An intriguing feature of twin studies: anything a parent does to individualize for a child is non-shared-environment (NSE) rather than shared environment (SE, viz. ”parenting”). The more a parent optimizes for individual agency, the less “parenting” will be attributed.
Claude at least basically confirmed this interpretation (it says it is “slightly overstated” but then gives a “clarification” that doesn’t change it). My reaction was “wait WHAT”—doesn’t that completely invalidate the whole “parenting doesn’t significantly matter for future life outcomes” claim?
Because that claim is based on equating “parenting” with “shared environment”. But if you equate “parenting” with just “what are the ways in which parents treat each child identically” then it seems that of course that will only have a small effect.
I for one know that I interact very differently with children with different personalities! (Or, for that matter, with adults with different personalities.) One classic example of this is that children who are naturally compliant and “easy” are disciplined/punished less, because there’s much less of a need to do so.
I would intuitively expect that the amount of ways in which parents treat each child exactly the same would be very small. As an extreme case, parents who engage in child abuse may sometimes be abusive toward only some of their children, while treating the rest more or less normally; e.g. because some of the children have traits that the parents happen to intensely dislike. Even if we don’t go that far, most parents will get along better with some of their children than others. One child might be more on the same wavelength with mom while their sibling is more on the same wavelength with dad, etc.
How isn’t this talked about more as an enormous caveat to those “parenting doesn’t matter” studies? (ping @Steven Byrnes )
Claude Opus 4 on non-shared environment claim
is this accurate:
“An intriguing feature of twin studies: anything a parent does to individualize for a child is non-shared-environment (NSE) rather than shared environment (SE). and when people claim twin studies show parenting doesn’t matter, they’re conflating parenting with shared-environment when non-shared-environment contains parenting too.”
This is largely accurate, but needs some clarification.
The statement correctly identifies that differential parenting—when parents treat their children differently—gets categorized as non-shared environment (NSE) in twin studies. This is indeed a crucial point that’s often misunderstood.
However, the claim that “anything a parent does to individualize for a child is NSE” is slightly overstated. More precisely:
Shared environment (SE) includes parenting behaviors that affect all children in a family similarly—like general parenting style, family rules, socioeconomic status, neighborhood, etc.
Non-shared environment (NSE) includes parenting behaviors that differ between children—like favoritism, different responses to each child’s temperament, birth order effects, or tailoring approaches to each child’s needs.
The second part is spot-on: when people claim “twin studies show parenting doesn’t matter,” they’re often making the error of equating all parenting with shared environment. Since shared environment typically shows small effects in many twin studies (especially for personality traits and IQ in adults), they conclude parenting is unimportant. But this ignores that differential parenting is captured in the non-shared environment component, which often shows substantial effects.
This is a sophisticated critique of how twin study results are commonly misinterpreted. The reality is that parenting can matter enormously—it’s just that the ways parents adapt to and treat each child individually may matter more than their general parenting approach that applies to all children equally.
Claude Opus 4 on factors causing differential parenting
Parents naturally:
Respond to each child’s temperament differently
Adjust discipline strategies based on what works for each child
Have different relationship qualities with different children
Spend different amounts of time with each child based on needs/interests
Express affection differently based on each child’s preferences
Set different expectations based on each child’s abilities
Child characteristics:
Age/developmental stage—Parents adapt their approach as each child grows, so siblings experience different parenting at the same chronological age
Gender—Despite intentions, parents often interact differently with boys vs. girls
Physical appearance—Children who resemble a favored (or disfavored) relative may be treated differently
Health/disabilities—A child with chronic illness, ADHD, learning disabilities, etc. often receives different parenting
Birth order—Firstborns often get more anxious/intensive parenting; later children more relaxed parenting
Temperament match—An extroverted parent might click better with their outgoing child than their introverted one
Situational factors:
Parental life circumstances—Parents going through divorce, job loss, depression, etc. during one child’s formative years but not another’s
Family composition changes—Only children who later get siblings experience very different early years
Economic changes—One child might grow up during prosperity, another during financial hardship
Parental learning—Parents often say they were “different parents” to their younger children after learning from mistakes
Relationship dynamics:
Goodness of fit—Some parent-child pairs just “click” better due to shared interests, communication styles, humor
Behavioral cycles—A difficult child may elicit harsher parenting, which increases difficulty, creating a feedback loop
Triangulation—In some families, one child becomes the “peacemaker” or “scapegoat,” receiving distinct treatment
Identification—Parents may see themselves in one child more than another, leading to different expectations/treatment
Unintentional differences:
Parental energy/age—A 25-year-old parent has different energy than a 40-year-old parent
Comparison effects—Parents may push a child harder (or less) based on their siblings’ achievements
Time availability—Work schedules, other children’s needs, etc. affect how much one-on-one time each child gets
All of these create non-shared environment effects in twin studies, yet they’re clearly parenting factors that could significantly impact outcomes.
Like I always say, the context in which you’re bringing up heritability matters. It seems that the context here is something like:
Some people say shared environment effects are ≈0 in twin & adoption studies, therefore we should believe “the bio-determinist child-rearing rule-of-thumb”. But in fact, parenting often involves treating different kids differently, so ‘shared environment effects are ≈0’ is irrelevant, and therefore we should reject “the bio-determinist child-rearing rule-of-thumb” after all.
If that’s the context, then I basically disagree. Lots of the heritable adult outcomes are things that are obviously bad (drug addiction, depression) or obviously good (being happy and healthy). Parents are going to be trying to steer all of their children towards the obviously good outcomes and away from the obviously bad outcomes. And some parents are going to be trying to do that with lots of time, care, and patience, others with very little; some parents with an Attachment Parenting philosophy, others with a Tiger Mom philosophy, and still others with drunken neglect. If a parent is better-than-average at increasing the odds that one of their children has the good outcomes and avoids the bad outcomes, then common sense would suggest that this same parent can do the same for their other children too, at least better than chance. That doesn’t require an assumption that the parents are doing the exact same things for all their children. It’s just saying that a parent who can respond well to the needs of one kid would probably (i.e. more-than-chance) respond well to the needs of another kid, whatever they are, whereas the (e.g. drunk and negligent) parents who are poor at responding to the needs of one kid are probably (i.e. more-than-chance) worse-than-average at responding to the needs of another kid.
And yet, the twin and adoption studies show that shared environmental effects are ≈0 for obviously good and obviously bad adult outcomes, just like pretty much every other kind of adult outcome.
In other words, nobody is questioning that a parent can be abusive towards one child but not another. Rather, it would be awfully strange if a parent who was abusive towards one child was abusive towards another child at exactly the population average rate. There’s gonna be a correlation! And we learn something important from the fact that this correlation in child-rearing has immeasurably small impact on adult outcomes.
Likewise, adoptive siblings may have different screen time limitations, parents attending or not attending their football games, eating organic versus non-organic food, parents flying off the handle at them, being in a better or worse school district, etc. But they sure are gonna be substantially correlated, right?
Like I always say, the context in which you’re bringing up heritability matters.
My context is most strongly the one where I’m trying to reconcile the claims from therapy vs. heredity. I know we did already agree on one particular mechanism by which they could be reconciled, but just that by itself doesn’t feel like it would explain some of the therapy claims where very specific things seem to be passed on from parents.
But yeah, I think that does roughly correspond to arguing over whether the bio-determinist child-rearing rule of thumb applies or not.
And yet, the twin and adoption studies show that shared environmental effects are ≈0 for obviously good and obviously bad adult outcomes, just like pretty much every other kind of adult outcome.
In other words, nobody is questioning that a parent can be abusive towards one child but not another. Rather, it would be awfully strange if a parent who was abusive towards one child was abusive towards another child at exactly the population average rate. There’s gonna be a correlation!
On one hand, this does make sense. On the other hand—as far as I know, even the researchers who argue for the strongest bio-determinist case will make the caveat that of course none of this applies to cases of sufficiently extreme abuse, which will obviously mess someone up.
But… if that is in fact the case, shouldn’t it by your argument show up as a shared environment effect?
I can think of a few different explanations:
Even extreme childhood abuse doesn’t have a major effect on life outcomes.
(Including this one for completeness though I consider it obviously implausible.)
The level of abuse that would affect life outcomes is rare enough not to be picked up on in the studies.
The methodology of the studies creates on floor on the badness of outcomes that gets picked up; e.g. maybe adoptive parents are screened well enough to make the worst abuse not happen, and the people drawn from national twin registers and contacted to fill in surveys don’t bother responding if their lives are so messed up they don’t have the time or energy for that.
But at least studies that use national registers about e.g. incarceration should be able to control for this.
There’s something wrong about the correlation argument.
When I asked Claude about this, it claimed that actually, studies done with national registers find a significant shared environment effect on antisocial behavior and criminality. It gave me this cite which reports a 26% shared environment effect on antisocial behavior defined as various forms of crime (property offenses, violent offenses, and drug-related offenses), measured from childhood to early adulthood [20 years], and also cited some previous work with similar findings.
I wasn’t sure whether that study was at all representative or cherry-picked so I looked at studies citing it and found this paper on antisocial behavior specifically, which has this mention:
After quantifying the relative importance of environmental effects overall (without specifying what they are), a natural next step is to examine what specific environmental exposures might contribute to variation in ASB within a genetically informed framework. One putative environmental exposure of interest is negative parenting, which may encompass harsh and inconsistent parental discipline as well as negative parental feeling towards one’s children (Burt 2022, Burt et al. 2021, Jaffee et al. 2012). Some genetically informed studies have shown that negative parenting can act as a genuinely environmental causal risk factor for child ASB (Burt et al. 2021, Caspi et al. 2004, Dotterer et al. 2023, Klahr et al. 2017, Larsson et al. 2008b, Waller et al. 2018). For example, Waller and colleagues (2018) employed a monozygotic twin difference design to investigate whether identical twins, who share all of their genetic makeup and shared environment but are exposed to different levels of parental harshness and warmth, differ in their levels of callous-unemotional traits and aggression. Their results indicated that the twin who experienced more negative parenting displayed higher levels of ASB, consistent with an environmental effect of parenting on child ASB over and above the genetic effects (Waller et al. 2018).
Which sounds like even identical twins may be treated differently enough by the same parents for it to have noticeable effects?
Will Eden’s blog post that Buck linked to below mentions that
For example, parental warmth and control have been assessed in hundreds of studies as the two ‘super-factors’ of parenting which are then correlated with children’s outcomes. These studies have traditionally assumed that parenting is a shared environmental factor in the sense that only one child per family was considered and parent–child associations were analyzed ‘between’ families. However, by studying more than one child per family and by targeting parenting that is specific to each child, it is possible to investigate the extent to which parents’ warmth and control differ for children ‘within’ families. Research of this kind has shown that parents do treat their children differently. If you ask parents about their differential parenting they report only modest differential parenting (sibling correlations of ~0.70) but if you ask children about it you might think they were raised in different families (sibling correlations of ~0.25). Observations of parent–child interactions support not the parents’ but the children’s view (sibling correlations of ~0.20).
In short, parents think they treat their kids the same… but the kids think the parents treat them differently, and outside observations would support this claim. If anything, the outside observer sees slightly more unequal treatment than the kids themselves do. This indicates that the vast majority of parenting effects would show up in the non-shared environment.
So given all of that, when you say
If a parent is better-than-average at increasing the odds that one of their children has the good outcomes and avoids the bad outcomes, then common sense would suggest that this same parent can do the same for their other children too, at least better than chance.
Then maybe this is wrong, at least when we restrict the range of parenting to not-obviously-horribly-abusive which doesn’t seem to get clearly picked up for whatever reason. I agree that it’s certainly weird and counterintuitive that it’s wrong, but I’m not sure that explaining it by “maybe parents just have a minimal effect overall” makes things any less weird and counterintuitive!
Conditional on there only being a small-ish shared environment effect, “even parents who try their best may easily screw up and be unable to overcome their own emotional issues enough to provide consistent parenting to all of their kids” doesn’t sound less implausible to me than “parenting just has no effect”.
It’s easy for me to imagine that e.g. a parent who pushes their children to socialize may benefit some of their children in the long-term while overwhelming their more introvert or socially anxious kids; that a parent that leans neurotypical vs. autistic could have an intuitive understanding of their kids who are like them but end up not parenting the unlike-them kids well; that a parent would relate significantly differently to their girls than their boys; and so on.
Also I suspect that reducing things to a single spectrum of “does one’s parenting have good or bad effects” is too simplistic. For instance, Eliezer has a post where he mentions that:
Of the people I know who are reaching upward as rationalists, who volunteer information about their childhoods, there is a surprising tendency to hear things like: “My family joined a cult and I had to break out,” or “One of my parents was clinically insane and I had to learn to filter out reality from their madness.”
My own experience with growing up in an Orthodox Jewish family seems tame by comparison… but it accomplished the same outcome: It broke my core emotional trust in the sanity of the people around me.
Until this core emotional trust is broken, you don’t start growing as a rationalist. I have trouble putting into words why this is so. Maybe any unusual skills you acquire—anything that makes you unusually rational—requires you to zig when other people zag. Maybe that’s just too scary, if the world still seems like a sane place unto you.
Now I think that this is too strong—you can probably become a rationalist even without that kind of a background—but if we accept that this was the origin story for some rationalists, then… growing up in a cult or having a clinically insane parent, so that your “core emotional trust in the sanity of the people around you” is broken, certainly sounds like it should have an overall “bad effect”. And probably it does have some bad effects. But on the other hand, if it also makes you into an upstanding critical thinker, that probably contributes to good outcomes? Which of those effects dominates? Idk, probably depends a lot on your environment and how lucky you get and it could go either way.
In therapy there’s also the finding that different people may respond to exactly the same issue with the opposite emotional strategies, so if two children grew up in a cult, maybe one of them would lose all capability for critical thinking and the other would become a super-rationalist. This could be partially driven by genetic factors, but then if their parents didn’t join a cult, those same genetics would probably lead to more moderate outcomes.
So rather than going with the bio-determinist rule of thumb that “things you do as a parent will have generally small or zero effects on what the kid will be like as an adult”, maybe it’s more like “things you do as a parent will have generally small or zero predictable effects on what the kid will be like as an adult”—if your kids had gotten a different set of parents, they might get significantly different outcomes, but there’s no clear way of predicting how those outcomes are different. With you as their parent, your son gets outcomes [good A, bad B, neutral C] and your daughter gets [good A, neutral B, bad C]; with some other parent, your son would get [neutral A, bad B, good C] and your daughter would get [good A, bad B, neutral C].
Even extreme childhood abuse doesn’t have a major effect on life outcomes.
(Including this one for completeness though I consider it obviously implausible.)
The level of abuse that would affect life outcomes is rare enough not to be picked up on in the studies.
The methodology of the studies creates on floor on the badness of outcomes that gets picked up; e.g. maybe adoptive parents are screened well enough to make the worst abuse not happen, and the people drawn from national twin registers and contacted to fill in surveys don’t bother responding if their lives are so messed up they don’t have the time or energy for that.
But at least studies that use national registers about e.g. incarceration should be able to control for this.
There’s something wrong about the correlation argument.
I vote for the second one—the result is usually “shared environment effects on adult outcomes are statistically indistinguishable from zero” but that doesn’t mean they’re exactly 0.00000…. :)
It gave me this cite which reports a 26% shared environment effect on antisocial behavior defined as various forms of crime (property offenses, violent offenses, and drug-related offenses), measured from childhood to early adulthood [20 years], and also cited some previous work with similar findings.
There are definitely huge shared environment effects during the period where kids are living with their parents. No question about it!
(Also, for the record, some measurements seem to be adult outcomes, but are also partly measuring stuff that happened when kids were living with their parents—e.g. “having ever attended college”, “having ever been depressed”, “having ever gotten arrested”, etc. Those tend to have big shared environment effects too.)
[Waller et al. 2018] sounds like even identical twins may be treated differently enough by the same parents for it to have noticeable effects?
The result there is “parents are harsher and less warm towards their kids who are more callous and aggressive”, and when you phrase it that way, it seems to me that the obvious explanation is that parents behave in a way that is responsive to a kid’s personality.
Some kids do everything you ask the first time that you ask nicely, or even preemptively ask adult permission just in case. Other kids are gleefully defiant and limit-testing all the time. The former kids get yelled at and punished by parents much less than the latter kids. (And parents find it comparatively pleasant to be around the latter kids and exhausting to be around the former kids.) This all seems very obvious to me, right?
Thus, if per Will Eden “parents think they treat their kids the same… but the kids think the parents treat them differently, and outside observations would support this claim”, I’d guess that the parent would say something like: “the household rule is: I’ll watch TV at night with any child who wants to do that and who sits quietly during the show, and another household rule is: if you jump on the couch then you have to go to your room, etc. I apply these rules consistently to all my children”. And the parent is correct—they are in fact pretty consistent in applying those rules. But meanwhile, the kids and outside observers just notice that one sibling winds up getting punished all the time and never joining in the evening TV, while the other sibling is never punished and always welcome for TV.
In my post I poked fun at a study in the same genre as Waller et al. 2018. I wrote: “I propose that the authors of that paper should be banned from further research until they have had two or more children.” Of course, for all I know, they have lots of kids, and they have babysat and hung out with diverse classes of preschoolers and kids (as I have), and yet they still subscribe to this way of thinking. I find it baffling how people can look at the same world and interpret it so differently. ¯\_(ツ)_/¯
Anyway, that other study didn’t even mention the (IMO primary and obvious) causal pathway from child personality to parental treatment at all, IIRC. The Waller et al. 2018 study does a bit better: it mentions something like that pathway, albeit with an unnecessarily-exotic description: “Evocative rGE reflects situations in which the child elicits an environment consonant with his/her genes (e.g., a callous child frequently rejects parental warmth, causing his/her parents to eventually reduce their levels of warmth).”), and they claim that their study design controls for it. What they mean is actually that they (imperfectly) controlled for the “child genes → child personality → parental treatment” pathway (because the children are identical twins). But they don’t control for the “random fluctuations in such-and-such molecular signaling pathway during brain development or whatever → child personality → parental treatment” pathway. I find that pathway much more plausible than their implied preferred causal pathway of (I guess) “parents are systematically warmer towards one twin than another, just randomly, for absolutely no upstream reason at all → child personality”. Right?
I think the only way to see parental effects without getting tripped up by the child personality → parental treatment pathway is to rely on the fact that some parents are much more patient or harsh than others, which (my common sense says) is a huge source of variation. Just look around and see how differently different parents, different babysitters, different teachers interact with the very same child. That brings us to adoption studies, which find that parenting effects on adult outcomes are indistinguishable from zero. So I’m inclined to trust that finding over the studies like Waller et al. 2018.
By the way, Will Eden cites Plomin, but meanwhile Turkheimer reviews many of the same studies and says the results are basically zero (he calls this “the gloomy prospect”). (Turkheimer is Plomin’s reference 41.) It would be interesting to read them side-by-side and figure out why they disagree and who to believe—I haven’t done that myself.
I’m not sure that explaining it by “maybe parents just have a minimal effect overall” makes things any less weird and counterintuitive!
I don’t find these things counterintuitive, but rather obvious common sense. I can talk a bit about where I’m coming from.
There are many things that I did as a kid, and when I was an adult I found that I didn’t enjoy doing them or find it satisfying, so I stopped doing them. Likewise, I’ve “tried on” a lot of personalities and behaviors in my life as an independent adult—I can think of times and relationships in which I tried out being kind, mean, shy, outgoing, frank, dishonest, impulsive, cautious, you name it. The ways-of-being that felt good and right, I kept doing, the ones that felt bad and wrong, I stopped. This is the picture I suggested in Heritability, Behaviorism, and Within-Lifetime RL, and feels very intuitive to me.
Also, my personality and values are very very different from either my parents’ personalities, or the personality that my parents would have wanted to instill in me.
I guess the childhood trauma thing is important to your intuitions, which we were chatting about in the comments of my post. I can share my first-person perspective on that too: I was blessed with a childhood free of any abuse or trauma. But I’m kinda neurotic, and consequently have wound up with very very dumb memories that feel rather traumatic to me and painful to think about. There is absolutely no good reason for these memories to feel that way—I’m thinking of perfectly fine and normal teenage things that I have no objective reason to be embarrassed about, things in the same ballpark as “my parents walked on me masturbating, and promptly apologized for not knocking and politely left, and never brought it up again”. (My actual painful memories are even dumber than that!) Just as you were speculating in that comment thread, I think I’m predisposed to dwell on certain types of negative memories (I’m very big into embarrassment and guilt), and in the absence of any actual objectively terrible memories to grab onto, my brain has grabbed onto stupid random teenager stuff.
I am able to take the harsh edge off these memories by CBT-type techniques, although I haven’t really bothered to do that much because I’m lazy and busy and AFAICT those memories are not affecting my current behavior too much. (I’m somewhat introverted in part from being oversensitive to social embarrassment and guilt, but it’s not that bad, and my uninformed guess is that finding peace with my dumb teenage memories wouldn’t help much.)
things you do as a parent will have generally small or zero predictable effects on what the kid will be like as an adult
Is there any action-relevant difference between “no effect” and “no predictable effect”?
Hmm, I think it might be good to sharpen the context a bit more, as I feel we might be slightly talking past each other.
The argument that I’m the most focused on questioning is, to be clear, one that you haven’t made and which isn’t in your writings on this topic. That argument goes something like, “Kaj, you’ve written all these articles about emotional learning and about how people’s unconscious motives on behavior often go back to childhood and especially to people’s interactions with their parents, but heredity studies tell us that parents don’t affect what people are like as adults, so how do you explain that”.
And it gets a bit subtle since there are actually several different versions of that question:
“Therapy books sometimes give the impression that everything about a person’s life is determined based on their childhood circumstances. How do you justify that, given twin studies?”—Very fair question! Some therapy books do give that impression, and such a claim is clearly incorrect. I’m not going to defend that claim. I think it’s basically a result of selection bias. The people who got lucky enough with their genes that they make it through sucky childhoods without major issues don’t see therapists, and then therapists write books that draw on their clinical experience based on clients that have been selected for having unlucky genes.
“Okay, but even if not everything about a person’s issues is determined by their childhood circumstances, the therapy books still say that stuff like parental warmth is a major factor on a person’s future psychology. But wouldn’t that imply a bigger shared environment effect?”—Also a very fair question, and the thing that I’m the most interested in figuring out/explaining! And I’m trying to explain that with something like “maybe parents have counterintuitively different effects on different children, and also the specific psychological issues this may cause don’t necessarily map linearly to the kinds of outcome variables the studies are looking at”.
“So from twin studies, we know that parents have basically no causal effect whatsoever on the children, so...”—Okay now my imagined interlocutor is going too far, the twin studies don’t say that. Parents still have some causal effects on their children—such as the children having memories of being raised by their parents, that would be different if they’d had different parents! But, I’ve talked with some people who did seem to take their interpretation of the studies that far! So I’d like to at least establish an argument that makes it clear why that is wrong.
And as an aside, when I say “therapy books”, I also mean my own personal experience with coaching people and applying the kinds of techniques the therapy books talk about. Quite often childhood stuff or stuff about parents pops up, even when the questions I ask don’t reference childhood in any way.
So when you say that
I don’t find these things counterintuitive, but rather obvious common sense. I can talk a bit about where I’m coming from.
There are many things that I did as a kid, and when I was an adult I found that I didn’t enjoy doing them or find it satisfying, so I stopped doing them. Likewise, I’ve “tried on” a lot of personalities and behaviors in my life as an independent adult—I can think of times and relationships in which I tried out being kind, mean, shy, outgoing, frank, dishonest, impulsive, cautious, you name it. The ways-of-being that felt good and right, I kept doing, the ones that felt bad and wrong, I stopped. This is the picture I suggested in Heritability, Behaviorism, and Within-Lifetime RL, and feels very intuitive to me.
Also, my personality and values are very very different from either my parents’ personalities, or the personality that my parents would have wanted to instill in me.
Then, on the one hand, I do agree with your reasoning here, and what you say also agrees with my own experience of what I’m like as an adult vs. what my parents are like.
On the other hand, when talking about the study of adolescent/young adult antisociality, you mention that parents do have a significant effect on their children when the children are still living with them. And it’d be pretty weird if the degree of adolescent/young adult antisociality had no effect on what one is like as an adult. That’s especially so since the measure of antisociality in this study was, basically, “has the person committed property crimes, violent crimes, or drug-related crimes”.
From the perspective of questions #2 and #3, I might say: “Whether you commit crimes as an adolescent has to have some predictive effect on your future outcomes. Obviously it’s not a deterministic effect—even if you deal drugs as a teenager and beat someone up for not paying their drug debt to you, it’s still totally possible to put all of that behind you and end up as a well-adjusted adult. But you would expect such a person to be statistically less likely to end up with good outcomes than someone who committed zero crimes in their teens, right?”
“So I’m honestly a little confused how to reconcile ‘significant shared environment effect on crime when an adolescent’ with ‘basically no shared environment effect on adult outcomes’. But maybe it’s just the case that serious crime as youth is pretty rare in the first place, and not getting over it is more rare still! (Especially given that the study covered people who grew up in Sweden ca. 1985-2006.) Still, I would expect that the people who used to commit crime as teenagers will have a different psychological profile than the people who never did, even if their background ends up ultimately not affecting the coarse kinds of variables that the other twin studies measure. For instance, maybe they feel shame and guilt about what they’ve done and will want to process that with a therapist later, or maybe they have some anxiety of their past catching up on them… even if neither of those is the kind of thing that’d be picked up on the twin studies. So I feel like that should answer the skeptical voice asking questions #2 and #3.”
To take another example—when I was a kid, I wore shoes with no laces on them and somehow nobody taught me to tie my shoelaces until I got to a point where it was embarrassing not to know how to do it. As a defensive move, I made it into an identity thing that “I’m not the kind of person who uses shoes with laces”. I continued with that way all the way until I was about to turn 30, at which point I finally acknowledged that I was being stupid, looked up some YouTube video titled “the easiest way to teach your kid to tie their shoelaces”, and taught myself to tie shoelaces.
I’m pretty sure there was a causal connection between that sequence of events and me having the parents that I had, since some other parents would just have taught me to tie my shoelaces earlier. And it had a slight negative effect on my self-esteem during that time. But again neither of those was the kind of a thing that would be picked up on twin studies. (Especially since I don’t have a twin, but never mind that.)
Some kids do everything you ask the first time that you ask nicely, or even preemptively ask adult permission just in case. Other kids are gleefully defiant and limit-testing all the time. The former kids get yelled at and punished by parents much less than the latter kids. (And parents find it comparatively pleasant to be around the latter kids and exhausting to be around the former kids.) This all seems very obvious to me, right?
That’s a good point! I definitely agree about that effect.
That said, I think that the effect is bidirectional. Antisocial tendencies cause negative reactions to the person and negative reactions to the person strengthen antisocial tendencies. For example, I’ve heard people express anecdotes like “I realized I was being an asshole and tried to better myself, but then nobody noticed and everybody treated me like I hadn’t changed at all, so I gave up on even trying” or “I was always an asshole so nobody gave me a chance, but then this one person showed up who believed in me even though I kept being a jerk to them, so then I eventually stopped being so much of a jerk to them, and over time I became less of a jerk overall”.
One weakly-held intuition would be that if it’s very hard for parents to overcome their instinctive tendency to react more harshly to a difficult kid, such that almost nobody manages it, then this would show up as a hereditary effect (if the saintly parents who can respond to every child will equal warmth are as rare as the monstrous ones who abuse their kids terribly). And I do think it’s very difficult to overcome that tendency, such that very few people manage it! I like kids and can usually sympathize with even some of the more challenging ones, but it’s still a lot easier for me to show and feel pure positive regard toward the intrinsically easy and friendly ones.
… but that’s only weakly held, because I do acknowledge the point that some parents are still much more patient or harsh than others, so you would expect that to show up as a shared environment effect nonetheless. So I have to fall back on “maybe there is an effect, but it’s counterintuitively unpredictable”. But even then we’d have to disregard the Waller et al. 2018 study, which doesn’t say that the effect would be weirdly unpredictable.
Is there any action-relevant difference between “no effect” and “no predictable effect”?
”Shared Environment” measures to what extent children raised in the same household wind up more similar than children raised in different households. If tailoring your parenting approach to each child helps children develop more agency, happiness, etc., and some households have parents that do this more/better than others, then it would show up as a Shared Environment effect on measures related to agency, happiness, etc.
The influence of individualized parenting would appear in the error term of the twin study model, which is typically interpreted as “unshared environment,” or events impacting one twin but not the other. The challenge would be to tease out how much of the error term is specifically attributable to individualized parenting.
So basically the right kind of parenting is not considered “parenting” for the purpose of the studies?
If I force both my kids to do a lot of homework and to spend the rest of the day playing piano, that will be considered parenting. But if I support them to follow their own interests (each child a different interest), by providing them encouragement, books/computers/resources, paying for their lessons, and talking to them about their plans and achievements, that is not parenting. Did I get that right?
I for one know that I interact very differently with children with different personalities! (Or, for that matter, with adults with different personalities.) One classic example of this is that children who are naturally compliant and “easy” are disciplined/punished less, because there’s much less of a need to do so.
Yeah equating parenting with shared-environment can lead to confusion, but your example doesn’t necessarily end up in the non-shared part I think. If the personality of the child was mostly downstream of the genes, then I think that would still end up in shared environment and would not be a problem (You treat both twins the same, because they have about the same temperament). If some parents treat twins differently because of “random” things like which twin left the womb first and is considered firstborn, which baby hit their head, inherent contingency in personality etc., then yeah, I think that would end up in a non-shared environment if you do twin experiments.
I just recently ran into someone posting this on Twitter and it blew my mind:
Claude at least basically confirmed this interpretation (it says it is “slightly overstated” but then gives a “clarification” that doesn’t change it). My reaction was “wait WHAT”—doesn’t that completely invalidate the whole “parenting doesn’t significantly matter for future life outcomes” claim?
Because that claim is based on equating “parenting” with “shared environment”. But if you equate “parenting” with just “what are the ways in which parents treat each child identically” then it seems that of course that will only have a small effect.
I for one know that I interact very differently with children with different personalities! (Or, for that matter, with adults with different personalities.) One classic example of this is that children who are naturally compliant and “easy” are disciplined/punished less, because there’s much less of a need to do so.
I would intuitively expect that the amount of ways in which parents treat each child exactly the same would be very small. As an extreme case, parents who engage in child abuse may sometimes be abusive toward only some of their children, while treating the rest more or less normally; e.g. because some of the children have traits that the parents happen to intensely dislike. Even if we don’t go that far, most parents will get along better with some of their children than others. One child might be more on the same wavelength with mom while their sibling is more on the same wavelength with dad, etc.
How isn’t this talked about more as an enormous caveat to those “parenting doesn’t matter” studies? (ping @Steven Byrnes )
Claude Opus 4 on non-shared environment claim
is this accurate:
“An intriguing feature of twin studies: anything a parent does to individualize for a child is non-shared-environment (NSE) rather than shared environment (SE). and when people claim twin studies show parenting doesn’t matter, they’re conflating parenting with shared-environment when non-shared-environment contains parenting too.”
This is largely accurate, but needs some clarification.
The statement correctly identifies that differential parenting—when parents treat their children differently—gets categorized as non-shared environment (NSE) in twin studies. This is indeed a crucial point that’s often misunderstood.
However, the claim that “anything a parent does to individualize for a child is NSE” is slightly overstated. More precisely:
Shared environment (SE) includes parenting behaviors that affect all children in a family similarly—like general parenting style, family rules, socioeconomic status, neighborhood, etc.
Non-shared environment (NSE) includes parenting behaviors that differ between children—like favoritism, different responses to each child’s temperament, birth order effects, or tailoring approaches to each child’s needs.
The second part is spot-on: when people claim “twin studies show parenting doesn’t matter,” they’re often making the error of equating all parenting with shared environment. Since shared environment typically shows small effects in many twin studies (especially for personality traits and IQ in adults), they conclude parenting is unimportant. But this ignores that differential parenting is captured in the non-shared environment component, which often shows substantial effects.
This is a sophisticated critique of how twin study results are commonly misinterpreted. The reality is that parenting can matter enormously—it’s just that the ways parents adapt to and treat each child individually may matter more than their general parenting approach that applies to all children equally.
Claude Opus 4 on factors causing differential parenting
Parents naturally:
Respond to each child’s temperament differently
Adjust discipline strategies based on what works for each child
Have different relationship qualities with different children
Spend different amounts of time with each child based on needs/interests
Express affection differently based on each child’s preferences
Set different expectations based on each child’s abilities
Child characteristics:
Age/developmental stage—Parents adapt their approach as each child grows, so siblings experience different parenting at the same chronological age
Gender—Despite intentions, parents often interact differently with boys vs. girls
Physical appearance—Children who resemble a favored (or disfavored) relative may be treated differently
Health/disabilities—A child with chronic illness, ADHD, learning disabilities, etc. often receives different parenting
Birth order—Firstborns often get more anxious/intensive parenting; later children more relaxed parenting
Temperament match—An extroverted parent might click better with their outgoing child than their introverted one
Situational factors:
Parental life circumstances—Parents going through divorce, job loss, depression, etc. during one child’s formative years but not another’s
Family composition changes—Only children who later get siblings experience very different early years
Economic changes—One child might grow up during prosperity, another during financial hardship
Parental learning—Parents often say they were “different parents” to their younger children after learning from mistakes
Relationship dynamics:
Goodness of fit—Some parent-child pairs just “click” better due to shared interests, communication styles, humor
Behavioral cycles—A difficult child may elicit harsher parenting, which increases difficulty, creating a feedback loop
Triangulation—In some families, one child becomes the “peacemaker” or “scapegoat,” receiving distinct treatment
Identification—Parents may see themselves in one child more than another, leading to different expectations/treatment
Unintentional differences:
Parental energy/age—A 25-year-old parent has different energy than a 40-year-old parent
Comparison effects—Parents may push a child harder (or less) based on their siblings’ achievements
Time availability—Work schedules, other children’s needs, etc. affect how much one-on-one time each child gets
All of these create non-shared environment effects in twin studies, yet they’re clearly parenting factors that could significantly impact outcomes.
Like I always say, the context in which you’re bringing up heritability matters. It seems that the context here is something like:
If that’s the context, then I basically disagree. Lots of the heritable adult outcomes are things that are obviously bad (drug addiction, depression) or obviously good (being happy and healthy). Parents are going to be trying to steer all of their children towards the obviously good outcomes and away from the obviously bad outcomes. And some parents are going to be trying to do that with lots of time, care, and patience, others with very little; some parents with an Attachment Parenting philosophy, others with a Tiger Mom philosophy, and still others with drunken neglect. If a parent is better-than-average at increasing the odds that one of their children has the good outcomes and avoids the bad outcomes, then common sense would suggest that this same parent can do the same for their other children too, at least better than chance. That doesn’t require an assumption that the parents are doing the exact same things for all their children. It’s just saying that a parent who can respond well to the needs of one kid would probably (i.e. more-than-chance) respond well to the needs of another kid, whatever they are, whereas the (e.g. drunk and negligent) parents who are poor at responding to the needs of one kid are probably (i.e. more-than-chance) worse-than-average at responding to the needs of another kid.
And yet, the twin and adoption studies show that shared environmental effects are ≈0 for obviously good and obviously bad adult outcomes, just like pretty much every other kind of adult outcome.
In other words, nobody is questioning that a parent can be abusive towards one child but not another. Rather, it would be awfully strange if a parent who was abusive towards one child was abusive towards another child at exactly the population average rate. There’s gonna be a correlation! And we learn something important from the fact that this correlation in child-rearing has immeasurably small impact on adult outcomes.
Likewise, adoptive siblings may have different screen time limitations, parents attending or not attending their football games, eating organic versus non-organic food, parents flying off the handle at them, being in a better or worse school district, etc. But they sure are gonna be substantially correlated, right?
So I think that the argument for “the bio-determinist child-rearing rule of thumb” goes through. (Although it has various caveats as discussed at that link.)
My context is most strongly the one where I’m trying to reconcile the claims from therapy vs. heredity. I know we did already agree on one particular mechanism by which they could be reconciled, but just that by itself doesn’t feel like it would explain some of the therapy claims where very specific things seem to be passed on from parents.
But yeah, I think that does roughly correspond to arguing over whether the bio-determinist child-rearing rule of thumb applies or not.
On one hand, this does make sense. On the other hand—as far as I know, even the researchers who argue for the strongest bio-determinist case will make the caveat that of course none of this applies to cases of sufficiently extreme abuse, which will obviously mess someone up.
But… if that is in fact the case, shouldn’t it by your argument show up as a shared environment effect?
I can think of a few different explanations:
Even extreme childhood abuse doesn’t have a major effect on life outcomes.
(Including this one for completeness though I consider it obviously implausible.)
The level of abuse that would affect life outcomes is rare enough not to be picked up on in the studies.
The methodology of the studies creates on floor on the badness of outcomes that gets picked up; e.g. maybe adoptive parents are screened well enough to make the worst abuse not happen, and the people drawn from national twin registers and contacted to fill in surveys don’t bother responding if their lives are so messed up they don’t have the time or energy for that.
But at least studies that use national registers about e.g. incarceration should be able to control for this.
There’s something wrong about the correlation argument.
When I asked Claude about this, it claimed that actually, studies done with national registers find a significant shared environment effect on antisocial behavior and criminality. It gave me this cite which reports a 26% shared environment effect on antisocial behavior defined as various forms of crime (property offenses, violent offenses, and drug-related offenses), measured from childhood to early adulthood [20 years], and also cited some previous work with similar findings.
I wasn’t sure whether that study was at all representative or cherry-picked so I looked at studies citing it and found this paper on antisocial behavior specifically, which has this mention:
Which sounds like even identical twins may be treated differently enough by the same parents for it to have noticeable effects?
Will Eden’s blog post that Buck linked to below mentions that
So given all of that, when you say
Then maybe this is wrong, at least when we restrict the range of parenting to not-obviously-horribly-abusive which doesn’t seem to get clearly picked up for whatever reason. I agree that it’s certainly weird and counterintuitive that it’s wrong, but I’m not sure that explaining it by “maybe parents just have a minimal effect overall” makes things any less weird and counterintuitive!
Conditional on there only being a small-ish shared environment effect, “even parents who try their best may easily screw up and be unable to overcome their own emotional issues enough to provide consistent parenting to all of their kids” doesn’t sound less implausible to me than “parenting just has no effect”.
It’s easy for me to imagine that e.g. a parent who pushes their children to socialize may benefit some of their children in the long-term while overwhelming their more introvert or socially anxious kids; that a parent that leans neurotypical vs. autistic could have an intuitive understanding of their kids who are like them but end up not parenting the unlike-them kids well; that a parent would relate significantly differently to their girls than their boys; and so on.
Also I suspect that reducing things to a single spectrum of “does one’s parenting have good or bad effects” is too simplistic. For instance, Eliezer has a post where he mentions that:
Now I think that this is too strong—you can probably become a rationalist even without that kind of a background—but if we accept that this was the origin story for some rationalists, then… growing up in a cult or having a clinically insane parent, so that your “core emotional trust in the sanity of the people around you” is broken, certainly sounds like it should have an overall “bad effect”. And probably it does have some bad effects. But on the other hand, if it also makes you into an upstanding critical thinker, that probably contributes to good outcomes? Which of those effects dominates? Idk, probably depends a lot on your environment and how lucky you get and it could go either way.
In therapy there’s also the finding that different people may respond to exactly the same issue with the opposite emotional strategies, so if two children grew up in a cult, maybe one of them would lose all capability for critical thinking and the other would become a super-rationalist. This could be partially driven by genetic factors, but then if their parents didn’t join a cult, those same genetics would probably lead to more moderate outcomes.
So rather than going with the bio-determinist rule of thumb that “things you do as a parent will have generally small or zero effects on what the kid will be like as an adult”, maybe it’s more like “things you do as a parent will have generally small or zero predictable effects on what the kid will be like as an adult”—if your kids had gotten a different set of parents, they might get significantly different outcomes, but there’s no clear way of predicting how those outcomes are different. With you as their parent, your son gets outcomes [good A, bad B, neutral C] and your daughter gets [good A, neutral B, bad C]; with some other parent, your son would get [neutral A, bad B, good C] and your daughter would get [good A, bad B, neutral C].
Thanks!
I vote for the second one—the result is usually “shared environment effects on adult outcomes are statistically indistinguishable from zero” but that doesn’t mean they’re exactly 0.00000…. :)
There are definitely huge shared environment effects during the period where kids are living with their parents. No question about it!
(Also, for the record, some measurements seem to be adult outcomes, but are also partly measuring stuff that happened when kids were living with their parents—e.g. “having ever attended college”, “having ever been depressed”, “having ever gotten arrested”, etc. Those tend to have big shared environment effects too.)
The result there is “parents are harsher and less warm towards their kids who are more callous and aggressive”, and when you phrase it that way, it seems to me that the obvious explanation is that parents behave in a way that is responsive to a kid’s personality.
Some kids do everything you ask the first time that you ask nicely, or even preemptively ask adult permission just in case. Other kids are gleefully defiant and limit-testing all the time. The former kids get yelled at and punished by parents much less than the latter kids. (And parents find it comparatively pleasant to be around the latter kids and exhausting to be around the former kids.) This all seems very obvious to me, right?
Thus, if per Will Eden “parents think they treat their kids the same… but the kids think the parents treat them differently, and outside observations would support this claim”, I’d guess that the parent would say something like: “the household rule is: I’ll watch TV at night with any child who wants to do that and who sits quietly during the show, and another household rule is: if you jump on the couch then you have to go to your room, etc. I apply these rules consistently to all my children”. And the parent is correct—they are in fact pretty consistent in applying those rules. But meanwhile, the kids and outside observers just notice that one sibling winds up getting punished all the time and never joining in the evening TV, while the other sibling is never punished and always welcome for TV.
In my post I poked fun at a study in the same genre as Waller et al. 2018. I wrote: “I propose that the authors of that paper should be banned from further research until they have had two or more children.” Of course, for all I know, they have lots of kids, and they have babysat and hung out with diverse classes of preschoolers and kids (as I have), and yet they still subscribe to this way of thinking. I find it baffling how people can look at the same world and interpret it so differently. ¯\_(ツ)_/¯
Anyway, that other study didn’t even mention the (IMO primary and obvious) causal pathway from child personality to parental treatment at all, IIRC. The Waller et al. 2018 study does a bit better: it mentions something like that pathway, albeit with an unnecessarily-exotic description: “Evocative rGE reflects situations in which the child elicits an environment consonant with his/her genes (e.g., a callous child frequently rejects parental warmth, causing his/her parents to eventually reduce their levels of warmth).”), and they claim that their study design controls for it. What they mean is actually that they (imperfectly) controlled for the “child genes → child personality → parental treatment” pathway (because the children are identical twins). But they don’t control for the “random fluctuations in such-and-such molecular signaling pathway during brain development or whatever → child personality → parental treatment” pathway. I find that pathway much more plausible than their implied preferred causal pathway of (I guess) “parents are systematically warmer towards one twin than another, just randomly, for absolutely no upstream reason at all → child personality”. Right?
I think the only way to see parental effects without getting tripped up by the child personality → parental treatment pathway is to rely on the fact that some parents are much more patient or harsh than others, which (my common sense says) is a huge source of variation. Just look around and see how differently different parents, different babysitters, different teachers interact with the very same child. That brings us to adoption studies, which find that parenting effects on adult outcomes are indistinguishable from zero. So I’m inclined to trust that finding over the studies like Waller et al. 2018.
By the way, Will Eden cites Plomin, but meanwhile Turkheimer reviews many of the same studies and says the results are basically zero (he calls this “the gloomy prospect”). (Turkheimer is Plomin’s reference 41.) It would be interesting to read them side-by-side and figure out why they disagree and who to believe—I haven’t done that myself.
I don’t find these things counterintuitive, but rather obvious common sense. I can talk a bit about where I’m coming from.
There are many things that I did as a kid, and when I was an adult I found that I didn’t enjoy doing them or find it satisfying, so I stopped doing them. Likewise, I’ve “tried on” a lot of personalities and behaviors in my life as an independent adult—I can think of times and relationships in which I tried out being kind, mean, shy, outgoing, frank, dishonest, impulsive, cautious, you name it. The ways-of-being that felt good and right, I kept doing, the ones that felt bad and wrong, I stopped. This is the picture I suggested in Heritability, Behaviorism, and Within-Lifetime RL, and feels very intuitive to me.
Also, my personality and values are very very different from either my parents’ personalities, or the personality that my parents would have wanted to instill in me.
I guess the childhood trauma thing is important to your intuitions, which we were chatting about in the comments of my post. I can share my first-person perspective on that too: I was blessed with a childhood free of any abuse or trauma. But I’m kinda neurotic, and consequently have wound up with very very dumb memories that feel rather traumatic to me and painful to think about. There is absolutely no good reason for these memories to feel that way—I’m thinking of perfectly fine and normal teenage things that I have no objective reason to be embarrassed about, things in the same ballpark as “my parents walked on me masturbating, and promptly apologized for not knocking and politely left, and never brought it up again”. (My actual painful memories are even dumber than that!) Just as you were speculating in that comment thread, I think I’m predisposed to dwell on certain types of negative memories (I’m very big into embarrassment and guilt), and in the absence of any actual objectively terrible memories to grab onto, my brain has grabbed onto stupid random teenager stuff.
I am able to take the harsh edge off these memories by CBT-type techniques, although I haven’t really bothered to do that much because I’m lazy and busy and AFAICT those memories are not affecting my current behavior too much. (I’m somewhat introverted in part from being oversensitive to social embarrassment and guilt, but it’s not that bad, and my uninformed guess is that finding peace with my dumb teenage memories wouldn’t help much.)
Is there any action-relevant difference between “no effect” and “no predictable effect”?
Thanks!
Hmm, I think it might be good to sharpen the context a bit more, as I feel we might be slightly talking past each other.
The argument that I’m the most focused on questioning is, to be clear, one that you haven’t made and which isn’t in your writings on this topic. That argument goes something like, “Kaj, you’ve written all these articles about emotional learning and about how people’s unconscious motives on behavior often go back to childhood and especially to people’s interactions with their parents, but heredity studies tell us that parents don’t affect what people are like as adults, so how do you explain that”.
And it gets a bit subtle since there are actually several different versions of that question:
“Therapy books sometimes give the impression that everything about a person’s life is determined based on their childhood circumstances. How do you justify that, given twin studies?”—Very fair question! Some therapy books do give that impression, and such a claim is clearly incorrect. I’m not going to defend that claim. I think it’s basically a result of selection bias. The people who got lucky enough with their genes that they make it through sucky childhoods without major issues don’t see therapists, and then therapists write books that draw on their clinical experience based on clients that have been selected for having unlucky genes.
“Okay, but even if not everything about a person’s issues is determined by their childhood circumstances, the therapy books still say that stuff like parental warmth is a major factor on a person’s future psychology. But wouldn’t that imply a bigger shared environment effect?”—Also a very fair question, and the thing that I’m the most interested in figuring out/explaining! And I’m trying to explain that with something like “maybe parents have counterintuitively different effects on different children, and also the specific psychological issues this may cause don’t necessarily map linearly to the kinds of outcome variables the studies are looking at”.
“So from twin studies, we know that parents have basically no causal effect whatsoever on the children, so...”—Okay now my imagined interlocutor is going too far, the twin studies don’t say that. Parents still have some causal effects on their children—such as the children having memories of being raised by their parents, that would be different if they’d had different parents! But, I’ve talked with some people who did seem to take their interpretation of the studies that far! So I’d like to at least establish an argument that makes it clear why that is wrong.
And as an aside, when I say “therapy books”, I also mean my own personal experience with coaching people and applying the kinds of techniques the therapy books talk about. Quite often childhood stuff or stuff about parents pops up, even when the questions I ask don’t reference childhood in any way.
So when you say that
Then, on the one hand, I do agree with your reasoning here, and what you say also agrees with my own experience of what I’m like as an adult vs. what my parents are like.
On the other hand, when talking about the study of adolescent/young adult antisociality, you mention that parents do have a significant effect on their children when the children are still living with them. And it’d be pretty weird if the degree of adolescent/young adult antisociality had no effect on what one is like as an adult. That’s especially so since the measure of antisociality in this study was, basically, “has the person committed property crimes, violent crimes, or drug-related crimes”.
From the perspective of questions #2 and #3, I might say: “Whether you commit crimes as an adolescent has to have some predictive effect on your future outcomes. Obviously it’s not a deterministic effect—even if you deal drugs as a teenager and beat someone up for not paying their drug debt to you, it’s still totally possible to put all of that behind you and end up as a well-adjusted adult. But you would expect such a person to be statistically less likely to end up with good outcomes than someone who committed zero crimes in their teens, right?”
“So I’m honestly a little confused how to reconcile ‘significant shared environment effect on crime when an adolescent’ with ‘basically no shared environment effect on adult outcomes’. But maybe it’s just the case that serious crime as youth is pretty rare in the first place, and not getting over it is more rare still! (Especially given that the study covered people who grew up in Sweden ca. 1985-2006.) Still, I would expect that the people who used to commit crime as teenagers will have a different psychological profile than the people who never did, even if their background ends up ultimately not affecting the coarse kinds of variables that the other twin studies measure. For instance, maybe they feel shame and guilt about what they’ve done and will want to process that with a therapist later, or maybe they have some anxiety of their past catching up on them… even if neither of those is the kind of thing that’d be picked up on the twin studies. So I feel like that should answer the skeptical voice asking questions #2 and #3.”
To take another example—when I was a kid, I wore shoes with no laces on them and somehow nobody taught me to tie my shoelaces until I got to a point where it was embarrassing not to know how to do it. As a defensive move, I made it into an identity thing that “I’m not the kind of person who uses shoes with laces”. I continued with that way all the way until I was about to turn 30, at which point I finally acknowledged that I was being stupid, looked up some YouTube video titled “the easiest way to teach your kid to tie their shoelaces”, and taught myself to tie shoelaces.
I’m pretty sure there was a causal connection between that sequence of events and me having the parents that I had, since some other parents would just have taught me to tie my shoelaces earlier. And it had a slight negative effect on my self-esteem during that time. But again neither of those was the kind of a thing that would be picked up on twin studies. (Especially since I don’t have a twin, but never mind that.)
That’s a good point! I definitely agree about that effect.
That said, I think that the effect is bidirectional. Antisocial tendencies cause negative reactions to the person and negative reactions to the person strengthen antisocial tendencies. For example, I’ve heard people express anecdotes like “I realized I was being an asshole and tried to better myself, but then nobody noticed and everybody treated me like I hadn’t changed at all, so I gave up on even trying” or “I was always an asshole so nobody gave me a chance, but then this one person showed up who believed in me even though I kept being a jerk to them, so then I eventually stopped being so much of a jerk to them, and over time I became less of a jerk overall”.
One weakly-held intuition would be that if it’s very hard for parents to overcome their instinctive tendency to react more harshly to a difficult kid, such that almost nobody manages it, then this would show up as a hereditary effect (if the saintly parents who can respond to every child will equal warmth are as rare as the monstrous ones who abuse their kids terribly). And I do think it’s very difficult to overcome that tendency, such that very few people manage it! I like kids and can usually sympathize with even some of the more challenging ones, but it’s still a lot easier for me to show and feel pure positive regard toward the intrinsically easy and friendly ones.
… but that’s only weakly held, because I do acknowledge the point that some parents are still much more patient or harsh than others, so you would expect that to show up as a shared environment effect nonetheless. So I have to fall back on “maybe there is an effect, but it’s counterintuitively unpredictable”. But even then we’d have to disregard the Waller et al. 2018 study, which doesn’t say that the effect would be weirdly unpredictable.
For parents, you mean? None that I can think of.
Will Eden, long-time rationalist, wrote about this in 2013 here.
Seems misleading.
”Shared Environment” measures to what extent children raised in the same household wind up more similar than children raised in different households. If tailoring your parenting approach to each child helps children develop more agency, happiness, etc., and some households have parents that do this more/better than others, then it would show up as a Shared Environment effect on measures related to agency, happiness, etc.
The influence of individualized parenting would appear in the error term of the twin study model, which is typically interpreted as “unshared environment,” or events impacting one twin but not the other. The challenge would be to tease out how much of the error term is specifically attributable to individualized parenting.
So basically the right kind of parenting is not considered “parenting” for the purpose of the studies?
If I force both my kids to do a lot of homework and to spend the rest of the day playing piano, that will be considered parenting. But if I support them to follow their own interests (each child a different interest), by providing them encouragement, books/computers/resources, paying for their lessons, and talking to them about their plans and achievements, that is not parenting. Did I get that right?
Yeah equating parenting with shared-environment can lead to confusion, but your example doesn’t necessarily end up in the non-shared part I think. If the personality of the child was mostly downstream of the genes, then I think that would still end up in shared environment and would not be a problem (You treat both twins the same, because they have about the same temperament). If some parents treat twins differently because of “random” things like which twin left the womb first and is considered firstborn, which baby hit their head, inherent contingency in personality etc., then yeah, I think that would end up in a non-shared environment if you do twin experiments.