The honest answer to this question has to be: we don’t really know. I am no specialist in this field, and even the specialists don’t seem to have a clear answer to the question.
Nevertheless, we thought it’d be interesting to explore some of the research that has been done on the topic – the claims that have been made, and the implications of them. You can make up your own mind as to what’s true and what’s not.
1. Second-Borns are More Rebellious
It’s a fairly well-known assumption that first-borns are more conscientious and socially conservative than their second-born relatives. This argument was put forward by Frank Sulloway in his book Born to Rebel. Sulloway argues that later-borns are more agreeable, extraverted, and nonconformist than their first-born counterparts, and that these traits continue to shape their lives well into adulthood. You can see some of his arguments here.
Other studies have supported Sulloway’s claims. One study found consistent support for the hypothesis in self-reports by both youth and adult respondents. First-borns scored higher on conservatism, conscientiousness, and achievement orientation. Later-borns scored higher on rebelliousness, openness, and agreeableness.
These studies face problems because of the classic difficulty of disentangling correlation from causation. For instance, while we can find a statistical correlation between first-borns and those who become astronauts, it does not follow that those individuals are more likely to become astronauts because they were first-borns. It may simply be a result of the fact that highly-educated, high-socio-economically-advantaged families are disproportionately likely to have fewer children, and that astronauts disproportionately come from rich, well-educated families. Or it may legitimately be a result of first-born-ism. From the data alone, we don’t really know for sure.
2. First-Borns are More Intelligent
One curious observation which has frequently been made is that first-borns tend to score higher on IQ tests than their younger counterparts. In fact, within families there seems to be a trend for IQ to drop a couple of points with each child down to the third or fourth sibling, at which point it levels out. (Of course this is a trend, not an absolute…there are plenty of families where they younger kids outsmart their elders.)
Perhaps the most famous explanation for this was put forward by the social psychologist Robert Zajonc. His Confluence Model posited that first-borns mainly have adult influences around them in early years, and spend their initial years interacting in a highly intellectual family environment (as opposed to being surrounded by other toddlers). As other children arrive, the first-born also has the role of acting as a teacher to the younger sibling, and this “tutor effect” is said to further enhance the IQ of first-borns.
While the notion that first-borns have a higher IQ than their younger siblings has proven controversial, it has found some support from recent research. In 2007, for instance, Norwegian epidemiologists Petter Kristensen and Tor Bjerkedal published work showing a small but significant negative correlation between birth order and IQ. In other words, the younger one is in the birth order, the lower one’s IQ is likely to be.
While this question is clearly still controversial, the sheer size of this study's sample (about 250,000 individuals) and its rigorous controls for family size make it very convincing. A number of researchers are now taking the IQ theory seriously.
3. Like Seeks Out Like
It’s a folk truth that middle siblings seek each other out, and that elder siblings do the same.
In 2009, however, some scientific research seemed to point for the first time to the suggestion that there was truth in this tale. Joshua Hartshorne and others identified that first-borns were indeed more likely to associate with first-borners, middle-borns with middle-borns, only children with only children, and so on. Incredibly, their findings showed not only who people choose to be friends with, but who they’re likely to select as spouses.
Because the researchers controlled to show an effect independent of family size, the finding is unlikely to be an artefact of class or ethnicity. It may be a result of the fact that like really does attract like in relationships, and that somehow birth order makes you like someone in the same family position.
All a load of old cobblers?
Despite the new research, many people continue to doubt that birth order has any significance on personality. Some people find it hard to believe that any correlation could exist over such a large scale.
What do you think? Is birth order a real factor to be considered, or does it not really make much of a difference? Let us know your thoughts and experiences in the comments below.