Among the canon of pop psychology theories, birth order theory is one of the longest-lived. There is an intuitive, almost visceral, sort of logic to the theory that where we fall in sibling chronology, or whether we have siblings at all, shapes our personality.

“[I’m a] typical oldest child for sure,” says Chennai-based S., a mid-30s professional with two younger siblings, who requested anonymity out of respect for their privacy. “[I] definitely feel the weight of responsibility, parents’ expectations, trouble delegating.”

S.’s middle sibling, on the other hand, “definitely felt overlooked and fought for attention. [My] youngest sibling — parents definitely left them a lot more to their own devices when growing up, fewer rules and curfews. More pampered, spoiled.

“[It] all sounds so cliché.”

It does — and yet, research has repeatedly debunked the idea that the birth order of siblings (or lack thereof) influences personality in a universal or measurable way. In other words, there’s no such thing as ‘typical oldest sibling’ or ‘typical only child’ behavior.

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Birth order theory was first developed by Alfred Adler, an Austrian psychotherapist in the late 1800s and early 1900s. It goes something like this: Firstborn children grow up to have similar personality traits as other firstborn children, youngest children have similar personalities across families, middle children have fundamentally like characteristics, and only children have similar traits. Adler’s breakdowns of the characteristics of each will sound very similar to stereotypes that still abound more than a century later: Eldest children are bossy, conventional, and strive to be their parents’ helper; middle children are complacent; youngest children are ambitious but spoiled; only children like being the center of attention.

The theory that birth order affected personality in some universal way gained prominence and cult-pop psychology status in the mid-90s, when Frank J. Sulloway, PhD, an American psychologist, published Born to Rebel: Birth Order, Family Dynamics, and Creative Lives, according to Scientific American. In the book, Sulloway takes Adler’s theory one step further by explaining that family dynamics influence personality in early childhood and children carry into adulthood the strategies they develop to navigate their niche within a family. He backed up his assertion by applying it to historical figures: bold thinkers and revolutionaries, like Charles Darwin or Mahatma Gandhi, tended to be younger children, he found, while authoritarian leaders, like Joseph Stalin, tended to be eldest children.

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In the decade preceding Sulloway’s book, however, psychology started coalescing around a measure of personality known as the Big Five traits. While certainly not the only theory of personality, it is, now, a fairly established measure of fundamental nature, the building blocks of which are: extraversion (or, extroversion), agreeableness, openness, conscientiousness, and neuroticism.

Early research seemed to support Adler-by-way-of-Sulloway’s theory. But these studies were often small and failed to control for a host of influencing factors; for instance, per Scientific American, oldest siblings may simply appear to be more conscientious because they’re, well, older, and other research has shown conscientiousness increases with age. Or, for instance, the widely cited fact that NASA astronauts tend to be eldest children fails to take into consideration that the probability of a child being the eldest is higher in small families (50-50 for a family with two children; 30-60 for a family with three; etc) — muddying the research waters, therefore, as to whether it is the birth order, the small family size, or the circumstances (smaller families correlate with more educated, higher socioeconomic classes) that influenced their pursuit of a conventionally high-achieving career.

Later research, with much larger sample sizes that allow scientists to generate more conclusive results, has since debunked any such link between birth order and the Big Five traits.

“There seems to be a growing consensus that birth order does not influence personality in a way that can be measured in adulthood,” Tomas Lejarraga, PhD, director of the Decision Science Laboratory at Spain’s University of the Balearic Islands, told the Washington Post. Lejarraga is a co-author of recent research exploring birth order and risk-taking behavior. At the start of the study, he and his co-authors hypothesized that later-borns (anyone with one or more older siblings) would show a tendency toward more reckless and adventurous behavior, since parental attention is divided between them and their older sibling(s) — unlike first-born children, who are for at least some of their formative years the sole focus for parents.

Lejarraga and the team’s study is one of the most rigorous available, comprising, really, three studies. In the first, he and his co-authors had 1,500 participants take the Basel-Berlin Risk Study, a battery of roughly 40 psychological tests, that is considered one of the most thorough measures of the tendency to take risks. In the second, the team evaluated 11,000 respondents’answers to questions on risky behavior from a German population survey. And in the third, they followed Sulloway’s example and sought to classify 200 risk-taking individuals from history — from explorers to revolutionaries to social activists. None of the three avenues of research turned up a link between risk-takers and younger children.

They were forced to conclude, “Our evidence strongly indicates that family dynamics do not produce stable differences in adult risk-taking propensities.”

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Lejarraga’s research is not the only one of its kind. Two independent 2015 studies found no link between birth order and the Big Five traits. One of these, while debunking birth order’s effect on personality, found a credible link between firstborn children and higher intelligence, as measured by IQ tests — a link the authors describe as “minuscule,” however, and as “never mak[ing] a difference in your life.”

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It’s difficult to shake the belief that the order in which we’re born shapes us in some essential, universal way, if only because some experiences seem so fundamental to humanity that they transcend individual circumstances and allow us to find commonality with total strangers — parenthood, for example, having or not having a sibling(s), committed love, the death of a partner, a parent, or a child.

“I absolutely do not think I’d be the person I am today without my sister,” says Divya Shah, 32, of Mumbai. “The kind of joy, happiness or even pain I feel for my sibling has taught me about true and unconditional love more than any other relationship, more than my partner or parents. It has made me more protective of people — especially because I am an older sister — both in terms of ‘what time is she coming home?’ ‘who is she out with?’ but also protective of her feelings.”

It’s impossible to say how much our observations and stereotypes — of ourselves, of our siblings — are influenced by Adler’s work, percolating within cultural consciousness now for more than 100 years, and how much we’ve arrived at them on our own. It’s reflective, perhaps, of the impossibility of proving the effect of birth order on life at all. Even if there is something universal in our experience of being nurtured relative to the order in which we’re born, how much does it even matter? Because drill down one level deeper, and you hit the debate over the effect nature versus nurture has on personality, a conundrum science is even farther from successfully parsing.

“It is quite possible that the position in the sibling sequence shapes the personality — but not in every family in the same way,” Frank Spinath, a psychologist at Saarland University in Germany, told Scientific American. “In other words, there may be an influence — but not a systematic one.”