Why? Even in a completely tolerant world, homosexuality is going to lead to at least modestly inferior life outcomes (smaller dating pool, harder to enjoy the rewards of parenthood, etc). If a person is by nature going to suffer those hardships, certainly we shouldn't add to it with bigotry and probably we should try to help them in at least some ways, but why is it *good*?
There are people who believe that it is *good* that some people are congenitally deaf. And, as we've seen here a couple of times, people who think that it is *good* that some people suffer various mental illnesses. Do you share that view, in the name of tolerance or diversity or whatever?
A young, unmarried mother might have different genes to pass to the child. The more experience a child has at running the family, when the parents are younger and less experienced with more energy to try to be good parents.
"You may be able to think of others besides these."
Maybe older siblings compete with younger siblings in various ways, and, *being older*, naturally win. e.g. maybe older siblings are much more successful at bullying younger siblings than vice-versa.
But they don't always win. They're better at structured reward activities but more maladjusted to social situations seeped in ambiguity - essentially, dealing with peers of various proclivities vs manipulating/pleasung their parents
That doesn't square well with the "path finder" theory. Older siblings have to fight all the fights with the parents, whereas the younger siblings generally profit from the results without having to put in as much of a fight on their own.
I was specifically critical of the "bossing the parents around" statement. Due to the "path finder" aspect of the oldest sibling, I'd argue that younger siblings get to boss around the parents much more often than older siblings.
I agree with your idea though that having to assert yourself on those arguments might provide good practice for later life.
I could have been more clear in my first post though.
Seems like it. Anecdotally (I don't even remember if I participated in the survey) this lines up perfectly with how I would describe myself and my sibling.
This jives with my experience as the youngest sib from 3 boys. Although as a counter, my current age is 29, older sibs are 34 and 35 and I'm the only ACX reader of them :-S
For sure! Having watched a 3 and a 5 year old interact for 3 years, it seems like being a younger sibling means spending a LOT more time being bossed around by someone 2 years older than you. Like, multiple hours per day minimum 😬
Oddly, with my kids it is the opposite. The oldest girl got pushed around by the middle girl, now the youngest pushes around the middle. They are all girls so there isn't boy levels of pushing around, but generally when there is "not playing nicely" behavior it is the younger pulling dominance.
Are children with experience being a bully, or experience effortlessly prevailing in competitions, more likely to go into a STEM career? That would be counterintuitive.
One (trollish) explanation: people who read ACX are Weird. Most people are bullied/pressured out of being Weird by peers or older siblings, with siblings having a stronger influence. Most 1st borns are Normal, and quash ~all incipient Weirdness in younger siblings. But even if the 1st born is Weird, there's still pressure from peers for the younger siblings to be Normal.
Funny, I was just making the argument to someone else that as an only child, I was basically a firstborn whose weirdness could rage unchecked indefinitely.
I'd guess it's more about younger siblings being more influenced by their older sibling than by their parents. which would probably lead to some advantages and some disadvantages.
Oh, interesting. My own default assumption is actually the opposite of Scott’s (1): being older doesn’t matter for the time during which you have your parents’ undivided attention, but rather for the time afterwards when you have significantly *less* attention because your parents are dealing with a newborn, leading you to develop independence and self-direction much younger.
It would be really interesting to look at families where the oldest child had a significant condition or disability that required lots of parental time and attention, to see what effect that had on the younger sibling(s).
Social first-borns are a third parent to their younger siblings. First-borns are replaced as the cutest thing in the household. This is the effect; not more parental attention. They become parent-like and get attention for being helpful instead of cute.
Yes, one of the flaws in the notion of "shared environment effects small -> parenting doesn't matter" is that parents just straight up teach their children differently, not just differentiate in quantity of attention.
Yes, exactly. This is what I wrote above. The older child becomes the leader, hence looks out on the horizon. The younger follows and competes with the older, whilst the older is following the parents.
Yes, exactly. I see I am at least the third to suggest this effect; I should have read further down so as not to duplicate. Insightful folks, ACX readers :-)
As as oldest child, my experience was something like I didn’t fully register the “child” category before my sister was born. When she came along it became clear that we were not 3 equals (my illusion before). It was not a demotion into less attention so much as it was a demotion into a different category of being. They had allowed me to believe I was one of them; when the sibling came along that was suddenly obviously not true. Never to return again, except in echoes if the sibling were sleeping over at a friend’s, out of the house.
Also if Harris’ “nurture assumption” book is correct and peers play a larger role in development than parents do, the older sibling would be an in-home influential peer for the younger in a way that wouldn’t be reciprocal (usually) unless the younger sibling were dramatically more competent in some way.
I think I intervened between my sister and my parents, in terms of trying to interpret their behavior for her. I was never intentionally the “boss” figure partly because one parent worked almost all the time (dad) and so the center of gravity of the household was not usually present, so not easily challenged.
I’ve definitely known people who had to babysit/quasi-raise their younger siblings and that was not my situation.
This is the opposite of my experience. My closest sibling is six years younger than me, and yet I distinctly recall, even prior to their birth, that I didn't at all think of my parents as equals, or even the same as me. I remember being astonished when I learned that they were once children.
We are assuming the parents are the bosses but I often see the first child being the boss of the parents. Then it's easy to be the boss of any younger children.
I'm understanding that birth order effects are strong for a few years, before dropping off around seven years. Some effects seem stronger after a few years, rather than the minimum difference.
Even with that, a full year of difference (pretty much the minimum biologically), can be pretty dramatic. The difference between two and one is huge, and that's when a lot of these effects are being built into the siblings. Sure, by the time we're talking 19 and 20, that's a tiny difference, but by then the relationships are pretty solidly complete.
This was my first thought, and it makes sense why the effect would get stronger as children get closer in age. We have almost irish twins and for better or worse, have always leaned on the oldest one to help with the younger one (and then the younger two), possibly in age inappropriate ways. Had there been a bigger age gap, we wouldn't have needed to rely on the older as much.
And I think this goes against his natural proclivities. He's very much innately not a "first born" child, or at least his first born traits developed much later, compared to our friends first children, which implies to me it's learned behavior.
The middle I think was innately a first born (basically driven and didn't care what other people thought) and he has been molded into a more typical middle child, turning into a pleaser, which I feel is probably not ideal, but it is what it is at this point.
I think this blog's viewership is mostly 30-somethings? regardless of which age bucket it is, any given adult age bracket should be evenly older or younger siblings, I believe
I remember that Scott said on average, older siblings were only 1 year older than younger siblings (out of the entire pool, obviously, not within the same household) so that is probably not the explanation.
I had this thought too, back when we were looking at the first round of results. I think the fact that the effect is stronger for siblings closer in age, and weaker for siblings farther apart in age, contradicts this hypothesis. If it were just that older people had done more stuff and therefore had had more time to stumble across interesting blogs, then we would expect the effect to get stronger the larger the age gap grows. (Though age might explain the Nobel laureates or whatever.)
If you are sampling individuals, rather than families, why should first siblings be older on average?
Like, if this blog attracts readers between the ages of (simplified example) 20 and 40, then there will be some 20-year-old first-borns whose younger siblings are too young to be eligible, and also some 40-year-old second-borns whose older siblings are too old to be eligible, and presumably these cancel out?
Well, it also wasn't arbitrary in the sense that keeping the family's assets intact rather than dividing them is important, and in the sense that having a very clear line of succession minimises infighting, and ultimogeniture would be too likely to put a baby on the throne.
But I see your point that maybe first-borns are meaningfully distinct in other relevant ways too
This is why I want to ask if the thing SSC is selecting for isn’t conscientiousness first and foremost, with programming being full of conscientious people precisely because there really are right and wrong answers
When I think of a field that demands concientious people, I think Civil Engineering, not programming. When you can compile and test your program in seconds it removes much of the need to get it right the first time.
> When you can compile and test your program in seconds it removes much of the need to get it right the first time.
Most programmers can't do that. You can test a few things, but when you're working with dozens of other developpers on a platform that has thousands of users, either you're concientious, or you're going to increase the support workload a lot.
You can't build your software and run tests whenever you want? I mean, sure, you're not doing integration tests all the time. But most 'careless' errors are caught in syntax and unit tests anyhow.
My experience is largely in small team application development, so I can't speak to life in Big Tech. But it seems to me that most software is obviously more tolerant of carelessness than, say, bridge design. You can catch your errors far more cheaply.
It seems like you're assuming careless development but conscientious testing, and then labeling it as un-conscientious overall. It strikes me as the opposite, a conscientious person can still rely on tests to catch their mistakes as part of their process.
Writing good unit tests sounds conscientious to me, and writing code with syntax (or other basic) errors (that you know you will catch with the tests) isn't necessarily a lack of conscientiousness. (edited for typo)
I can build the software and run the unit tests, but the integration tests are ran every day, and need a few dozens of VM. Syntax errors and unit tests don't catch the big issues, which are logic issues when many services are interacting.
> But it seems to me that most software is obviously more tolerant of carelessness than, say, bridge design. You can catch your errors far more cheaply.
It's not like software is built as tolerant as bridges, since its more tolerant. Business won't let you spend as much time on "safety" as if you were a civil engineering firm, because that would be time mostly wasted. Also, there's a great series comparing regular and software engineering from the pespective of people that have done both, concluding that our work are more similar than different https://www.hillelwayne.com/post/are-we-really-engineers/.
I see that sentiment that "we aren't civil engineers" all the time, and I don't understand it. Especially since most of the time it comes from people with absolutely no experience in civil engineering. Software is not a bridge. But the same techniques can be applied. It's all engineering in the end.
I'd say less that catching programming errors is cheaper, and more that FAILURE to catch them is cheaper. A software bug that makes it all the way into production tends to cause less harm than a design flaw in a bridge or an elevator. Especially if the software in question is, say, a video game.
If you had to produce complex software with literally zero bugs, I expect that would be _ruinously_ expensive.
We don't hold software to anything like the same standard as bridges. (This is not just a social difference, but actually a legal one--software is allowed to disclaim liability in ways that other products legally can't.)
The English in the early 20th Century were quite smug about how their system of primogeniture created a strong, calm, self-confident ruling class prepared by their upbringing to rule. Even the House of Commons tended to be full of near-aristocrats: e.g., Mr. Winston Churchill had the good fortune to be in the now-dominant House of Commons because he was the oldest son of Lord Randolph Churchill who was the second oldest son of the Duke of Marlborough.
- Firstborn siblings spend more of their early years exposed to and learning language from adults versus other children who are only slightly older.
- Similarly, firstborn siblings are more directly exposed to praise and expectations from their parents and other adults, vs the praise and social validation of another slightly older child. Thus they become more oriented to achievements that will impress adults, such as performance in school.
Linguistic research on children has found that the critical period of language learning goes until age 10-12, so any child would have had a lot of exposure to lots of other children and adults in the relevant time period. It’s possible that there is a slight effect on margin, but it seems a bit doubtful.
+1. As the firstborn of 4 and the father of 3, the most obvious distinction to me is that the firstborns are socialized by adults while the younger kids are socialized by siblings. This aspect is consistent with the declining effect when age gaps are large - much older siblings aren't around to socialize younger ones.
Are you sure that older siblings aren’t just more likely to try and please authority figures by performing thankless tasks like filling out user surveys ?
In theory I should be able to figure this out - I included a question "How close did you come to not filling out this survey" to see if this could be used to analyze response bias. I don't feel like actually looking at it right now though.
I've read about first-born superiority, so if I were a first-born, I might want to participate to find out more about my superiority. But, in a Harvard class the professor asked the students to raise their hand if they were first born. Most of the room raised their hands. It was a philosophy class. As a second child, I see the oldest one wanting control with their parents in supportive roles. They have good verbal skills and know what to say to get what they want.
Edit: This is wrong! See André Röhm's comment and my response.
<wrong>
Most people are first-born children, if average family size is not too high. Suppose for illustration that 30% of all non-childless families have one child, 40% have two children, and 30% have three children. Then by simple arithmetic, 30%+20%+10%=60% of these children are first-born. And Harvard students come predominantly from well-off families with relatively low birth rates (see https://www.statista.com/statistics/241530/birth-rate-by-family-income-in-the-us/).
I stumbled over it for a bit, but I am pretty confident you made a slight error here.
The real answer in your example is "50% of children are first-borns".
(Do the math for example for 10 families, and calculate the number of total children)
What you calculated was equivalent to answering "If I pick a random family and then pick one of their children at random, what is the chance to select a first-born?". This underestimates the effects of large families.
Even then, I believe your point still stands that first-born's can be more likely than expected. However, if this blog has such a strong selection effect, would we expect Harvard to have none?
You are absolutely right! Doing it properly, the proportion of first-born children is equal to the the reciprocal of the average number of children in non-childless families. In my example, that would be 1/2, but I don't know what the average is over real-life families, or families with a child at Harvard.
Maybe being older you get lots of opportunities to explain/teach things to a younger sibling, this makes you more reflective and self aware hence more likely to go into higher education get a PhD etc. The decline starting at 8 years might be because at 18 you move out and stop teaching your younger sibling things while they are still quite young and can be taught a lot of things, i.e, less than 13.
Yep, makes them nerds perpetually jealous of their cooler younger siblings, who learned social skills from slightly older other kids rather than adults
Absolutely, plus the corollary which is that younger siblings often don't have to learn things for themselves through experience or the hard work of reflection and self-awareness, so they end up getting less practice in those areas. Also, older siblings will often just do hard things for their younger siblings out of impatience, rather than let them figure it out themselves.
There is teaching, but as a second born, I see the first born wanting to control and get the money first, for college. The first born's verbal skills may get their parents to expect more from them and pay more for them. Though they might be the leader, good leaders hire
talented people. A good leader just knows how to control people, time and has a goal. Brains they can hire. They respect time as they usually pay an hourly wage.
As a younger sibling with a B.S. and an older sibling with a doctorate, I came here to post that exact hypothesis.
Anecdotally, siblings relatively close in age are often playmates, and children whose parents are academically inclined definitely engage in play with the older teaching (bragging about?) what they just learned in school. For me about 2/3 of what I encountered through grade 6 I already had pre-exposure to via this method.
It's funny how school changes to impress parents. I brought home new math and my parents had no idea what it was. Then when I was an adult I saw little kids bring home new math and I was dumbfounded even though I had been a math major for a while in college. The kids always impress their parents with the new things they are learning. Parents then think their kids are so smart and decide that kids should go to college. How do they do it? My sister learned the Dewey Decimal System for finding a library book and her kids learned to use a google search.
My personal hypothesis is that the greater uncertainty involved in raising a child for the first time leads to higher openness to new experiences. I'd guess this can go down a number of different paths in practice, but that cultures situated outside of the mainstream will be disproportionately firstborn as a result.
I've heard plenty of tales of parents being overprotective with their firstborn and then realising that kids aren't actually that fragile and letting the younger ones be more freeform, so I'm not sure the cause you're positing exists in the first place
Exactly, my experience and the one I see as well. New parents insist on strict regimes for everything, everyone over-thought and amusing to more experienced parents.
Get down the line and "good enough" is, indeed, good enough
Best advice I got when I became a parent was from a mom of 3 boys. She said to ask myself “Would I be doing this if it were my third kid?” Saved me a lot of effort so far.
I speak from experience as a firstborn. I have distinct memories from high school of feeling resentful that it felt like I was the guinea pig. I certainly can't speak for all firstborns, though, and don't really know if my experience was common.
But the first born learned to use verbal skills to get what he wanted even when parents had made tough rules. More obstacles presents more practice time.
I wonder if that has changed as parenting standards have increased with this generation.
My older brother experienced much of what you did. Unfortunately, most of the experimentation was the cw/assumptions my father made based upon what worked for his own upbringing - go to Catholic school, play football, etc.
My brother did, and even at times felt compelled to profess he liked some aspects of it. But he was miserable. A complete first-born nerd, he would go on to make good friends in college, become a brilliant surgeon, and win an award from his med school, one of the best in the country, for his healthcare policy work.
He was the most miserable adolescent you ever met. His bad experiences at the hands of his peefs haunted him literally for decades.
My parents observed and, once my brother was able to begin to process it all and speak up, accepted his assessment. As a result he moved to an excellent, small, academically oriented school (without a football team) for high school.
I got the benefit of that environment from the third grade, and more importantly of their open-mindedness when I also was not what one would term a typical small-town Louisiana kid.
As a result I was just a more relaxed and amiable kid, comfortable in my skin. Part of it was younger child peer interactions (vs older child pleasing parents). But a big part was I trusted my parents to listen to me and do what was best for me in a way my brother did not experience, and was accepted by my classmates at the smaller, more academic school from a young age.
God bless man. It all works out, but it doesn't mean it's not tough at times
Totally. The first kid into teenage years is the one who triggers all the unresolved teenage trauma in the parents. I had to muddle through it with little guidance. When my sister came along a) they were worn out from fighting me and b) there was a path and c) they realized some of their strategies didn’t work & updated to better ones.
That first born having to fight for what he wants, verbally makes him skilled at this. I have heard about first borns resenting parents, anger fuels their desire to show their parents a thing or two. They see their parents are new at this. Take advantage when possible. I've known first borns who waited to get divorced until after the parent died, so he could show his parents he was a success and right.
How do you know that "birth order" is not just a proxy for "age"? Maybe people who spent more formative years prior to smart phones are more receptive to long essays of the sort that you write.
Could simply filter for respondents over ~20; There's no reason a 40-year-old reader can't have older siblings, so the effect of younger siblings being too young to be readers would only show up in the youngest readers of the blog.
I remember that Scott said on average, older siblings were only 1 year older than younger siblings (out of the entire pool, obviously, not within the same household) so that is probably not the explanation.
- First borns are part of the "parental teaching structure" of subsequent kids.
- and also competitors, cooperators and imitators. I have a 9 yo and 6 yo and I can tell you they are both forever different, on questions of basic personality/desires because they have a sibling. There are things they do/love/hate because of how their sibling feels about them.
- is there any value to looking at school situations (such as Montessori) that often mix age groups? A class room of all 2nd graders is going to have different "social sibling" effects than one that's 1st, 2nd, 3rd all together.
- and what about the past, when almost all kids were raised more or less in a group - a swarm of cousins of varying ages? Being the first born in a house that only ever has 2 kids is one thing. Being the first born in a generation of cousins probably has different implications.
- did you ask any questions about pets (insert snark about "substitute kids") in the household?
You say snark, but my partner and I often joke, only semi tongue in cheek, that our baby is almost getting a second child experience because the dog still needs attention/walks/etc.
I mean, you're definitely right! At this point with joint dog-human society, you might be able to detect sibling effects on the dog too from having an older/younger "sibling" human. Not sure how to do the conversion to dog years though. ;)
You're only looking at 1/3 to 1/2 the picture. The interaction between the siblings, especially the role assumptions that go on.
Our children are 18 months apart. Just before our second was born, my wife took our daughter to the toy store so she could have a baby doll of her own, something that looked a lot like a real baby. Mom had the daughter give her baby doll a name (Baby Mike) ... OK ... with the thinking mom would have here baby, and our 18 month old daughter would have her own baby to mimic mom, instead of wanting to hold her baby sister.
Great idea, but wrong. Baby Mike went into the toy box to almost never return. Yes, she wanted to hold her baby sister, and we allowed this with close supervision, the older daughter was only 18 months after all.
But what happened was a total bonding, the younger grew up faster, as the protégé of the older, and the older did revert some especially when it came to diaper training. We had read about, and expected this.
I think there was growth and leadership developed in the older child, far vision thinking if you will ... which is pretty much what this forum is about.
The younger child didn't/ doesn't look to the horizon as much as she follows her older sister still in a lot of ways, they're 29 & 31 now.
And yes, I'm the elder of two, my sister is 16 months younger than I.
Your eldest is the first grandchild. Kids can compete to have the first grandchild for favoritism {my observation}. So your oldest has a large audience. Don't want to disappoint.
Whenever this topic comes up, I wonder how only children (no siblings) stack up against firstborns. What percentage of this blog’s readers are only children?
I’m also curious about how many female readers of this blog are only children vs male readers.
I knew that about ACX, but I’m curious how many of the readers are only children, and whether the 10% female readership includes an outsize number of only kids.
In 1976, 11% of American women over 40 had borne only one child, but by 2015 22% were “one-and-done”. I have a strong feeling that only children are more or less firstborns, so likely to be over represented here. I’m wondering if that might be especially true for the women, since anecdotally it seems like we’re outliers in various subtle ways.
Maybe “reading ACX” is more of a proxy for “feels benevolently toward or perceives deriving benefit from interactions with analytical males.” Seeing the application of “that brain” to issues in the world at large is one of the draws of ACX for me. Some people (even with STEM careers etc) prefer to only deal with applications of “that brain” occasionally, or only at work & never outside, etc. They might have or use “that brain” themselves but need/want different social input.
So the father-child relationship might influence this. Most of the research seems to look at mother-child dynamics.
LOL I resemble that remark. I like hanging out with analytical males so much, I married one.
I'm currently mostly a homemaker, so this community has been a really valuable outlet for intellectual discussion. I enjoy using "that brain", and indeed most of my close friends have either been men, or women in STEM careers. I've often been the odd woman/humanities major in the room.
My parents didn't have much of a science background, but my dad was a very "no BS" kind of person, and my mother was quite intensely emotional, which I think is why I always found comfort and refuge in an objective, rational approach to the world. And being an only child, I kind of got away with being as weird as I wanted for a longer time than someone with (especially younger) siblings might have.
In my experience youngest siblings can instantly identify each other. They have been strongly socially conditioned; they were always the cutest, they were always smaller than their siblings, and parents had relaxed relative to the first kid. They're used to losing arguments and having things not go their way (being younger and smaller, not necessarily more or less on track), unless they work disproportionately hard for it.
Some anecdotes:
1. My parents *returned* the gameboy I was given as a birthday present, but my youngest sibling was allowed to have multiple consoles.
2. Although I'm three years older than my sister and she's three years older than our youngest sibling, we all learned to read within two years; I was late, she was on time, and the youngest felt left out and taught themself to read at the age of two. (Those early digital books that highlighted and spoke the word at the same work wonders!) Now, of the three of us, 1 and 3 are the most avid readers. (But 2 got a neuroscience degree, she didn't get off easy!)
3. My dad taught us all to program at the same time; we all started with the same level of competence and quickly developed our own styles. Of us, 1 and 3 are employed as software engineers now; 2 lost interest. (This was also part of a larger experiment on us; in the early 2000s there was a theory that girls didn't enter programming because they didn't have a cohort, which my dad found to be a testable hypothesis, so he not only taught us but also most of my sister's school class. It did briefly keep their interest as a communal activity, but it's not clear it had any long term effect.)
I (a first-born) have also surrounded myself with disproportionately first-born friends, I find we're on the same wavelength. But I know I'm pretty unusual, both in general and among first-borns, so I'm cautious about extrapolating my own experience in that regard.
I’m an only child and all my closest friends were either first borns or oldest siblings, or had a much older sibling who was out of the house by the time we met. And even weirder, all our moms had us when they were 38 years old. I subconsciously gravitated toward a whole set of only children born to mothers exactly the same age as mine. It was pretty unusual to have your first kid at 38 in the early 80s, and we didn’t realize we had that in common until years later. I still think that’s kind of wild.
An explanation of the birth-order effect diminishing with age gaps, which still makes the primary driver of the effect parental attention, could be that the first couple of years of a child's life are the ones that require the most parental attention. A second child who is two years younger than their older sibling will get less parental attention than a second child who is six years younger, because in the first situations, the parents are having to deal with a toddler.
I think I was in your "several biological siblings, no social siblings" group, because of the large gap between my older sisters and me (fourteen years). I've often thought I got the best of both worlds growing up. In terms of parental attention, it was like being an only child, but my parents were still experienced parents, and knew what they were doing because of my older sisters.
Notice how society has gone from "it doesn't matter if somebody is gay" to "it's good if some people are gay".
Why? Even in a completely tolerant world, homosexuality is going to lead to at least modestly inferior life outcomes (smaller dating pool, harder to enjoy the rewards of parenthood, etc). If a person is by nature going to suffer those hardships, certainly we shouldn't add to it with bigotry and probably we should try to help them in at least some ways, but why is it *good*?
There are people who believe that it is *good* that some people are congenitally deaf. And, as we've seen here a couple of times, people who think that it is *good* that some people suffer various mental illnesses. Do you share that view, in the name of tolerance or diversity or whatever?
"Baseline" is a complicated term, see the section on choline at https://astralcodexten.substack.com/p/obscure-pregnancy-interventions-much for what I consider pretty good evidence that choline supplementation during pregnancy affects child IQ.
there's a lot of choline in breastmilk so that could potentially cover some of that 6 years
A young, unmarried mother might have different genes to pass to the child. The more experience a child has at running the family, when the parents are younger and less experienced with more energy to try to be good parents.
But the firstborn effect is weaker when the age gap is large. I'd expect the opposite if it were maternal age.
"You may be able to think of others besides these."
Maybe older siblings compete with younger siblings in various ways, and, *being older*, naturally win. e.g. maybe older siblings are much more successful at bullying younger siblings than vice-versa.
Yeah always winning maybe builds your confidence and help make you more persistent in education etc. maybe
But they don't always win. They're better at structured reward activities but more maladjusted to social situations seeped in ambiguity - essentially, dealing with peers of various proclivities vs manipulating/pleasung their parents
How about the first child's experience and ability at bossing the parents around?
That doesn't square well with the "path finder" theory. Older siblings have to fight all the fights with the parents, whereas the younger siblings generally profit from the results without having to put in as much of a fight on their own.
Perhaps asserting yourself in those arguments provides good practice for later life in some way?
I was specifically critical of the "bossing the parents around" statement. Due to the "path finder" aspect of the oldest sibling, I'd argue that younger siblings get to boss around the parents much more often than older siblings.
I agree with your idea though that having to assert yourself on those arguments might provide good practice for later life.
I could have been more clear in my first post though.
Isn't being good at structured reward and bad at ambiguous social situations the nominal path to get into STEM (and thereon to get into ACX) ?
Seems like it. Anecdotally (I don't even remember if I participated in the survey) this lines up perfectly with how I would describe myself and my sibling.
The oldest is saddled with responsibility and success from the start. No time for play unless it's to win.
This jives with my experience as the youngest sib from 3 boys. Although as a counter, my current age is 29, older sibs are 34 and 35 and I'm the only ACX reader of them :-S
For sure! Having watched a 3 and a 5 year old interact for 3 years, it seems like being a younger sibling means spending a LOT more time being bossed around by someone 2 years older than you. Like, multiple hours per day minimum 😬
Oddly, with my kids it is the opposite. The oldest girl got pushed around by the middle girl, now the youngest pushes around the middle. They are all girls so there isn't boy levels of pushing around, but generally when there is "not playing nicely" behavior it is the younger pulling dominance.
Are children with experience being a bully, or experience effortlessly prevailing in competitions, more likely to go into a STEM career? That would be counterintuitive.
One (trollish) explanation: people who read ACX are Weird. Most people are bullied/pressured out of being Weird by peers or older siblings, with siblings having a stronger influence. Most 1st borns are Normal, and quash ~all incipient Weirdness in younger siblings. But even if the 1st born is Weird, there's still pressure from peers for the younger siblings to be Normal.
Funny, I was just making the argument to someone else that as an only child, I was basically a firstborn whose weirdness could rage unchecked indefinitely.
I'd guess it's more about younger siblings being more influenced by their older sibling than by their parents. which would probably lead to some advantages and some disadvantages.
Oh, interesting. My own default assumption is actually the opposite of Scott’s (1): being older doesn’t matter for the time during which you have your parents’ undivided attention, but rather for the time afterwards when you have significantly *less* attention because your parents are dealing with a newborn, leading you to develop independence and self-direction much younger.
It would be really interesting to look at families where the oldest child had a significant condition or disability that required lots of parental time and attention, to see what effect that had on the younger sibling(s).
Social first-borns are a third parent to their younger siblings. First-borns are replaced as the cutest thing in the household. This is the effect; not more parental attention. They become parent-like and get attention for being helpful instead of cute.
Yes, one of the flaws in the notion of "shared environment effects small -> parenting doesn't matter" is that parents just straight up teach their children differently, not just differentiate in quantity of attention.
Yes, exactly. This is what I wrote above. The older child becomes the leader, hence looks out on the horizon. The younger follows and competes with the older, whilst the older is following the parents.
Yes, exactly. I see I am at least the third to suggest this effect; I should have read further down so as not to duplicate. Insightful folks, ACX readers :-)
As as oldest child, my experience was something like I didn’t fully register the “child” category before my sister was born. When she came along it became clear that we were not 3 equals (my illusion before). It was not a demotion into less attention so much as it was a demotion into a different category of being. They had allowed me to believe I was one of them; when the sibling came along that was suddenly obviously not true. Never to return again, except in echoes if the sibling were sleeping over at a friend’s, out of the house.
Also if Harris’ “nurture assumption” book is correct and peers play a larger role in development than parents do, the older sibling would be an in-home influential peer for the younger in a way that wouldn’t be reciprocal (usually) unless the younger sibling were dramatically more competent in some way.
As a first born, did you ever find yourself being the boss of the family, not just younger children?
I think I intervened between my sister and my parents, in terms of trying to interpret their behavior for her. I was never intentionally the “boss” figure partly because one parent worked almost all the time (dad) and so the center of gravity of the household was not usually present, so not easily challenged.
I’ve definitely known people who had to babysit/quasi-raise their younger siblings and that was not my situation.
This is the opposite of my experience. My closest sibling is six years younger than me, and yet I distinctly recall, even prior to their birth, that I didn't at all think of my parents as equals, or even the same as me. I remember being astonished when I learned that they were once children.
That was definitely my experience, and that of my kids.
We are assuming the parents are the bosses but I often see the first child being the boss of the parents. Then it's easy to be the boss of any younger children.
This doesn't quite square with the observation that birth-order effects are strongest when age gaps are smallest though.
I'm understanding that birth order effects are strong for a few years, before dropping off around seven years. Some effects seem stronger after a few years, rather than the minimum difference.
Even with that, a full year of difference (pretty much the minimum biologically), can be pretty dramatic. The difference between two and one is huge, and that's when a lot of these effects are being built into the siblings. Sure, by the time we're talking 19 and 20, that's a tiny difference, but by then the relationships are pretty solidly complete.
The closer they are the most they'll interact.
This was my first thought, and it makes sense why the effect would get stronger as children get closer in age. We have almost irish twins and for better or worse, have always leaned on the oldest one to help with the younger one (and then the younger two), possibly in age inappropriate ways. Had there been a bigger age gap, we wouldn't have needed to rely on the older as much.
And I think this goes against his natural proclivities. He's very much innately not a "first born" child, or at least his first born traits developed much later, compared to our friends first children, which implies to me it's learned behavior.
The middle I think was innately a first born (basically driven and didn't care what other people thought) and he has been molded into a more typical middle child, turning into a pleaser, which I feel is probably not ideal, but it is what it is at this point.
It's cool to see that the effect persists in the new data. It seems that we older siblings need to convince our younger siblings to read this blog!
I'm wondering, does the effect remain when you control for age? First siblings will be older on average.
I think this blog's viewership is mostly 30-somethings? regardless of which age bucket it is, any given adult age bracket should be evenly older or younger siblings, I believe
I remember that Scott said on average, older siblings were only 1 year older than younger siblings (out of the entire pool, obviously, not within the same household) so that is probably not the explanation.
I had this thought too, back when we were looking at the first round of results. I think the fact that the effect is stronger for siblings closer in age, and weaker for siblings farther apart in age, contradicts this hypothesis. If it were just that older people had done more stuff and therefore had had more time to stumble across interesting blogs, then we would expect the effect to get stronger the larger the age gap grows. (Though age might explain the Nobel laureates or whatever.)
If you are sampling individuals, rather than families, why should first siblings be older on average?
Like, if this blog attracts readers between the ages of (simplified example) 20 and 40, then there will be some 20-year-old first-borns whose younger siblings are too young to be eligible, and also some 40-year-old second-borns whose older siblings are too old to be eligible, and presumably these cancel out?
The number of only children in the US doubled between 1971 (11%) and 2015 (22%), so there must be correspondingly fewer siblings.
Makes one wonder if primogeniture wasn’t arbitrary.
Well, it also wasn't arbitrary in the sense that keeping the family's assets intact rather than dividing them is important, and in the sense that having a very clear line of succession minimises infighting, and ultimogeniture would be too likely to put a baby on the throne.
But I see your point that maybe first-borns are meaningfully distinct in other relevant ways too
That's a good call. The older child always seems the more responsible child.
This is why I want to ask if the thing SSC is selecting for isn’t conscientiousness first and foremost, with programming being full of conscientious people precisely because there really are right and wrong answers
When I think of a field that demands concientious people, I think Civil Engineering, not programming. When you can compile and test your program in seconds it removes much of the need to get it right the first time.
Programming requires a lot of high level thinking, holding different threads in your head simultaneously.
Yes, but that's intelligence not concienciousness. I'm a software developer and bottom 1% concientiousness. It seems like a good career fit to me.
> When you can compile and test your program in seconds it removes much of the need to get it right the first time.
Most programmers can't do that. You can test a few things, but when you're working with dozens of other developpers on a platform that has thousands of users, either you're concientious, or you're going to increase the support workload a lot.
You can't build your software and run tests whenever you want? I mean, sure, you're not doing integration tests all the time. But most 'careless' errors are caught in syntax and unit tests anyhow.
My experience is largely in small team application development, so I can't speak to life in Big Tech. But it seems to me that most software is obviously more tolerant of carelessness than, say, bridge design. You can catch your errors far more cheaply.
It seems like you're assuming careless development but conscientious testing, and then labeling it as un-conscientious overall. It strikes me as the opposite, a conscientious person can still rely on tests to catch their mistakes as part of their process.
Writing good unit tests sounds conscientious to me, and writing code with syntax (or other basic) errors (that you know you will catch with the tests) isn't necessarily a lack of conscientiousness. (edited for typo)
I can build the software and run the unit tests, but the integration tests are ran every day, and need a few dozens of VM. Syntax errors and unit tests don't catch the big issues, which are logic issues when many services are interacting.
> But it seems to me that most software is obviously more tolerant of carelessness than, say, bridge design. You can catch your errors far more cheaply.
It's not like software is built as tolerant as bridges, since its more tolerant. Business won't let you spend as much time on "safety" as if you were a civil engineering firm, because that would be time mostly wasted. Also, there's a great series comparing regular and software engineering from the pespective of people that have done both, concluding that our work are more similar than different https://www.hillelwayne.com/post/are-we-really-engineers/.
I see that sentiment that "we aren't civil engineers" all the time, and I don't understand it. Especially since most of the time it comes from people with absolutely no experience in civil engineering. Software is not a bridge. But the same techniques can be applied. It's all engineering in the end.
I'd say less that catching programming errors is cheaper, and more that FAILURE to catch them is cheaper. A software bug that makes it all the way into production tends to cause less harm than a design flaw in a bridge or an elevator. Especially if the software in question is, say, a video game.
If you had to produce complex software with literally zero bugs, I expect that would be _ruinously_ expensive.
We don't hold software to anything like the same standard as bridges. (This is not just a social difference, but actually a legal one--software is allowed to disclaim liability in ways that other products legally can't.)
This is a good poll question
I feel like it shouldn't need to be said that Scott's poll of ACX readers does not generalize to medieval Europe.
I mean, what really is the relevant difference between running a manor and reading essays on nootropics?
And yet!
The English in the early 20th Century were quite smug about how their system of primogeniture created a strong, calm, self-confident ruling class prepared by their upbringing to rule. Even the House of Commons tended to be full of near-aristocrats: e.g., Mr. Winston Churchill had the good fortune to be in the now-dominant House of Commons because he was the oldest son of Lord Randolph Churchill who was the second oldest son of the Duke of Marlborough.
Some other nurture explanations I’ve heard:
- Firstborn siblings spend more of their early years exposed to and learning language from adults versus other children who are only slightly older.
- Similarly, firstborn siblings are more directly exposed to praise and expectations from their parents and other adults, vs the praise and social validation of another slightly older child. Thus they become more oriented to achievements that will impress adults, such as performance in school.
My first born, it was all organic food, Montessori, and no screen time.
Her youngest sibling was born holding an iPad eating a Happy Meal.
And do you feel this had any long-term effects?
Solidarity, brother
This matches my experience.
On the other hand, I'm screwing up certain things less the second time around, so surely that counteracts the effect of my greater laziness?
Linguistic research on children has found that the critical period of language learning goes until age 10-12, so any child would have had a lot of exposure to lots of other children and adults in the relevant time period. It’s possible that there is a slight effect on margin, but it seems a bit doubtful.
+1. As the firstborn of 4 and the father of 3, the most obvious distinction to me is that the firstborns are socialized by adults while the younger kids are socialized by siblings. This aspect is consistent with the declining effect when age gaps are large - much older siblings aren't around to socialize younger ones.
Are you sure that older siblings aren’t just more likely to try and please authority figures by performing thankless tasks like filling out user surveys ?
The comment section needs "Likes" for comments like this one. Perfection
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Funny, but also very serious objection to the premise. The selection may well be taking place at the survey stage, not at the readership stage.
In theory I should be able to figure this out - I included a question "How close did you come to not filling out this survey" to see if this could be used to analyze response bias. I don't feel like actually looking at it right now though.
I've read about first-born superiority, so if I were a first-born, I might want to participate to find out more about my superiority. But, in a Harvard class the professor asked the students to raise their hand if they were first born. Most of the room raised their hands. It was a philosophy class. As a second child, I see the oldest one wanting control with their parents in supportive roles. They have good verbal skills and know what to say to get what they want.
Edit: This is wrong! See André Röhm's comment and my response.
<wrong>
Most people are first-born children, if average family size is not too high. Suppose for illustration that 30% of all non-childless families have one child, 40% have two children, and 30% have three children. Then by simple arithmetic, 30%+20%+10%=60% of these children are first-born. And Harvard students come predominantly from well-off families with relatively low birth rates (see https://www.statista.com/statistics/241530/birth-rate-by-family-income-in-the-us/).
</wrong>
I stumbled over it for a bit, but I am pretty confident you made a slight error here.
The real answer in your example is "50% of children are first-borns".
(Do the math for example for 10 families, and calculate the number of total children)
What you calculated was equivalent to answering "If I pick a random family and then pick one of their children at random, what is the chance to select a first-born?". This underestimates the effects of large families.
Even then, I believe your point still stands that first-born's can be more likely than expected. However, if this blog has such a strong selection effect, would we expect Harvard to have none?
You are absolutely right! Doing it properly, the proportion of first-born children is equal to the the reciprocal of the average number of children in non-childless families. In my example, that would be 1/2, but I don't know what the average is over real-life families, or families with a child at Harvard.
This would be a nightmare to try to control for, but I love it (disclaimer: third child, issues with authority, may be biased)
This is where it might be helpful to have survey data from other blogs that are very different in character from this one.
Maybe being older you get lots of opportunities to explain/teach things to a younger sibling, this makes you more reflective and self aware hence more likely to go into higher education get a PhD etc. The decline starting at 8 years might be because at 18 you move out and stop teaching your younger sibling things while they are still quite young and can be taught a lot of things, i.e, less than 13.
Yep, makes them nerds perpetually jealous of their cooler younger siblings, who learned social skills from slightly older other kids rather than adults
Joke's on my siblings. I stole their toys and made them solve math puzzles to get them back. No social skills were learned in the process.
LOL, that's hilarious and wonderful
Absolutely, plus the corollary which is that younger siblings often don't have to learn things for themselves through experience or the hard work of reflection and self-awareness, so they end up getting less practice in those areas. Also, older siblings will often just do hard things for their younger siblings out of impatience, rather than let them figure it out themselves.
There is teaching, but as a second born, I see the first born wanting to control and get the money first, for college. The first born's verbal skills may get their parents to expect more from them and pay more for them. Though they might be the leader, good leaders hire
talented people. A good leader just knows how to control people, time and has a goal. Brains they can hire. They respect time as they usually pay an hourly wage.
As a younger sibling with a B.S. and an older sibling with a doctorate, I came here to post that exact hypothesis.
Anecdotally, siblings relatively close in age are often playmates, and children whose parents are academically inclined definitely engage in play with the older teaching (bragging about?) what they just learned in school. For me about 2/3 of what I encountered through grade 6 I already had pre-exposure to via this method.
It's funny how school changes to impress parents. I brought home new math and my parents had no idea what it was. Then when I was an adult I saw little kids bring home new math and I was dumbfounded even though I had been a math major for a while in college. The kids always impress their parents with the new things they are learning. Parents then think their kids are so smart and decide that kids should go to college. How do they do it? My sister learned the Dewey Decimal System for finding a library book and her kids learned to use a google search.
There's also far more a 5 year old can teach a 3 year old than an 9 year old can teach a newborn
My personal hypothesis is that the greater uncertainty involved in raising a child for the first time leads to higher openness to new experiences. I'd guess this can go down a number of different paths in practice, but that cultures situated outside of the mainstream will be disproportionately firstborn as a result.
I've heard plenty of tales of parents being overprotective with their firstborn and then realising that kids aren't actually that fragile and letting the younger ones be more freeform, so I'm not sure the cause you're positing exists in the first place
Exactly, my experience and the one I see as well. New parents insist on strict regimes for everything, everyone over-thought and amusing to more experienced parents.
Get down the line and "good enough" is, indeed, good enough
Sure, but that "openness to new experiences" with me (first born) translated into:
-Being one on one homeschooled and raised on the edge of some interesting socially non-conforming groups.
For my little sister, that "good enough" translated to:
-Just go to public school and get fed the standard mainstream culture.
Indeed, classic high variance strategy vs conformity
Best advice I got when I became a parent was from a mom of 3 boys. She said to ask myself “Would I be doing this if it were my third kid?” Saved me a lot of effort so far.
I speak from experience as a firstborn. I have distinct memories from high school of feeling resentful that it felt like I was the guinea pig. I certainly can't speak for all firstborns, though, and don't really know if my experience was common.
I have shades of that as well. I couldn’t believe what my younger sister got away with.
bwahahahahaha, my brother still grouses about it "jokingly"
But the first born learned to use verbal skills to get what he wanted even when parents had made tough rules. More obstacles presents more practice time.
No doubt.
I wonder if that has changed as parenting standards have increased with this generation.
My older brother experienced much of what you did. Unfortunately, most of the experimentation was the cw/assumptions my father made based upon what worked for his own upbringing - go to Catholic school, play football, etc.
My brother did, and even at times felt compelled to profess he liked some aspects of it. But he was miserable. A complete first-born nerd, he would go on to make good friends in college, become a brilliant surgeon, and win an award from his med school, one of the best in the country, for his healthcare policy work.
He was the most miserable adolescent you ever met. His bad experiences at the hands of his peefs haunted him literally for decades.
My parents observed and, once my brother was able to begin to process it all and speak up, accepted his assessment. As a result he moved to an excellent, small, academically oriented school (without a football team) for high school.
I got the benefit of that environment from the third grade, and more importantly of their open-mindedness when I also was not what one would term a typical small-town Louisiana kid.
As a result I was just a more relaxed and amiable kid, comfortable in my skin. Part of it was younger child peer interactions (vs older child pleasing parents). But a big part was I trusted my parents to listen to me and do what was best for me in a way my brother did not experience, and was accepted by my classmates at the smaller, more academic school from a young age.
God bless man. It all works out, but it doesn't mean it's not tough at times
Totally. The first kid into teenage years is the one who triggers all the unresolved teenage trauma in the parents. I had to muddle through it with little guidance. When my sister came along a) they were worn out from fighting me and b) there was a path and c) they realized some of their strategies didn’t work & updated to better ones.
That first born having to fight for what he wants, verbally makes him skilled at this. I have heard about first borns resenting parents, anger fuels their desire to show their parents a thing or two. They see their parents are new at this. Take advantage when possible. I've known first borns who waited to get divorced until after the parent died, so he could show his parents he was a success and right.
How do you know that "birth order" is not just a proxy for "age"? Maybe people who spent more formative years prior to smart phones are more receptive to long essays of the sort that you write.
Could simply filter for respondents over ~20; There's no reason a 40-year-old reader can't have older siblings, so the effect of younger siblings being too young to be readers would only show up in the youngest readers of the blog.
I remember that Scott said on average, older siblings were only 1 year older than younger siblings (out of the entire pool, obviously, not within the same household) so that is probably not the explanation.
Some thoughts:
- Nice work.
- First borns are part of the "parental teaching structure" of subsequent kids.
- and also competitors, cooperators and imitators. I have a 9 yo and 6 yo and I can tell you they are both forever different, on questions of basic personality/desires because they have a sibling. There are things they do/love/hate because of how their sibling feels about them.
- is there any value to looking at school situations (such as Montessori) that often mix age groups? A class room of all 2nd graders is going to have different "social sibling" effects than one that's 1st, 2nd, 3rd all together.
- and what about the past, when almost all kids were raised more or less in a group - a swarm of cousins of varying ages? Being the first born in a house that only ever has 2 kids is one thing. Being the first born in a generation of cousins probably has different implications.
- did you ask any questions about pets (insert snark about "substitute kids") in the household?
You say snark, but my partner and I often joke, only semi tongue in cheek, that our baby is almost getting a second child experience because the dog still needs attention/walks/etc.
I mean, you're definitely right! At this point with joint dog-human society, you might be able to detect sibling effects on the dog too from having an older/younger "sibling" human. Not sure how to do the conversion to dog years though. ;)
I wonder if Kevin Leman reads this blog.
You're only looking at 1/3 to 1/2 the picture. The interaction between the siblings, especially the role assumptions that go on.
Our children are 18 months apart. Just before our second was born, my wife took our daughter to the toy store so she could have a baby doll of her own, something that looked a lot like a real baby. Mom had the daughter give her baby doll a name (Baby Mike) ... OK ... with the thinking mom would have here baby, and our 18 month old daughter would have her own baby to mimic mom, instead of wanting to hold her baby sister.
Great idea, but wrong. Baby Mike went into the toy box to almost never return. Yes, she wanted to hold her baby sister, and we allowed this with close supervision, the older daughter was only 18 months after all.
But what happened was a total bonding, the younger grew up faster, as the protégé of the older, and the older did revert some especially when it came to diaper training. We had read about, and expected this.
I think there was growth and leadership developed in the older child, far vision thinking if you will ... which is pretty much what this forum is about.
The younger child didn't/ doesn't look to the horizon as much as she follows her older sister still in a lot of ways, they're 29 & 31 now.
And yes, I'm the elder of two, my sister is 16 months younger than I.
Your eldest is the first grandchild. Kids can compete to have the first grandchild for favoritism {my observation}. So your oldest has a large audience. Don't want to disappoint.
Whenever this topic comes up, I wonder how only children (no siblings) stack up against firstborns. What percentage of this blog’s readers are only children?
I’m also curious about how many female readers of this blog are only children vs male readers.
Anecdote time: I'm an only child and a female reader of this blog.
Female reader here, one younger sibling (sister), five-year age difference.
But I was born when my dad was a physics PhD student, so this blog or something like it was pretty much looming ahead of me from the get-go.
The response is usually 90:10 male: female split.
I knew that about ACX, but I’m curious how many of the readers are only children, and whether the 10% female readership includes an outsize number of only kids.
In 1976, 11% of American women over 40 had borne only one child, but by 2015 22% were “one-and-done”. I have a strong feeling that only children are more or less firstborns, so likely to be over represented here. I’m wondering if that might be especially true for the women, since anecdotally it seems like we’re outliers in various subtle ways.
Maybe “reading ACX” is more of a proxy for “feels benevolently toward or perceives deriving benefit from interactions with analytical males.” Seeing the application of “that brain” to issues in the world at large is one of the draws of ACX for me. Some people (even with STEM careers etc) prefer to only deal with applications of “that brain” occasionally, or only at work & never outside, etc. They might have or use “that brain” themselves but need/want different social input.
So the father-child relationship might influence this. Most of the research seems to look at mother-child dynamics.
LOL I resemble that remark. I like hanging out with analytical males so much, I married one.
I'm currently mostly a homemaker, so this community has been a really valuable outlet for intellectual discussion. I enjoy using "that brain", and indeed most of my close friends have either been men, or women in STEM careers. I've often been the odd woman/humanities major in the room.
My parents didn't have much of a science background, but my dad was a very "no BS" kind of person, and my mother was quite intensely emotional, which I think is why I always found comfort and refuge in an objective, rational approach to the world. And being an only child, I kind of got away with being as weird as I wanted for a longer time than someone with (especially younger) siblings might have.
I saw those graphs and immediately thought of Benford’s Law.
In my experience youngest siblings can instantly identify each other. They have been strongly socially conditioned; they were always the cutest, they were always smaller than their siblings, and parents had relaxed relative to the first kid. They're used to losing arguments and having things not go their way (being younger and smaller, not necessarily more or less on track), unless they work disproportionately hard for it.
Some anecdotes:
1. My parents *returned* the gameboy I was given as a birthday present, but my youngest sibling was allowed to have multiple consoles.
2. Although I'm three years older than my sister and she's three years older than our youngest sibling, we all learned to read within two years; I was late, she was on time, and the youngest felt left out and taught themself to read at the age of two. (Those early digital books that highlighted and spoke the word at the same work wonders!) Now, of the three of us, 1 and 3 are the most avid readers. (But 2 got a neuroscience degree, she didn't get off easy!)
3. My dad taught us all to program at the same time; we all started with the same level of competence and quickly developed our own styles. Of us, 1 and 3 are employed as software engineers now; 2 lost interest. (This was also part of a larger experiment on us; in the early 2000s there was a theory that girls didn't enter programming because they didn't have a cohort, which my dad found to be a testable hypothesis, so he not only taught us but also most of my sister's school class. It did briefly keep their interest as a communal activity, but it's not clear it had any long term effect.)
I (a first-born) have also surrounded myself with disproportionately first-born friends, I find we're on the same wavelength. But I know I'm pretty unusual, both in general and among first-borns, so I'm cautious about extrapolating my own experience in that regard.
I’m an only child and all my closest friends were either first borns or oldest siblings, or had a much older sibling who was out of the house by the time we met. And even weirder, all our moms had us when they were 38 years old. I subconsciously gravitated toward a whole set of only children born to mothers exactly the same age as mine. It was pretty unusual to have your first kid at 38 in the early 80s, and we didn’t realize we had that in common until years later. I still think that’s kind of wild.
An explanation of the birth-order effect diminishing with age gaps, which still makes the primary driver of the effect parental attention, could be that the first couple of years of a child's life are the ones that require the most parental attention. A second child who is two years younger than their older sibling will get less parental attention than a second child who is six years younger, because in the first situations, the parents are having to deal with a toddler.
I think I was in your "several biological siblings, no social siblings" group, because of the large gap between my older sisters and me (fourteen years). I've often thought I got the best of both worlds growing up. In terms of parental attention, it was like being an only child, but my parents were still experienced parents, and knew what they were doing because of my older sisters.
Yeah, speaking as the youngest child, with a 12 year age gap between my youngest sibling me, your explanation seems pretty obviously correct.