s this, critics say, that continually leaves Microsoft playing catch-up with more innovative competitors such as Apple and Google. Second-born George Soros, by contrast, earned his multibillion-dollar bankroll in part by taking very big risks with very big hedge funds.

“He bet $10 billion against the British pound in 1992,” Dattner says, “and he made $1 billion from that one transaction.” For all that, Soros describes his older brother, a successful industrial engineer, as “the real brains of the family.” That might be true, but it’s Soros himself who is the guts.

Later-borns are willing to risk not just their companies but their health and safety. All siblings are equally inclined to be involved in athletics, but studies have shown that younger ones are likelier to choose the kinds that can cause injury. “They don’t go out for tennis,” Sulloway says. “They go out for rugby, ice hockey.” Even when siblings play the same sport, they play it differently. Sulloway has collaborated on a study of 300 brothers who were major league ballplayers, and his preliminary findings revealed that older brothers gravitate toward positions that involve less physical danger—handling put-outs at first or chasing down fly balls. Younger sibs are the ones who put themselves more directly in harm’s way—crouching down in catcher’s gear to block an incoming runner, say.

George Brett, the fiery Hall of Fame third baseman who played for the Kansas City Royals, had more innate talent than his older brother Ken, a pitcher of middling gifts who played for the Red Sox, Pirates, Angels, White Sox, and Phillies. But George also had a more fiercely competitive temperament, which surely accounted at least partly for the success he enjoyed—and that big brother Ken didn’t. Paul and Lloyd Waner, infielders who played for multiple teams from the 1920s through the mid-1940s, are the only pair of brothers in baseball’s Hall of Fame, and show similar tendencies. Lloyd, the younger of the two, was somewhat taller, but he weighed only 132 pounds, which even then was small for a major-leaguer. He maximized what he had, though, making a career as a successful slap hitter who learned the game well, connected with the ball when he had to, and collected 2,459 career hits—well shy of big brother Paul’s 3,152, but still impressive. So tough an out did the Waner brothers prove to be that they became known by the nicknames “Big Poison” and “Little Poison.” The monikers suited them well even if, in some retellings, the roots of the name came from a Brooklynite mispronouncing the word “person”: “Them Waners!” the fan is said to have exclaimed. “It’s always the little poison on thoid and the big poison on foist.”

In a 2009 study published by the British Medical Journal, investigators at St. George’s Hospital Medical School in London found a similar birth-order effect among soccer players. Surveying fourteen clubs in one nationwide division, they found that the average number of siblings a goalkeeper had was 1.1; for defenders it was 1.8; for forwards it was 2.0.; for midfield players it was 2.4. The lower the number of siblings, of course, the likelier that a player will also be the firstborn. The investigators did not speculate about what was behind the relationship between birth position and field position, but goalkeepers may have things a little bit safer than players navigating the high-speed traffic in the middle of the field—again, consistent with the firstborn’s greater taste for risk avoidance. Salmon even sees a similar risk-related pattern at amusement parks. “The firstborns are usually afraid of the crazy rides,” she says. “The last-borns are willing to fling themselves in midair.” That’s another trait that was in evidence among my brothers and me, and is now turning up in my younger daughter, who loves roller coasters, and my older daughter, who loathes them.

As different as older and later-born siblings can be, in some ways the gap does close over time—but only between the firstborn and the very last born. The sibs at either end of their parents’ procreative arc, after all, usually have something in common: At some point, they’re the only child at home. They are thus the sole recipients of Mom’s and Dad’s attention, caregiving, and, sometimes, money, and that tends to bind them more closely to the family as a whole. Certainly, a firstborn experiences that parental attention very differently from the way a child who is, say, fifteen and the last one left when the bigger kids leave home. Indeed, the fifteen-year-old may actually want little to do with the parents—which is often the way things are with adolescents. But if the parent-child relationship is even a moderately good one, it’s likely to become better still in these later years. It’s probably for this reason that kin-keeper studies show that many last-borns are eventually as knowledgeable as firstborns when it comes to family genealogy, and may even be as conscientious when it comes to planning family events.

And what about middle sibs—the ones who never get this total-immersion parental love? Do they wind up less devoted to their families? Research says they do—in a thousand little ways. In one of Salmon’s studies, for example, she surveyed whom teenagers call for help when they get into car accidents and found that first- and last-borns typically call their parents, while middle-borns call a friend. In another, she recruited more than 100 college students who occupied different spots in their families’ birth-order hierarchies and played them recordings of political speeches. In some of the tapes, the speaker addressed the audience using kinship terms, such as “my brothers and sisters,” or spoke of the nation as a vast family. In others, terms of nonfamilial comradeship were used instead—“my friends” or “my fellow Americans.”

All such terms may have passed out of political vogue—“my brothers and sisters” sounds odd to contemporary ears, and “my friends” can sound strained and overly familiar–—but they have a long history in electoral politics and may still have the power to move us at an unconscious level. The key is which words suit which listeners. Salmon found that first- and last-borns were much more inclined to react positively to the politicians who chose kinship language, while middle-borns were drawn toward appeals to friendship. “Middle-borns don’t see their families as great sources of support, and so they don’t react to terms that invoke those relationships,” Salmon says.

If middle sibs seem ambivalently connected to their families, it’s partly because their very roles in those families are equally unclear. The youngest in the family, but only until someone else comes along, they are both teacher and student, babysitter and babysat, too young for the privileges of the firstborn but too old for the bemused tolerance given the last. Middle children are expected to step up to the plate when the eldest child goes off to school or in some other way drops out of the picture—and they generally serve when called, becoming what’s known as “functional firstborns.” The 2007 Norwegian intelligence study showed that when firstborns die, the IQ of second-born stand-ins actually rises a bit, a sign that they’re performing the hard mentoring work that goes along with the new job. Most middle sibs, however, are stuck for life in their center seat, and that may exact a psychological toll. Sulloway cites research showing that the U-shaped distribution of family resources—with the oldest and youngest at some point getting 100 percent of their parents’ time and care and kids in the middle always getting less—is paralleled by a U-shaped distribution of self-esteem, with the middle kids again exhibiting the lowest.

The phenomenon known as de-identification may also work against a middle-born. Siblings who hope to stand out in a family often do so by observing what the older child does and then doing the opposite. If the firstborn gets good grades and takes a job after school, the second-born may go the less disciplined, more ambling route. The third-born may then de-de-identify, opting for industriousness, even if in the more unconventional ways of the last-born. A Chinese study in the 1990s showed just this kind of zigzag pattern in homes (at least those that did not obey the country’s unpopular one-child policy), with the first child generally scoring high as a “good son or daughter,” the second scoring low, the third scoring high again, and so on. In a three-child family, the very act of trying to be unique may instead leave the middling lost, a pattern that may continue into adulthood.

This is not always the case, of course, and, depending on the talents and temperament of the child, being lost in the middle can actually be a good thing. The late Wendy Wasserstein, a Pulitzer Prize–winning playwright, was the middle child of three and, in a New York magazine story about power siblings, once said, “My talent was to accommodate larger personalities and observe; solid early training for a playwright.”

For Wasserstein, birth order was not destiny, and that can be the case for other middlings, too. Anthropologist Margaret Mead used to describe the kind of position a middle sib occupies as the pivot role in a family, and as demanding as it can be, it pays dividends. In the same way that middle managers in an office are often more interpersonally effective than the top dogs because they must learn both to defer to superiors and oversee subordinates, so, too, do middle sibs become more socially supple. This certainly seems anecdotally true. When parents describe the behavior of one of their kids with phrases like “Never been a bit of trouble” or “Always the easiest of the group,” it’s usually the middle child they’re talking about. Someone who knew my brothers and me well once described Garry, the archetypally easygoing middle child, as “the white sheep of the family.”

With such a complex body of evidence seeming to prove the power of birth order, it’s easy to conclude that the science is by now a slam dunk. Perhaps there’s more to explore in terms of the implications and specifics of the findings, but the broad ideas are no longer open to serious question. That, however, is nowhere near the truth; indeed, plenty of investigators believe that the real research hasn’t even begun, largely because the vast body of work that’s been conducted so far has been conducted all wrong.

One of the biggest problems, they argue, is that there is a whole constellation of other factors that shape emotional development, and some of them are so powerful that birth order might not get a chance to exert any leverage at all. The difference between growing up in poverty and growing up with privilege, for example, is surely a lot more defining than whether you happen to be a firstborn, a third-born, or even an only child. The same is true for education: An oldest child and a middle child who both finish high school and go on to college are going to have a lot more in common than a graduate and a dropout who both happen to be firstborns. Gender is a powerful wild card of its own—indeed, perhaps the most powerful, one that’s generally thought to account for at least twice the variance in a person’s temperament that birth order does. Culture, country of birth, the health of the family, and the presence or absence of a father in the home may all take precedence over birth order, too.

In an era of nontraditional families, your birth order may not even be a fixed thing. Zweigenhaft once asked the students in his psychology class where they fell in their family’s hierarchy, and got some surprisingly vague responses. “One girl couldn’t answer,” he says. “She said she was the firstborn child of her biological parents, but her parents adopted an older child, and she suddenly became the younger child. In the past, many people came from intact families, but now a lot of people are from single-parent families, blended families; they’re being raised by divorced parents, gay parents, remarried parents.”

Even in an unchanging family in which birth-order lines are firmly established, things can get jumbled. In a 2005 study, investigators at the University of Birmingham in Britain examined the case histories of 400 abused children and the 795 siblings of those unfortunate kids. In general, they found that when just one child in a family is abused, the scapegoat was usually the oldest, which would obviously break the close bonds the parents and the firstborns typically share. But the same rupture also occurs if a younger child is the one who’s taking the punishment, as the oldest turns from parental ally to protector of the brood. At the same time, the eldest may pick up some of the younger kids’ agreeableness skills—the better to deal with irrational parents—while the youngest learns some of the firstborn’s self-sufficiency. Abusiveness will “totally disrupt the birth-order effects we would expect,” says Sulloway.

The age gap between siblings is also a key variable. Sibs who are two years apart relate in very different ways from those who are four or five or eight years apart. Kip Gould, a publisher in New York City, and his wife, Joan Dineen, an architect, are the parents of kids who take that variable to an unusual extreme. Aiden, their oldest son, is twenty-three; Devin, the next eldest, is twenty-one; and Blythe, the youngest, is just eight.

“The boys were fifteen and thirteen when Blythe was born,” Gould says. “Devin seemed fascinated that here was this little thing to love, Aiden seemed less interested, but we didn’t say to either one, ‘It’s time for you boys to take care of your little sister.’ ” Now that both sons are out of college and Blythe is in fourth grade, their relationships are strong, but not in a traditional way. “It’s not the same as siblings who are closer in age,” says Gould. “It’s more like an uncle-and-niece relationship.”

Birth-order studies that fail to take into account the size of the family present problems of their own. The 1 percent reduction in income that each child down the age line earns as an adult tends to flatten out as the brood gets bigger, with a smaller earnings gap between a third and fourth child than between a second and third, and a smaller one still between the fourth and fifth, and on and on. The posited link between IQ and birth order may also be mitigated by family size. In small families with just two or three kids, parents do much of the tutoring and mentoring that are key to what the Norwegian researchers believe helps drive the intelligence of firstborns. In bigger broods, older kids pitch in more and are likelier to reap whatever IQ benefits there are to be had. “The good birth-order studies will control for family size,” says Bo Cleveland, associate professor of human development and family studies at Penn State University. “Sometimes that makes the birth-order effect go away; sometimes it doesn’t.”

Research by psychologist Aaron Wichman of Ohio State University casts further doubt on the IQ work, suggesting that maternal age is actually a bigger driver of a child’s intelligence than birth order, since the younger a mother is when she starts her family, the less education she’s likely to have had. That often means less intellectual stimulation for the kids during the critical period in which their analytic skills, vocabulary, and study habits are developing. Even the simple experimental precaution of administering two IQ tests to kids instead of one—the first when they’re seven or eight years old and the second when they’re thirteen or fourteen—sometimes makes the birth-order factor disappear, since this can correct for misleading findings that result from a smart child happening to have a bad day.

But the most grievous flaw in birth-order work, according to the critics, may be that the majority of the research is what’s known as between-family studies—comparing the firstborns in one family with those in dozens or hundreds or thousands of others, and then doing the same with second-borns, third-borns, and so on. That’s worse than comparing apples and oranges, the skeptics insist. It’s more like comparing apples and shoes. Between-family studies may minimize or simply ignore the manifold socioeconomic differences among families in favor of the single variable of birth order, producing results that are interesting but ultimately worthless. The alternative to between-family work is what investigators call in-family studies, a much more painstaking process requiring an exhaustive look at a single family, comparing every child with every other child, and then repeating the process again and again with thousands of other families. Eventually, you may find threads that link them all. It takes a lot longer to reach your conclusions, but they may be a good deal more reliable.

“I would throw out all the between-family studies,” says Cleveland. “The proof is in the in-family design.” And why don’t more birth-order researchers use that method? One reason, Cleveland believes, is a sort of unintentional bias. Birth-order researchers select into the field in the first place because they find the science compelling. They may be naturally disinclined to believe in an investigative method that could prove they’ve been wasting their time.

The debate over birth order will, of course, never be entirely settled. Family studies and the statistics they yield are cold and precise things, parsing human behavior down to decimal points and margins of error, which is how solid science is supposed to work. But families are a good deal sloppier than that, a mishmash of competing needs, moods, and clashing emotions, better understood by the people in the thick of them than by anyone standing outside. A firstborn alternately laboring with the burdens that come with the position and enjoying its fruits, a middle-born struggling for recognition, a last-born riffing and joking for laughs and love—all live very particular lives and have very particular emotions and histories. No psychologist is going to have much luck questioning those experiences. That won’t stop the scientists from looking for answers in their own way—and it won’t stop parents and siblings from looking in theirs.