Are the family clichés true?

What kind of a person do you imagine when you think of an eldest child? Do you think of a conscientious, hard-working conformist? A proud brother or sister who shoulders responsibility – with or without encouragement? What if I were to ask you which member of your family is the most extroverted, or the naughtiest? Do you think of your younger sibling? Does the thought of a middle child conjure pictures of a tortured soul, forever torn between two extremes?

The difficult middle child, the spoilt only child, the wayward baby; few of us escape being labelled according to some sort of sibling stereotype. But what, really, are we to believe about the role our position in the family plays in determining our personality? Are the stereotypes true – or is the psychology of birth order just a load of hokum?

New research undertaken by scientists at the University of Oslo would suggest that there is, in fact, a good deal of truth in our family folklore. Using the IQ tests taken from the military records of 241,310 Norwegian conscripts, the scientists have found that eldest siblings are, on average, significantly "more intelligent" than second-borns. It may not seem like much, but 2.3 points on the IQ scale – the average difference between first and second siblings – could be enough to determine whether or not someone gets into a good college.

But what is equally intriguing about this study, which carries the kudos of having being published in the peer-review journal Science, is the way the scientists have tried to tease apart the possible reasons for this difference. Is it something that begins with gestation in the womb, or is it just the way siblings are reared within the family?

****

Biology certainly seems to play a role. Younger siblings tend to be shorter than older brothers or sisters, and the chances of being gay increase substantially according to the number of elder brothers a boy might have. But can biology and birth order within the womb explain these IQ differences, or is it down to upbringing within the family?

Petter Kristensen of Oslo University attempted to resolve this take on the "nature versus nurture" debate by looking at second-born siblings who, because of the early death of their elder brother or sister, had become the de facto eldest in the family at some point after their birth. What he found was pretty convincing evidence that it was not the fact of being born first that gave you an intellectual head-start in life; it was the actual role of being the eldest that was important. It was being reared as the eldest, rather than being born the eldest, that mattered.

"This study provides evidence that the relation between birth order and IQ scores is dependent on the social rank in the family and not birth order as such," Kristensen explains.

This latest argument has several enthusiastic supporters. Professor Frank Sulloway, who has become a leading proponent of the birth-order idea, has gone as far as to suggest that the Norwegian study dispels any previous doubts about the intellectual prowess of first-borns. Sulloway, of the University of California, Berkeley, says that any major criticisms of the birth-order idea – that the personality differences between families are so great that they obscure any differences within the families – can now be laid to rest. "At least in the domain of intellectual ability, the new Norwegian findings rule out this alternative explanation," he says.

In fact, he suggests that birth order helps to shape more than just intelligence. Since the publication in 1996 of his book on the subject, Born to Rebel, Sulloway says four different studies, involving more than 5,000 subjects from five countries, also support this contentious view. "They have shown that first-borns are rated as being more con

scientious, less agreeable, less extroverted – in the sense of being fun-loving and excitement-seeking – and less open to experience than later-borns," he says. "Several studies have shown that later-borns are judged to be the 'rebels' of the family and that they are actually more likely to rebel in real life."

Does this explain the studious, aspirational and conventional nature of famous first-borns such as Prince Charles, Tony Blair, Bill Clinton and JK Rowling? Are Ricky Gervais, Dawn French, Fidel Castro and Bill Gates helpful, affectionate, creative and sociable because they are middle children? Certainly, you could argue, the risk-taking, revolutionary characteristics ascribed to last-borns are the chief traits of Charles Darwin, Copernicus, Descartes, Mozart... and Ronald Reagan.

It's convincing stuff, is it not? The trouble with this sort of post hoc quasi-science is that it is a bit like astrology. Try to predict the birth order of those people mentioned above without first being told (admittedly difficult with the heir to the throne), and few people would get it right. After knowing their birth order, we find it quite easy to fit them into the appropriate personality pigeonhole – rather like reading a horoscope and finding that it neatly explains elements of your current situation.

Yet there is a long tradition of respectable science in this field. It began in 1874 with Sir Francis Galton, a cousin of Darwin and father of the eugenics movement, which did not then have the taint of disfigured ideology it picked up in the 1930s. Galton's book, English Men of Science: Their Nature and Nurture, was the first serious attempt to investigate whether birth order could explain a person's status or ability.

Galton chronicled the lives of some 180 distinguished scientists and collected birth-order data from 99 of his subjects. He revealed that 48 per cent of them were either first-born sons or only sons (the caveat being that Galton did not consider daughters at all in the equation; a first-born was judged to be a first-born even if he had several older sisters). It was convincing evidence, he argued, that being the eldest son in the family was seriously life-enhancing.

The first modern psychologist to study birth order seriously was Alfred Adler, an Austrian doctor who founded the school of individual psychology and formulated the theory of the inferiority complex. Working in the 1920s, Adler believed that first-borns are loved and nurtured by their parents who devote all their emotional and practical resources to the child until the arrival of the second. At this point, the first-born suffers feelings of what Adler termed "dethronement". No longer the centre of attention, the little prince or princess has to cope with feelings of parental rejection in favour of what was perceived to be a more popular younger sibling.

****

Adler went on to suggest that eldest children are most likely to suffer from neuroticism and feelings of excessive responsibility – and that the melancholy they feel from a very early age never really leaves them. Eldest children, Adler said, are more likely than later-borns to grow up to become alcoholics and substance abusers, and even criminals.

In families with three or more children, Adler believed that the youngest is more likely to be overindulged, pampered and spoiled – thus leaving it with poor social empathy. Middle children, he argued, who experience neither dethronement nor overindulgence, have the best chances of growing up into successful, well-adjusted adults. Interestingly, Adler himself was the second in a family of six. More interestingly still, he failed to provide any meaningful scientific evidence to back up these assertions.

Over the past 30 years, a huge number of studies have supported the view that birth order matters in terms of a person's lifetime success. And, contrary to Adler's conclusions about the psychological problems that come with being the eldest in the family, many have found that first-borns are more successful than later-borns.

****

Much of the research into birth order has concentrated on intelligence, and many studies have shown several overall trends. The first of these is that children of larger families tend on average to be poorer at IQ tests than children of smaller families, even when the studies take into account social class.

Second, first-borns tend to score better in IQ tests than second-borns, who tend to be better than third-borns, and so on up the birth-order scale. In other words, there is a gradation in intelligence that tends to flow down from the eldest to the youngest.

The third trend suggests that family size and birth order are linked to intelligence in such a way that, for example, the second-born of a three-child family is more likely to do better in IQ tests than the second-born of a five-child family.

In an attempt to explain why older children seem to have higher IQs than subsequent siblings, psychologists talk about the "resource dilution model" – the finite amount of money, personal attention and cultural stimuli, such as books, that parents can draw on to raise their children. First-borns have the initial advantage of having some of their early life without having to compete with later-borns.

Another important factor in being the first-born is that the eldest sibling is more likely to undertake the unpaid role of private tutor to his or her younger siblings. Many psychologists believe that this opportunity to tutor younger children improves the oldest child's verbal and cognitive skills. They learn by teaching, and this pays them dividends in later life – making them into leaders rather than followers.

Frank Sulloway suggests that sibling tutoring is the key to explaining why older children eventually maintain their overall supremacy in terms of IQ. "Through the organisation and expression of thoughts, teaching younger siblings is posited to benefit the tutor more than the learner, especially since last-borns have no one to tutor," Sulloway says. This may well explain the differences in IQ between first-borns and later-borns in the Norwegian teenage military recruits – and indeed other aspects of first-born intellectual prowess.

Or it may not. The canon of research in this field of psychology is contentious, to say the least. In 1983, two Swiss psychologists, Cecile Ernst and Jules Angst, carried out an exhaustive review of some 1,000 studies that had focused on the psychology of birth order, published between 1946 and 1980. In summary, Ernst and Angst delivered a devastating blow to the entire field by suggesting that the data on birth order was so flimsy and contradictory that many of the conclusions were not worth a candle. They even suggested that the lack of theoretical and practical rigour to the subject meant that a moratorium on birth order research was necessary until this fundamental problem had been ironed out.

More recently, other critics have lashed out at those they perceive to be peddling bad science. One of the most outspoken critics is Judith Rich Harris, an American psychologist and author of The Nurture Assumption, a treatise that tears apart the gamut of birth-order research. The belief that birth order accounts for personality traits, Harris says, can only be explained by "subjective impressions based on personal experiences, flawed or misleading research, the tendency for research to be published and publicised only if it supports the belief in birth order, the impressions psychotherapists get from listening to their patients, and biological factors".

****

Harris is perplexed that so many people continue to believe that birth order plays a significant role in forming adult personality. In a vitriolic exchange with Sulloway on the edge.org website, Harris explains that the strategies children learn to use at home to get along with siblings are not the same as those they employ outside home and in later life.

"This is why children's behaviour differs systematically in different social contexts. And that is why psychologists looking for birth-order effects in modern populations have again and again failed to find them," Harris says.

"It was different in the old days. In former times, children spent most of the day in the company of their siblings, so a younger sibling might spend his entire childhood in the shadow of an older brother. And the rule of primogeniture meant that a child's birth order determined his status not only within his family but in the society as a whole," she says. "Yet people go on believing in the power of birth order." Harris then goes on to criticise the statistical techniques used by Sulloway to justify his conclusions and much of the methodology employed in the studies he cites, which has often relied on parents being asked to assess their own family members.

She also cites the important issue of only children. Sulloway suggests that these children should in many ways be intermediate in terms of personality between the eldest and the youngest. They are not being pushed by a younger sibling into being particularly conscientious or aggressive, and they are not being pushed by an elder sibling into being particularly daring or unconventional. Sulloway's thesis – that there are ecological "niches" in the family that siblings occupy, much like the niches different species of animals occupy in an ecosystem – argues that only children are free to occupy any niche.

"What Sulloway is trying to explain here is the embarrassing fact – embarrassing not just to him but to all believers in the nurture assumption – that only children do not differ in any systematic way from children with siblings," Harris says. "These children have missed out on the experiences that play such an important role in Sulloway's theory: they haven't had to compete with their siblings for parental attention, and they haven't had to learn how to get along (or not get along) with a bossy older sister or a pesky younger brother. And yet their personalities are indistinguishable from those of children with siblings."

For his part, Sulloway is unapologetic. "Judith Harris does not really have a point," he says. "Although she has critiqued my meta-analysis of the birth-order literature, and has done so in a seemingly convincing fashion, she made no attempt to reanalyse these data, taking [my] criticisms into account, to see whether such criticisms actually made any difference in the overall results. Typically in science if someone has a valid objection to another researcher's methods and results and thinks such criticisms make a difference, they then do the appropriate reanalysis to show this is indeed the case."

So, with such inflammatory accusations and counter-accusations flying between two of the leading exponents in the field of personality and birth order, what are we to believe when it comes to the supposed advantages and disadvantage of being the eldest, the youngest, the middle or the only child?

Professor Nigel Nicholson of the London Business School, and author of a forthcoming book on birth order called Family Wars, believes that Sulloway has a point with his niche theory of sibling rivalry. "There's certainly something in it, but the evidence seems to suggest that birth order has a negligible impact on measurable personality," Nicholson says. "You need different strategies to survive in a family, and siblings who are disadvantaged in some way have an incentive to rewrite the rules to their advantage, which is why later-borns may tend to be more radical," he says.

"If there is any evidence of differences in IQ between children of different birth order, it is very, very slim. But then it is pretty obvious that the more attention and the more investment you can afford to put into a child's development, the more you'll get out."

When Nicholson sees his five children interacting, he sees it as a drama full of actors. "Do they carry those strategies forward in life? I don't know. I think we have scripts of our own lives, and they are partly written in childhood. The script says, 'You are the bold one,' or whatever, and you carry it forward in life. Those scripts are pretty powerful – if you believe them."

The Kennedys

There were nine of the famous Kennedy siblings, who were all children of Joseph, US ambassador to Britain during the 1930s. The eldest, Joseph jnr, was the apple of his father's eye: a clean-cut, gung-ho war hero killed during a 1944 WWII bombing raid. The most famous of the middle brothers, John, was the charisma-laden president who was a gifted diplomat, but nonetheless had several character flaws – and once bedded Marilyn Monroe, before being assassinated. Typically, the youngest of the brood, Edward (known as "Teddy"), never seemed to settle down: a Massachusetts senator since 1963, he has been married twice, with three children from his first marriage and two stepchildren from his second.

The Mitfords

Even by the standards of the British aristocracy, the Mitfords were an eccentric bunch. Nancy, the eldest daughter of the second Baron Redesdale, was the sucessful, professional older sibling, a chronicler of upper-class life, biographer of Madame de Pompadour and Voltaire, and one of the Bright Young Things on the London circuit of the interwar years. Then there were the "problem" middle sisters, Unity and Diana. Taking her inherited right-wing politics to an extreme, Unity befriended Hitler, who described her as "a perfect specimen of Aryan womanhood". When Britain declared war on Germany, a distraught Nancy shot herself. Diana, for her part, married the fascist Sir Oswald Mosley, who spent the war years in prison. The youngest Mitford, Deborah, known as "Debo", fits the profile of the creative last born. Having married the Duke of Devonshire in 1941, she has written several books on the restoration of the family seat, Chatsworth House. She has recently founded successful Chatsworth shops in London and Derbyshire.

The Gallaghers

You would be forgiven for thinking that the Gallaghers were a two-sibling family. Warring brothers Liam and Noel have hogged the familial limelight as pioneers of Britpop, and carved a reputation in the tabloids for rock'*'roll excess. Liam, the youngest son of Peggy and Tommy Gallagher, fits the bill as the charismatic livewire last-born, while his older brother Noel, more level-headed, was dubbed by NME "the wisest man in rock". But let's not forget the eldest member of the clan – Paul. Even as a child he was the quiet, pensive one; Liam once unkindly called him "the weirdo of the family", and he developed a stammer. In adulthood he was content with relative anonymity, managing bands in Manchester and studiously keeping a scrapbook of cuttings about his superstar younger brothers. In 1996, he co-wrote the most controversial Oasis biography, Brothers: From Childhood to Oasis.

The Windsors

The Queen's offspring have never, as far as we know, taken IQ tests. But comparing their paths seems to support theories on sibling development. True, Charles's position as heir to the throne thrust upon him more responsibility than the average first-born must endure, but his business success – his Duchy of Cornwall interests are worth an estimated £550m – support the theory that oldest siblings are hard working and conscientious. Then there's middle-born Andrew, whose semi-successful military career, doomed marriage with Fergie and "Playboy Prince" label indicate a confused role as spare-to-the-heir. Tail-end Edward is the most artistic of the clan; after a degree in history he dropped out of the Marines and made forays into theatre and television.

The Bushes

If proponents of the new theory on sibling development had to pick which Bush would become President, they'd go for the eldest, who, in theory, is most likely to hold a professional position. George "Dubya" is indeed the first child of George and Barbara Bush and – despite dalliances with drink, girls and draft-dodging in his youth – proved a reliable family man and a canny businessman, making millions from Texan oil interests. Like many a middle child, his younger brother Jeb struggled to settle down but later became Governor of Florida. Then there's poor Neil, who suffered from dyslexia and who, as a board director of Silverado Savings and Loan, became the public focus of a 1980s crisis that cost taxpayers a reported $1bn. In a recently leaked letter to his wife, Neil said: "I've lost patience for being compared to my brothers."

The Jacksons

Katherine and Joseph Jackson spawned their clan over 16 years. The eldest was Rebbie, who (in keeping with scientific expectation) has been studious and conscientious, and avoided the turmoil that engulfed many of her siblings. Rebbie has been married to her childhood sweetheart for almost 40 years, and in 1965 followed her mother into the Jehovah's Witness faith. Moving to the middle, we reach Jermaine, whose peacemaking skills were evident when he supported a troubled middle brother, Michael, during the latter's 2005 child abuse trial. He also shows an inability to settle, having tried his hand at singing, reality TV (Celebrity Big Brother), Islam (he converted in the 1980s), theatre and marriage (he is on his third wife). Janet seems typical of a last-born – the extrovert rebel who aims to please but often comes a cropper.

Additional reporting by Simon Usborne