Successful first-borns, creative stragglers?

Sibling myths: Part 2

Siblings are not as similar in nature as you might think. But where do the differences come from, given that children of the same parents share half of their genetic make-up on average and usually grow up in the same environment? The Viennese psychotherapist Alfred Adler (1870-1937), founder of individual psychology, already suspected that the order of birth was the cause of differences in character.

He considered first-borns to be neurotic, as after the first few years in which they do not have to share their parents with anyone, they are virtually «dethroned» by the second-born. At the same time, as «guardians of order», the eldest are dutiful and sometimes conservative.

According to Adler, the eternally inferior nestling develops a strong sense of ambition. Middle children, on the other hand, have the most favourable position in the family and are characterised by emotional stability.

Adler himself was the second of seven siblings. The American science historian Frank Sulloway, who combed the history books at the end of the 1990s for first-born leaders and rebellious latecomers, took a similar view.

According to Adler, the eternally inferior nestling develops a strong ambition.

Among the late-born, he found lateral thinkers and revolutionaries such as Charles Darwin, Karl Marx and Mahatma Gandhi; he saw typical first-borns in Stalin and Mussolini. His explanation: each child occupies a specific niche within the family and then uses their own strategies to master life.

First-born and only children have less reason to quarrel with the status quo and identify more strongly with the world view of their father and mother. Younger siblings are less certain of their parents' favour and are therefore more likely to take alternative paths in life.

Questionable investigations

Such categorisations are popular because they make intuitive sense and you can always find an example of the sensible big sister or the rebellious little one in your circle of friends. This is why Adler's words still regularly appear in parenting guides and continue to echo in the minds of parents.

Some studies have also confirmed the theory that the psychological starting conditions differ depending on the sibling's position and help to shape their personality.

However, some of these studies used questionable methods. Members of the same family were often asked to assess themselves in terms of extraversion, openness to experience, conscientiousness, agreeableness and neuroticism, i.e. emotional instability.

The catch: the survey only took place at a single point in time. The older siblings were therefore not only born first, but were also older. It is well known that young people become more conscientious as they get older and this could account for a large part of the effect.

Another methodological flaw was that only one person was asked to judge their own personality and that of their brother or sister, because self-perception and the perception of others can sometimes differ considerably.

In addition, the test subjects could have unconsciously incorporated the cliché of the dutiful older person and the cosmopolitan younger person into their assessment and thus brought about the expected result themselves.

There are no systematic differences in nature

Scientists have now analysed large, cross-national data. And lo and behold: if you look at such samples and compare different families with each other, the effect of sibling order on personality disappears almost completely.

Researchers led by psychologist Julia Rohrer, then working at the University of Leipzig, analysed data from more than 20,000 respondents from Germany, the UK and the USA.

They compared the personality profiles of siblings, but also of people with different birth ranks who had never met. The Leipzig psychologists did not discover any systematic differences in character.

Researchers have to proceed with particular caution in such studies, because in addition to age, another factor is intertwined with sibling position: the size of the family. A child from a family of four has a 50 per cent chance of being a first-born; the more siblings, the lower the probability.

The fact that a disproportionate number of astronauts are first-born does not necessarily indicate that first-borns have special astronautical qualities, but perhaps simply that families with many children are less likely to produce astronauts.

In order to disentangle these influences, Rohrer and her team also analysed large families. Here, however, there was also no effect of sibling order.

Influence of sibling order on character is overestimated

The larger the sample, the more likely it is that even very small effects can be detected. For example, a US study by psychologist Rodica Damian and her colleagues from the University of Illinois at Urbana-Champaign, which looked at 272,000 high school students, found a statistically significant correlation between birth order and personality.

The first-borns actually tended to be more conscientious, less sociable and more willing to lead. Contrary to expectations, they also proved to be more compatible and emotionally stable than the adolescents with older siblings. However, the influence of sibling position was found to be very small.

The firstborns actually tended to be more conscientious, less sociable and more willing to lead.

The effect size, a statistical measure that illustrates the practical relevance of a factor, was just 0.02. By comparison, the socio-economic status of the family reached values of up to 0.4 in the same study. The importance generally attributed to sibling position in shaping character is exaggerated, the authors conclude.

«It is quite possible that the position in the sibling line shapes the personality. But not in the same way in every family. In other words, there may be an influence, just not a systematic one.» This is the opinion of Frank Spinath, Professor of Differential Psychology and Psychological Diagnostics at Saarland University, Germany.

It is quite possible that the position in the sibling line shapes the personality.

«Nevertheless, other influences weigh more heavily when it comes to the character differences between siblings. In addition to genes, the so-called non-shared environment plays a role. For siblings who grow up in the same family, this includes their circle of friends, for example.»

What's more, parents do not treat their children in the same way - regardless of their birth rank. Studies show that parents react sensitively to the innate temperament of their offspring and adapt their parenting accordingly.

IQ of first-borns slightly higher

However, one difference is considered certain: first-born children achieve a slightly higher IQ on average than their younger siblings. It is only a matter of a few IQ points, which is probably hardly noticeable in everyday life.

Nevertheless, the oldest tend to complete their education with a higher degree and are more likely to opt for traditionally prestigious degree programmes such as medicine or engineering, which ultimately has an impact on their bank account.

How does this intellectual advantage come about? Adler may be right here: the undivided attention that the first child receives in the early years of life apparently promotes cognitive abilities. This advantage is already evident at the age of two.

The Norwegians Petter Kristensen and Tor Bjerkedal skilfully demonstrated that the difference in intelligence is not due to biological factors - some researchers suspect physical conditions during pregnancy.

The likelihood of older people being slightly more intelligent is higher than the likelihood of younger people outperforming their older siblings.

They tested children whose older siblings had died at an early age. The assumption: although these children were biologically younger siblings, they took on the role of the first-born in the family. Compared to other younger siblings, they achieved better results in intelligence tests.

A small consolation for all nestlings: such findings do not allow any reliable conclusions to be drawn about the distribution of intelligence in one's own family. Only the probability that older children are slightly more intelligent is higher than the probability that younger children outperform their older siblings.

This article first appeared in «Spektrum Psychologie», 2/2019 (March/April)