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From placenta to play centre

Serial killers, Prime Ministers and divorcees

Few people can claim to have the scientific pedigree of Sir Francis Galton (1822 - 1911).

Both of Galton’s grandfathers - Samuel ‘John’ Galton and Erasmus Darwin - were key thinkers during the Midlands Enlightenment of the late 18th Century, and were members of the exclusive Lunar Society, a gathering of prominent gentleman who would meet to discuss exciting developments emerging from this golden era of science. Galton also had a couple of highly capable cousins, first with Douglas Strutt Galton, an engineer who worked closely with Florence Nightingale to improve hospital safety, and second with Charles Darwin, who also knew a thing or two about science.

The young Francis was somewhat of a prodigy, having learnt to read by the age of 2, write letters by age 4, and freely quoting Shakespeare by the age of 6. After obtaining both medical and maths degrees, he embarked on a career that saw him become a polymath of extraordinary proportions. He is credited with developing the first classification system for human fingerprints, devising the first meteorological map, conceiving the statistical concepts of correlation and regression, and even inventing the dog whistle.

Throughout his expansive career, one of Galton’s enduring preoccupations was to understand, as he described in his elegant Victorian prose, ‘the pre-efficients of eminent men’. Galton understood that there was considerable variation in human ability – quite an achievement in 19th Century England where social class trumped everything - and he sought to determine whether intelligence was due to ‘nature or nurture’ (a phrase which he coined).

One of Galton’s most fascinating studies was to ask 180 Fellows of the Royal Society of London - the most learned society of the day - to complete an autobiographical questionnaire (a research method which he invented). His goal was to understand whether their interest in science and their achievements were innate or due to the encouragement of others.

His observations from this study were published in 1874 in the splendidly-named tome, English Men of Science. (Women were not eligible to be admitted to the Royal Society until 1902). One of the most curious findings of the study was that the Fellows were more than twice as likely to be the eldest son in their family, than the youngest. Galton wrote:

‘the elder sons have, on the whole, decided advantages of nurture over the younger sons. They are more likely to become possessed of independent means, and therefore able to follow the pursuits that have most attraction to their tastes; they are treated more as companions by their parents, and have earlier responsibility, both of which would develop independence, both of which develop independence of character.’

Whether Galton identified the true origin of genius through this work is questionable - he also found that Fellows were more likely to have parents who had the same coloured hair – but his research spawned an idea that has lasted to the current day, that the order in which we are born can influence a life’s course.

Francis Galton: A man of extraordinary talent…and breath-taking sideburns.

Birth order

It is now the stuff of popular culture that birth order is somehow determinate of the kind of person we will be.

First born children, we are told, are the leaders, and are over-represented in the lists of US Presidents (Bill Clinton, George W Bush) and Nobel Prize winners (Francis Crick, James Watson). First born children are also born with a certain je ne sais quoi that makes them more likely to be serial killers (Charles Manson, Jeffrey Dahmer), astronauts (21 of the first 23 US astronauts were the first-born male in their family), and James Bond actors (Sean Connery, Roger Moore, Timothy Dalton).

Last born children, on the other hand, are the non-conforming rebels, unbridled by over-bearing parents and free to explore their creative sides. The comedic line-up of Jim Carrey, Drew Carey, Eddie Murphy, Rosie O’Donnell and Billy Crystal are all the youngest of their respective broods.

Finally, middle children are the negotiators, stuck between the leader and the rebel, these children must rely on their charisma (Madonna) and charm (Princess Diana) to get by in the world.

Birth order taps into similar gross generalizations that make astrological signs such tongue-in-cheek fun. They allow us to parse our daily calamities and triumphs (and those same events of others) according to the invisible hand of the universe: ‘it’s not my fault I’m pushy, I’m a first-born/Aries!’. But how much scientific evidence is there behind this proposition?

Birth order and IQ

In actual fact, there has been an astonishingly large amount of research that has examined the enticing idea that our level of achievement is influenced by the order in which we were born. Galton got the ball rolling in this area, but it was Lillian Belmont and Francis Marolla who first examined this in a rigorous way.

In their 1973 study, Belmont and Marolla studied the intelligence of around 400,000 men born between 1944 and 1947, who fronted for military service at the age of 19. The results of the IQ test were then grouped into scores, ranging from a high score of 1 to a low score of 6.

What they found was startling. For each type of family, IQ was found to consistently decrease as birth order increased, so that in a three-child family, for example, the first born child was more likely to have a higher IQ than the second-born child, who in turn had a higher IQ than the third-born child. Figure 1 shows the pattern of their findings.

Figure 1. Average IQ scores ranging from 1 (high) to 6 (low) for men according to their birth position.

This finding made world headlines. “Birth order can make a difference in IQ”, proclaimed the New York Times, and you could almost hear the gloating of the older siblings. Yet, while this study provided clear evidence for small IQ differences according to birth order, the research did not seek to understand what may cause such an effect.

Two broad scientific theories reign in this area.

The first is social in origin, claiming that any effect of birth order relates to the interaction patterns that develop between family members. First-borns, the theories go, are parents’ first experience with child-rearing, and they therefore adopt a highly protective parenting style, which may lead to more conscientious and achievement-oriented children. By the time the second- and third-born child comes along, the parenting game is old hat, and a less protective parenting style is enacted, perhaps leading to more rebellious children - either that, or the parents are just too busy!

The second line of thought is that there may be biological differences between first- and later-born children. One hypothesis is that pregnancies to male fetuses in particular, may create an immune response from the mother. The probability of these maternal antibodies influencing the brain of the developing fetus increases with each advancing pregnancy (and thus so does the chances of IQ being disrupted).

Cause(s) of birth order effect?

Petter Kristensen and Tor Bjerkedal sought to understand the potential causes for the birth order effect observed by Belmont and Marolla when they examined the IQ tests of Norwegian army conscripts.

The researchers were particularly interested in whether IQ varied according to a child’s biological and social rank within the family. While these ranks are the same for most children, under certain circumstances the ranks differ. For example, a second-born child will have a biological rank of 2. However, if that child has an older sibling who has died, and they are therefore raised as the oldest living child, their social rank is 1.

Kristensen and Bjerkal surmised that if the birth-order effect on IQ was determined by the social niche, then these children would have the same IQ as first-born children in families where no siblings had died. However, if the effect was biological in nature, then their IQ would show a similar small decrease, in line with other second-born children.

It was this former finding that was observed. The death of an older sibling meant that a later-born child moved up the social rank, and consequently they did not show the small decrease in IQ observed in other second-born children. The birth order effect, the researchers concluded, depended on the social rank in the family and not birth order – it is just that in most families birth order and social rank coincide.

A big word of caution about this finding is the size of the effect, which is small - very small. The decrease in IQ from a first-born to a second-born child was around 3 points. To put this in context, most researchers believe three points is approximately the standard error of measurement for IQ tests. Furthermore, the findings do not mean that every first born will be three IQ points more intelligent than every second-born, rather these differences are trends that only emerge after studying the population at large.

Galton made an astute observation about birth order in his study of the Royal Society Fellows. Of course, what also emerged from the research was that these English Men of Science were also overwhelmingly English men of privilege.

Most Fellows were born in large cities around the United Kingdom, and the majority had fathers who were men of influence: Nobleman, private gentleman, army or naval officers, doctors, lawyers or members of the clergy. Nearly two-thirds of the Fellows were university educated, and one-third of these at Oxford or Cambridge (very much schools for the privileged in the 19th Century). As Galton himself put it:

‘There can be no doubt but that the upper class of a nation like our own, which are largely and continually recruited by selections from below are by far the most productive of natural ability. The lower classes are, in truth, the “residuum”.’

Suddenly, the effect of birth order on life achievement doesn’t seem to matter all that much.
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