Kids are mysterious, even to their parents. (Perhaps especially to their parents.) Why is the oldest so controlling? Or the youngest such a terror? Dismissing the potential effects of our neurotic parenting, we ascribe many of our kids’ traits to the self-evident truth of birth order.
Unfortunately, there is little science to back up that truth.
In a new commentary ”settling the debate” on birth order, Rodica Damian of the University of Houston and Brent Roberts of the University of Illinois usefully summarize research on the topic to date. In a mercifully jargon-free, two-page review, the academics stress that ”scientific evidence strongly suggests that birth order has little or no substantive relation to personality trait development and a minuscule development of intelligence.” The commentary was published today (Oct. 26) in the Proceedings of the National Academy of Sciences.
Hundreds of studies have been conducted to try and link where we are born in a family and who we become. In the Western world, the assumption is that older kids are more neurotic, intelligent, controlling, outgoing, and conscientious while younger kids are more sociable and generally less high-strung. From an evolutionary standpoint this seems logical: the first born gets the advantage of time—a few precious years without competition—allowing him or her to thrive. The later-borns have to compete for a place in the family and find a niche most likely to maximize parental investment.
But Damian and Roberts dismiss birth order as a factor in personality or smarts, drawing their conclusions largely from two comprehensive studies on birth order published in the past year.
The first study, published in the Journal of Research in Personality, was conducted by Damian and Roberts themselves. They tested 377,000 US high school students to see if five characteristics—extraversion, emotional stability, agreeableness, conscientiousness, and openness to experience—and intelligence are determined by birth order. The study is a “between family” design, meaning that it looked at kids in different families who fell in the same birth order. It controlled for things such as age, sex, number of siblings, socio-economic status, and family structure. It is the largest US study of its kind, and found no significant connection between birth order and personality traits, and only a very small difference in intelligence.
Another study published in the Proceedings of the National Academy of Sciences looked at birth order in 20,000 adults in the US, UK, and Germany. The research, conducted by a trio of German academics led by Stefan Schmukle of University of Leipzig, addressed some of the shortcomings in previous studies: it tested both between families and within the same families, across more than one country, and it did not rely on the input on just one sibling. It controlled for gender and large age gaps. It also concluded that birth order has a tiny effect on intelligence and no effect on personality.
And so, Damian and Roberts write, the persistent belief that birth order determines much of anything deserves to be ”laid to rest as viable explanation for the fascinating differences we see across people and siblings in the typical ways in which they feel, think, and behave.”
Dream on. Thanks to the desperation of parents looking to assign logic to their children’s illogical personalities, few of us are likely to let science override the powerful evidence we observed at breakfast this morning.
Damian and Roberts explain this intellectual intransigence as a simple human failing. People are ”susceptible to weighing anecdotal information more heavily than data-driven findings,” they write.
Tell that to Sigmund Freud. In the 1920s, philosopher and psychiatrist Alfred Adler, the second of six children, posited that first- and last-born children were neurotic due to their constant struggle for success and superiority. Middle children, like himself, were better adjusted: healthier, easy going, and rebellious. Freud, a neurotic oldest child, vehemently disagreed and stoked “one of the most heated scientific disputes of all time.” The debate ended with Adler resigning from the Psychoanalytic Society and founding an entirely new branch of psychology, via the Society for Individual Psychology.
The discussion has never really died down since then, despite researchers’ best efforts. Birth order as destiny is beautifully predictive and explanative. We embrace the clean, if unscientific, framework because of our natural inclination toward confirmation bias: we look for evidence to confirm what we want to believe and disregard facts that upset our hypothesis. Parenting is a maddeningly unscientific process and applying such cold logic allows us to construct a (false) sense of control.
But birth order is a subject in which “personal experience will be wrong and the truth can only be discovered through good scientific reasoning and investigation,” Damian and Roberts conclude. “The problem in this case is that data-driven findings are seldom as compelling as personal experience.”
For now, I’m sticking to my truths: I am the best-adjusted in my family because I am the youngest.