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The science of siblings

Are first-borns really natural leaders, and younger kids rebellious creative types? Does your position in the family affect anything other than the quality of hand-me-downs you score?

Sibling issues have been around since about page three of Genesis, and while pet theories on the impact of siblings on our personalities abound, the evidence is way short of convincing.

But for general indicators of success in life, your position in the family line-up has a clearer impact and the best place to be is number one.

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Birth order, brains and bank balance

As well as hogging the big room and first dibs on hand-me-downs, oldest kids have an advantage over the rest of us when it comes to educational achievement, income and employability.

A massive longitudinal study of the adult population of Norway from 1986-2000 has just re-confirmed what the literature's been saying for years: first-borns and those with no siblings do better at school. And not just a bit better — they outperform their younger siblings by the equivalent of having had an extra year of schooling.

And the differences don't stop there. While special mention wasn't made of ninth-borns, younger Norwegian sisters miss out all round. As adults they earn less, are less likely to work full-time and are more likely to become teenage mums.

Theories on why numero unos do better are usually along the lines that the older child acts as a teacher to the younger kids, and learns useful skills in organising information (not to mention browbeating & general bossing around). Theorists do concede that lowering of parental expectations and levels of cash by the time the younger kids arrive could also play a part.

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In sickness and in health

If you're starting to resent your older sibling's chances for life success, let it go. For all their brains and bucks, first-borns draw the short straw when it comes to risk of disease. Eldest kids are at higher risk of developing allergies, spina bifida and (for males) schizophrenia.

But it's not all bad news for first-borns in terms of health-prognosis — having lots of grotty younger brothers and sisters might protect you from getting multiple sclerosis (MS) later in life. A recent Australian study found that living with younger siblings reduces your risk of developing MS by 88%.

The current thinking is that thanks to the dubious personal hygiene of younger siblings, older kids are regularly exposed to childhood bugs, giving their immune systems a workout that will help fight the infections associated with MS down the track. (Ebstein Barr Virus, which causes glandular fever, is strongly associated with MS).

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But what about personality

Health, wealth and wisdom aside, your position in the family has no real effect on your adult personality no matter what the pop psychologists say.

It's almost a hundred years since Alfred Adler (middle child and contemporary of Freud) first came up with the idea that birth order is a major factor in shaping the person we become.

Adler's heart went out to first-borns, whom he figured never quite recovered from the shock of losing their princely status on the arrival of some younger, cuter version of themselves. Youngest kids, he believed, were headed for inferiority complexes with their comparative lack of freedom and excessive pampering. Middle-children, like Adler himself, were thought to have things the easiest. (Adler's work clearly pre-dates Jan Brady's seminal findings in the 70s).

Since then, countless PhDs and pop psychology books have been devoted to teasing out the personality traits associated with eldest, youngest and middle-borns. And according to a landmark study in 1983, all that's missing from the birth-order/personality link is any basis in fact.

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Only in the family

When Swiss researchers Cecile Ernst and Jules Angst analysed hundreds of post-war studies on birth order and personality their findings rocked the world of psychology.

They found that as adults, first-borns and later-borns perform no differently in standard personality tests. So you can't pick someone's personality based on their position in their family - first-borns are no more likely to be aggressive/domineering/narrow-minded, and last-borns don't fall neatly into the rebel cluster. With one exception...

Ernst & Angst found one group of studies where all the 'blame it on your birth order' books held true: In studies where family members rated each other's personalities, the birth order effects were plain as day!

So Adler was right — our birth order does have lasting impacts on our personality, but only in the company of the people we grew up with. This not only explains a lot about family Christmases, it makes sense from a developmental point of view.

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Position matters everywhere

It's critical for kids to figure out their personalities in line with their position in the family. The oldest sibling will always be bigger and know more. They're not the kind of person you want to get off-side, so younger siblings learn to work the system by being more agreeable, sympathetic and open-minded. And those older siblings know they can get away with being bossy — it makes up for the extra responsibility and cut in the love quota they scored when Junior arrived.

But as important as it might be to find ourselves in our family, we've also got to elbow our way through the greater world as well. Every time we become part of a new group — playground, school, soccer team, boardroom — we find our position within it.

And thankfully, from what Ernst & Angst (and a wealth of other studies) have shown, the behaviours and personality traits we learn in our family don't automatically transfer to our lives in the playground or beyond — so we're not stuck with our family persona outside the home. Our adult personalities are a combination of the traits we develop in our many environments, and they vary with the company we keep.

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Who needs evidence?

Of course developmental psychology being the hotbed of academic argie bargie that it is, not everyone is buying Ernst & Angst's line. Most notably, scholar, author and recipient of a MacArthur Genius Grant (and they don't hand those out in cereal boxes), Frank Sulloway.

In his 1996 bestseller Born to Rebel, Sulloway re-examines some of the data from which Ernst & Angst drew their conclusions. His findings — that birth order is indeed a factor in adult personality — are about as different from those of his Swiss colleagues as you can get without actually playing the record backwards. While his failure to provide details of the studies he analysed has led to much slagging off in the psychology community, there's been no noticeable slump in his book sales.

So the halls of developmental psychology remain a little divided, books on blaming your foibles on your family continue to sell, and the birth-order/personality edebate rolls on, albeit it at a reduced pace.

The research doesn't back it up elsewhere, but if you're heading home for Christmas it might help to bone up a few Adlerian facts about who and what you are. You might have gone completely against type in every other area of your life, but when it comes to family gatherings, science and your siblings will keep you in order — take it from number nine.

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