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The Claim: Birth Order Influences Intelligence

Published: April 18, 2006

THE FACTS Are most older siblings smarter than their younger brothers and sisters? The scientific literature is rife with studies claiming that I.Q. scores and other measures of intelligence dwindle among siblings with decreasing age, a phenomenon scientists have attributed to strains on parents' time and resources as their families expand.

But in the past few years, a handful of studies have found that the so-called birth order effect might be more myth than reality.

A study this year by scientists at Ohio State University analyzed data on siblings from 3,000 families collected over 12 years. The researchers found that whether siblings were born first or last in their family generally had no effect on intelligence scores.

But children in large families, primarily those in which the mother had her first child at a young age, had lower scores than those in smaller ones. Children in large families generally had high scores only when their mothers were older.

The scientists, who published their findings in the journal Personality and Social Psychology, speculated that the reasons behind this were socioeconomic. Younger mothers were more likely to have lower incomes and less education — factors that could negatively affect their children's test scores, said Aaron L. Wichman, the lead author of the study.

"A mother's age is associated with many variables that can affect the child-rearing environment," Dr. Wichman said. "It's not your birth order that's important; it's your family environment and your genetics that really matter."

THE BOTTOM LINE Birth order does not appear to have any effect on intelligence.

Brain Power: The Search For Origins

Published: November 5, 2002

Neuroscientists have found an evocative solution to a classic problem: which is more important in shaping the human brain, nature or nurture?

Their answer is complex. The brain is not primarily the product of genes, they say, but neither is it simply the sum of one's experiences. Rather, they say, each human brain is constructed of complex neural circuits that start taking shape before birth and continue to grow and change throughout life as genes and cells are influenced by environment, experience and culture.

There is widespread agreement that genes and environment interact in brain development, said Dr. Terrence J. Sejnowski, a neuroscientist at the Salk Institute in San Diego, and a leading proponent of the new synthesis. The new idea, he said, is that human cultures, which teach children what to believe and what to expect in life, interact with cell biology and molecular genetics to assemble the highly social human brain.

Though everyone's brain begins with ''a basic scaffold of connectivity that is formed according to genetic blueprints,'' said Dr. Carla Shatz, a developmental neurobiologist at Harvard Medical School, ''a baby's brain is not a miniature of the adult's, but rather is a dynamically changing structure.'' Experience alters brain structure, chemistry and gene expression to sculpture immature neural circuits into adult circuitry, she said.

In short, the theory's advocates say, while the brain directs people's activities in everyday life, the activities themselves shape the brain throughout life.

''The attempt to separate genes and environment is a mistake,'' said Dr. Steven R. Quartz, a scientist at the California Institute of Technology. ''What makes us who we are is a complex interplay of early experiences, parenting, birth order, friends, genes and how these forces interact.'' He and Dr. Sejnowski wrote ''Liars, Lovers and Heroes,'' published last month, which outlines details of what they call cultural biology.

Another book making similar arguments, ''The Origin of Minds,'' is to be published this month. Its authors are Dr. Peggy La Cerra, a neuroscientist and president of a consulting firm in Ojai, Calif., and Roger Bingham of the Center for Brain and Cognition at the University of California at San Diego.

Scientists and philosophers have argued about the role of culture in shaping the brain for millenniums. Plato and Artistotle argued over whether human traits like virtue were inborn or learned. Darwin's ideas led many scholars to declare that human traits were inborn, with each racial group at a different level of evolution, a view that culminated in the unbridled eugenics of the Holocaust.

The backlash was an era of cultural relativism, which saw the newborn brain as a blank slate that evolution had no part in.

A new battle over human nature began in the 1970's, when Dr. Edward O. Wilson argued that human behavior, like that of other animals, was a product of the evolutionary pressures of natural selection. Evolutionary psychologists adopted this argument, using it to explain everything from sexual differences in dating behavior to the appeal of potato chips.

The advocates of the new neurobiological view say it is time to look more closely at the evidence for evolutionary psychology's position.

''It's true you can't separate the question of who we are from the world our ancestors passed through on their way to becoming us,'' Dr. Sejnowski said. But that evolution did not occur in the relatively stable savanna described by evolutionary psychologists, he said, but rather during a period of unusual, extreme and rapid oscillations in climate. If the brain evolved any trait during the Pleistocene, he declared, it was flexibility.

While it is true that different brain regions tend to specialize in different functions, like language or face recognition, Dr. Sejnowski said, these areas are very changeable and not hard-wired modules.

Humans are born with temperaments arising from genetic variations in brain chemicals called neuromodulators, Dr. Quartz said. These differences may lead one baby to avoid novelty and another to seek it. But the experiences that result help construct the growing brain.

Humans are also born with a very large prefrontal cortex, a higher brain region involved in planning that taps into an ancient system for predicting what is rewarding and making decisions to maximize rewards and avoid punishments.

Neuroscientists are finding that this circuit, which fully matures in late adolescence, is an internal guidance system that fills each person's world with values, meaning and emotional tone, taking shape according to a person's culture.

In other words, culture contributes not just to the brain's contents but to its wiring as well, Dr. Quartz said.

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Historian Links Birth Order To Innovation

By DANIEL GOLEMAN (NYT) 1925 words
Published: May 8, 1990

COPERNICUS, who shattered traditional cosmology by contending that the Earth revolves around the Sun, was the second of four children. His bitter opponent, Tycho Brahe, was an only child. 

Charles Darwin, whose theory of natural selection overturned traditional views of the creation and evolution of life, was the fifth child of six and Alfred Russell Wallace, the co-discoverer of the theory, was the last of six children. But George Cuvier, an upholder of the creationist view, was the first child of four, as was Louis Agassiz, another opponent of Darwin.

Frank Sulloway, a historian of science who proposes that birth order makes a startling difference in the progress of science, is himself the third of four children.

Dr. Sulloway cites the roles played by these and thousands of other scientists as prime evidence for a provocative theory: researchers who challenge established views tend to be born later in their families while those who support the status quo tend to be firstborns.

His proposal comes at a time when the idea that birth order makes any difference in behavior is under fierce attack by social scientists. Despite the attacks, the birth order concept is an idea that will not die. Dr. Sulloway's study is perhaps the most elaborate among the continuing efforts of dozens of researchers to find a link between birth order and such things as managerial ability, drug abuse, criminality, and teen-age pregnancies. In 1988 and 1989 there were 45 scientific reports on birth order, more than a third of which found it had no effect.

Dr. Sulloway, who is now a visiting scholar at the Massachusetts Institute of Technology, may be living proof of his own theory. His first major work, ''Freud: The Mind of a Biologist,'' in 1979 scandalized orthodox psychoanalysts by saying that Freud borrowed much of his theory from the biological thinking of the period.

Now Dr. Sulloway has done it again. After years of research, he has proposed that firstborns are more likely to defend current theories and those born later are more likely to attack them. In the process, he is resurrecting the notion that birth order can to some degree steer personality in later life, an idea that most social scientists have come to reject.

''I'm skeptical of any reported effect for birth order,'' said Judith Blake, a sociologist at the University of California at Los Angeles. '' People get excited by the idea of birth order, but when you look at it scientifically, it evaporates.''

Support From Some Psychologists

But Dr. Sulloway's studies are finding support among some eminent psychologists.

''He has solid data,'' said Robert Zajonc, a psychologist at the University of Michigan. ''I can't argue with what he's found.'' Jerome Kagan, a psychologist at Harvard, called Dr. Sulloway's work ''the most extraordinary birth-order effect I've ever seen.''

Dr. Sulloway, a recipient of a MacArthur Foundation award, came to his view through the diligence of 19 years' labor and the assistance of scores of colleagues. For the last five of those years he squirreled himself away in a small, windowless office at Harvard.

There Dr. Sulloway finished his analysis of 2,784 participants in 28 major scientific controversies in the last 400 years. He included the 20 or so great revolutions of science, as well as some obscure controversies like the debate over phrenology. The main criterion was whether enough remained in the historical record about the scientific debate to evaluate the main participants.

Though he largely worked alone, he turned to nearly a hundred colleagues in the history of science, asking them to nominate the scientists to be studied. The historians judged the stands each scientist took, as well as as the scientist's political and religious views, family size and 40 other variables.

Birth Order and Innovation

Birth order was by far the strongest predictor of whether a scientist would accept or reject radically innovative ideas.

Of the 28 scientific revolutions, 23 were led by later borns. And in those with a firstborn as the leader - Einstein and Newton, for example - their prominent allies were for the most part later borns.

Of the 2,784 participants studied, 37 were siblings who joined in the same scientific controversy. Of the 7 firstborns among them, 6 opposed the radical new ideas being debated. And of the 30 younger siblings of these firstborns, 27 were supporters of the innovation.

''The overall probability that a firstborn will suppport a scientific revolution is 34 percent; the odds that a later born will do so are almost double: 64 percent,'' Dr. Sulloway said.

Dr. Sulloway reported the findings at the meeting of the American Association for the Advancement of Science in February. Since he announced his findings, they have sparked continuing controversy even though they are yet to be published.

Reformers Likely to Be Born Later

In studies currently underway, Dr. Sulloway is finding the same birth order effect at work among social reformers in historical movements like the abolition of slavery, civil rights, union organizing and women's rights.

''Later borns have a greater tendency to be reformers of all kinds,'' he said. ''For instance, the Protestant Reformation largely split noble families by birth order.''

Dr. Sulloway explains the conservatism of firstborns by their relationship with their parents. ''As the eldest, firstborns identify more closely with parents, and through them, with other authorities,'' he said. ''And they play the role of parental surrogate to later children. They end up more conforming, conscientious, and conventional than later siblings.''

On the other hand, he said, later siblings tend to rebel against the firstborn's authority.

''For the firstborn, it's taking over for daddy, being a responsible member of the establishment,'' said Dr. Zajonc. ''The younger ones grow up testing the limits, seeing what they can get away with.''

Despite a handful of influential defenders like Dr. Zajonc, Dr. Sulloway's theory is encountering a scientific attitude that is skeptical of any birth order studies.

Family Size Seen as More Important

Last July, Dr. Blake published data in Science showing that for 113,000 people, the order of birth made no difference in how far they went in school or how intelligent they were, despite earlier studies suggesting that firstborns had an advantage.

''What matters instead,'' Dr. Blake said, ''is how large a family one comes from. What had seemed to be birth order effects were artifacts. The real effect was due to parents' characteristics - the lower the social class and the less educated the parents, the bigger the family.''

Whatever small differences had been found, Dr. Blake said, were due to the statistical weight of those born seventh or later in families of poorer, less educated parents. Thus what seems to be an effect of birth order actually reflects the family's economic and educational status, Dr. Blake said.

Dr. Blake's attack on birth order theory came on the heels of a 1983 book ''Birth Order,'' written by two Swiss psychologists, Cecile Ernst and Jules Angst. A massive review of scientific studies, their work came to much the same conclusions as Dr. Blake: on closer scrutiny, virtually all the hundreds of findings about birth order are due to other factors like family size and economic status.

That includes the well-known findings, first proposed by Sir Francis Galton in 1874, that firstborns tend to rise to positions of eminence more than later borns.

But Mr. Sulloway used statistical methods that corrected for the influence of family size. He also pointed out that in their devastating critique of the birth order literature, Dr. Ernst and Dr. Angst found that one of the few ideas supported by well-done studies is that firstborns are more accepting of parental authority and identify more with their values than do those born later.

But, they noted, that has been shown only in studies with children and adolescents. Dr. Sulloway's is among the first to show it with adults.

Birth Order and Personality

Dr. Blake could not comment directly on Dr. Sulloway's study. ''I haven't seen his data,'' she said. But, she added that in a project now underway, she is analyzing data from almost 10,000 people to see if there is any relationship between any personality trait and birth order.

''I don't get anything for either birth order or family size on any personality variable, including conformity, sociability, anxiety and assertiveness,'' Dr. Blake said.

But some other recent findings fit well with Dr. Sulloway's theory. For instance, a study of 835 accountants published in 1988 found that firstborns scored higher than those born later on tests of dominance and leadership ability, of wanting to make a good impression and of achievement through conformity rather than through independence.

''The firstborns are more conformist because of their parents' expectations,'' said Arthur Bedeian, a professor of management at Louisiana State University and one of those who conducted the study. ''They're put in a leadership position from their early years, standing in for their parents in caring for the younger ones. The younger children, though, are freer to be independent, to define themselves by other standards.''

Some recent studies, like Dr. Sulloway's, are generally designed to overcome the objections of Dr. Blake and other critics. From some of the studies have come entirely new twists to the birth order concept.

For example, data from 7,018 children rated from birth to age seven showed that there was a direct relationship between birth position and the child's activity level. Firstborns were the most active, second children more active than third and so on.

''The finding surprised us,'' said Dr. Judith Chipperfield, a psychologist at the University of Manitoba and one of those who did the study. ''Children who are more active early in life learn more from their environment; they're more stimulated.''

Another new perspective holds that it is not birth order at play as much as the age of the child's mother. That position is taken by Stanley Coren, a neuropsychologist at St. Lawrence University in British Columbia. Noting that later born children have a greater chance than firstborns of being left-handed, Dr. Coren has proposed that is due to the mother's aging.

Children born to mothers in their early 30's are a third again more likely to be left-handed than children born to mothers between 17 and 24 years of age, while children born to mothers older than 40 are more than twice as likely to be left-handed.

The finding is of significance, Dr. Coren said, because about half of left-handed children have neurological indicators of problems in brain development, like dyslexia and other difficulties in problem-solving. Left-handed children also have more auto-immune diseases like allergies.

For her part, Dr. Blake remains skeptical of all the birth-order findings. ''I can't think of a domain where there's a genuine birth-order effect. Every time you look hard at it, it turns out to be an artifact, usually of family size.''

Other researchers feel that birth order still has effects, though not nearly so widespread as had once been thought. ''The psychology of birth order has a tiny effect, if any, on things like intelligence,'' said Dr. Zajonc. ''But it may be far more important in areas of life such as upholding traditional values and conventions or questioning them.''




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