The order in which we were born influences in some way our personality and our way of relating. The same happens with our children, to whom being the firstborn, the medium or the small determines their role in the family and their way of being. For example, the firstborn have always been traditionally more responsible than the secondborn.
However, the influence of the order of birth on the personality could have been exaggerated in light of the results of some recent analyzes. At least, what seems to matter most to forge our personality is not so much the order in which we are born, but how our parents treat us (depending on that birth order or not).
Alfred Adler, an Austrian psychotherapist of the late nineteenth century and founder of individual psychology, as well as a disciple of Sigmund Freud, was one of the first to suggest that the order of birth leads to differences in personality. Adler considered that the firstborn were neurotic, because they do not have to share their parents for years and, essentially, their privileges begin to decline once a brother arrives. He also considered older children as obedient and sometimes conservative. On the other hand, younger siblings are ambitious, while middle children have an optimal position in the family and are characterized by emotional stability.
The explanation underlying Adler's ideas seems obvious: each child occupies a certain niche within the family and then uses their own strategies to thrive in life. However, current evidence suggests that the period in the life of the parents, their status and resources, affect the way parents raise their children, which probably affects their personality.
Thus, things are more complicated than it seems: our upbringing is an inseparable mixture of genes and environment, and trying to measure any of these areas is, at least, thorny.
The idea that the birth order forges our personality in a certain way is reflected even in current educational guides because there is enough scientific literature that supports such claims. However, the problem of these studies are several. First, the older brothers were not only born first, they were also simply older. That is, when studied they are more mature and more psychologically trained than their younger siblings, which could alter the measurements of any study in this regard.
Another methodological flaw in many of these studies lies in the fact that only one person judges their own personality and that of their siblings, that is, the older brother is asked about all this. This detail is important because the self-perception and perception of others can sometimes differ considerably. Further, subjects may have unconsciously incorporated the cliche of obedient and cosmopolitan older brothers; Even parents themselves may have adopted this widespread stereotype if asked about their children's personality.
Another one: Being the size of the family influences. Families with more children are usually of lower socioeconomic classes. Thus, for example, it may be significant that many astronauts are firstborn, but it is not so important if we analyze, for example, that they can belong to higher socioeconomic classes where there are fewer children (and therefore the probability of being primitive is greater ).
All these biases were some that wanted to isolate researchers led by the psychologist Julia Rohrer, from the University of Leipzig in Germany, who evaluated data from more than 20,000 respondents from Germany, the United Kingdom and the United States. They compared the personality profiles of the brothers, but also of people with different birth orders who had never met each other. What they discovered was that there were no significant differences in personality.
And the larger the sample size, the lower are the distinctive features of the firstborn, as this other 2015 study conducted by the psychologist suggests Rodica Damian and his colleague Brent W. Roberts, both at the University of Illinois at Urbana-Champaign, and that included 377,000 high school students.
In other words: we are facing a causal jungle, a very dense jungle of huge clusters of interactions. Therefore, your position in the family can affect your personality, but it is not always the case, and it also depends on the family we analyze, its socioeconomic position and, naturally, your genes. Not counting other no less important influences, such as friends (and all peers or the like), the way parents treat their children based on the stereotype that exists about how the firstborn are (a sort of self-fulfilling prophecy), and a whole string of factors that eclipse those watertight compartments so clear and evident that Adler proposed.