Counterintuitive, Episode 7: Resolution – Parents, Peers, and How Millions of Twins can Turn Your World Upside Down

The final Counterintuitive episode of the three-part miniseries about human nature is online! After tackling preferences & personality, we now weigh in on the debate about nature vs. nurture to find out how we become who we are. If you like this episode, be sure to check out other episodes on Spotify, Apple Podcasts, Stitcher, TuneIn, YouTube, or SoundCloud (or basically every place where you can get podcasts). Below, you’ll find the transcript of this episode with some references / further reading hyperlinks. The music for this episode comes from FreeSound. At this point it is basically “music by Setuniman“, because that’s really great music! Specifically these pieces:



In the fourth century before Christ, Aristotle, pupil of Plato and often referred to as the father of Western philosophy, was the defining figure in the Greece of antiquity. Unbeknownst to many, Aristotle also dabbled in Greek tragedy, the main form of theatre back in the day. In his book Poetics, he noted that the typical Greek tragedy consists of five parts, two parts introducing the audience to the story and three acts for telling the actual story. A beginning, a middle, and an end. Sounds trivial but even today most screenplays, and stories in general, follow this course. Because it works.

By now the three-act structure has been solidified and extended, with the presence of a situation-changing incident in Act I – think a first encounter between future spouses or an unexpected inheritance – and the introduction of tension and excitement in Act II, trouble in paradise for instance. Act III then contains the climax, the ultimate settling of the question of the play: Will they or won’t they? Will the main character find happiness in the end? If you don’t want to call them Act I, II, III, they also have other names: Setup, Confrontation, and Resolution. This is Act III, this is Resolution, this is the climax.


You’re listening to episode seven of Counterintuitive, the podcast about things which are not what they seem to be. My name is Daniel Bojar and we are right now in the final episode of this miniseries about human nature. In the span of these three episodes, I wanted to investigate human nature, find out how the current research consensus aligns with intuitive beliefs about human nature, and, finally, make a case for a new conceptual view of our nature. Because, and we will get to that in the next episode, concepts and mechanism are always more abstract, always more counterintuitive than we intuitively believe. Because it would be the most extreme expression of anthropocentric hubris to think that intuitive or simple explanations could even remotely capture reality.

In the first episode of this miniseries we probed our preferences, with the conclusion that preferences can only considered to be stable if you accept the extreme context dependence of preferences. Then, in the second episode, personality was the main topic, specifically its stability across contexts. And of course a similar picture to preferences emerged: incredibly high variance, incredibly high context importance. These revelations have thrown up a couple of important questions: Are we one or are we many? Who are we truly? We’ve answered these questions at least partially in the last two episodes. Today, we add to these answers and we also add a new question into the mix: How do we become who we are? Yes, you’ve got it: we’re talking about nature vs. nurture here. Welcome to Act III, welcome to the climax.


It all started with a 2015 article in the journal Nature Genetics. In fact, a meta-analysis by lead author Tinca Polderman, corresponding authors Peter Visscher and Danielle Posthuma, and collaborators, based in the Netherlands and Australia. Polderman and her colleagues took on the gargantuan task of sifting through thousands of scientific publications, in order to find the type of studies they were interested in analyzing. Twin studies which investigated complex human traits. Traits like personality aspects, cognitive functioning, weight maintenance, etc. etc. They ended up with more than 2500 publications, basically all twin studies published in that topic between 1958 and 2012, more than 50 years of twin study research! Just to give you a sense of scale: that corresponded to close to 18 000 investigated human traits and 14.5 million twin pairs from 39 different countries. The results of this meta-analysis might offend you or just lead to flat-out denial. But before doubting the results of this meta-analysis, which we’ll go into in a minute, please ask yourself if your psychological pet theory has 14.5 million study participants in its corner and how much data you think is enough to settle a question.

Why then are twin studies so all-important for investigating complex human traits? Twin studies usually compare genetically identical twins who either grew up in different households or in the same household. That’s really great because it basically eliminates genetics as a confounding factor. You can then even compare these twins with fraternal twins, whose DNA is not the same, similar to normal siblings, to find out what effect genetics plays. Since identical twins have the exact same genes, any difference between them growing up apart or together must come from their environment. Twin studies are the gold standard in the nature vs. nurture debate. From these studies come all the results you probably heard of already, like for instance that traits are on average about 50 percent heritable. This is oftentimes transformed into the one-size-fits-all “it’s about fifty-fifty nature and nurture”. And I won’t argue too much with that number. What I will argue with, however, is what we mean by ‘nurture’.

Unsurprisingly, Polderman and her colleagues found that not a single trait of their close to 18 000 investigated traits had no genetic influence. Fair enough, we are at ease with the notion that genetics has some influence, even though it’s currently popular to downplay its importance. What about nurture though? Technically, nurture should be synonymous with ‘environment’. Yet, at least in the way we typically use it, we mean child rearing when we say nurture. Psychologists use a handy notation to distinguish these different types of nurture: They speak of ‘shared environment’ for the effects your parents or siblings have on you. Shared, because a set of twins growing up in the same household necessarily shares this environment. On the other hand, the term ‘non-shared environment’ is used to describe the effects of the rest of your environment (peers, school, etc.). Because even for identical twins, their friends are not necessarily shared. How about you venture a guess which one of the two is more important? Shared environment, with parents and siblings, or non-shared environment, with peers, the media, and school? Here’s a hint: This show isn’t called Counterintuitive for no reason.

You might even be fine with non-shared environment playing a somewhat larger role than shared environment but that’s not what Polderman and her collaborators found. After combing through all the studies their conclusion was this: For about 70 percent of their traits, that corresponds to over 12 000 complex human traits, no influence of shared environment was found. None. Put another way, for the majority of your traits, including personality and values, neither your parents nor your siblings matter. At all. Or maybe that’s not strictly true. Their genes matter, just not whatever they do during child-rearing. All the ‘nurture’ effects in these 70 percent comes from non-shared environment, for instance from your peers. Of course there are the other 30 percent of traits, in which shared environment plays at least some role, such as how spiritual you are, but if you take any random trait it’s much more likely that how your parents raised you didn’t affect you in that trait.

Now that’s a lot to unpack and I’m sure it meets a lot of mental resistance in most people. Because the alternative, that how you were raised is important for your personality and values, is just so intuitive and so unshakeable. So let’s first give you all the stabilizing information I can give you. Parents certainly can impart knowledge or skills to their children through education. They can also certainly give their child a happy childhood which is worthwhile regardless of whether this leads to any positive change in their personality or values. They just don’t have any substantial influence on their personality or values.

One of the immediate objections most likely is going to be the plethora of research indicating otherwise. Countless publications demonstrating the effects education by one’s parents can have on later life. For instance, parents who abuse their children increase the chances of their children to be abusive parents and partners themselves later on. But notice the trap here. ‘Increasing the chances’ would mean that the parental behavior causes the later increase in the behavior of their children. Yet what most people, and unfortunately most psychological articles, forget is that parents share about 50 percent of their DNA with their children. So, a priori, it is expected that children are, to some extent, like their parents because they are directly related and share a substantial portion of their genetic information. This is precisely where twin studies come into play again. Because, in studies, genetically identical twins are in most traits similar to the same degree, regardless of whether they grew up together or in different households. If parental education would make a substantial difference, you would expect twins who grow up in the same household with the same parents to be more similar than twins growing up separately. Yet even though these twins share genetics and shared environment, they’re not more similar than twins merely sharing genetics. Even more shocking, adopted children are not more similar to their new siblings after growing up with them than two random kids from the street!

This result, based on millions and millions of twins and thousands of academic publications, is our climax. Parental education (and interaction with your siblings) does not form your personality, values, and most other traits in a substantial manner. Now onto the resolution. For this, we’ll answer two questions: how is this possible & why does it happen like that? First, how.

Here, we can draw on the last two episodes, on the extreme context-dependence of preferences and personality. I hope by now we have successfully eroded any belief in a stable or intrinsically true personality and preferences. Effectively, in every new context we learn anew how to act, how to react, and how to be. And there are so many different contexts. You can observe that when you speak to your parents as an adult. If you’re anything like the typical person, you act characteristically different than when speaking to a friend or to your boss. In a way, you become more childlike again: don’t act out, don’t use swear words, respect the parental authority (at least to some degree). Or, more precisely, you act more childlike again. It’s just another context, with a corresponding personality. And as it’s not the exact same context as when you were a child, you don’t act exactly as you did when you were a child. Since your parental context only describes one context among many which you will encounter during your life, you wouldn’t expect that the behavior learned at home would be characteristic overall. One way you can see this is that a stronger parental influence on personality can be seen while the child is living at home (even though it basically vanishes once the child moves out). Because at that point, the context at home is one of the most dominant contexts in the life of a child and better represents their overall life than in adulthood. Even here though, you can ascertain that the behavior at home is just a reaction to context and not some intrinsic personality. Studies show, for instance, that there is very little correlation between rule-breaking behavior at school and at home. Two very different contexts, two very different personalities.

Another, often neglected, factor is the indirect influence of genetics. I’m talking about the power of genetics to sway your choice of environment. Let’s say you’re smart. Being smart is at least 50 percent genetically determined. But being smart also leads you to associate with other smart people, to perhaps choose a more intellectually stimulating type of work, and to engage in lifelong learning. These are all environmental factors but they’re made more likely by your genetic basis of intelligence. You can demonstrate that with data, as the fraction of your IQ that can be explained by your genetics steadily increases throughout your life, concordant with the idea that your DNA has a seeping influence on your environment. The fifty-fifty split between nature and nurture with regard to IQ is only true in adolescence. In old age, however, genetics explains about 80 percent of your IQ score.

One part of this environment which you, to some extent, choose are your peers. And as a substantial part of your nonshared environment, they of course have an influence on many of your traits. Studies show, for instance, that attitudes about school (whether you care about school or if you’re too cool for school) and other attitudes change after you change your group of friends. Of course your attitude changes in a way that it afterwards resembles the attitude of your new friends. You fit into your new peer group because exclusion from a group carries an evolutionary penalty with it.

Now, you might ask, why is it that this value and trait adaptation stemming from fear of exclusion takes place in peer groups but not in your family? That brings us to the second question: Why does shared environment (aka parents and siblings) have no substantial influence on your character? Because of course exclusion from your family group should be even more deadly evolutionarily speaking. But there are two broad counterarguments to this. First, prehistoric humans did not engage in the careful childrearing we can observe today. As can be seen in hunter-gatherer societies today, children did not receive special attention and were left to the care of elder siblings or other children. They were taught to not speak to adults if not spoken to, and were not imbued with a carefully selected assortment of values by their parents as is the case today. So, evolutionarily speaking, it would be suicide if a child relies on receiving all or even most of its traits, values, and personality from their parents. Rather, the focus should be on other children, preferably elder children, because that’s where they will spend most of their time. Today, younger children are however no longer entrusted to their older siblings for nurture. Rather, sibling rivalries are flourishing and can even be exacerbated by their parents.

The second counterargument applies both to the prehistoric as well as our current age. It refers to the fact that peer environments are much more characteristic for the average life situation you face in adulthood. While living at home, a child is in a clear power imbalance and has to obey the commands of their parents. Yet, later, when you’re with friends or with your partner, little to no power imbalance can be observed. Therefore, building peer group-compatible values and traits is more important overall than building the same for a power imbalance scenario as in your childhood. Your trait acquisition therefore accurately reflects your needs in life and your overall characteristic environment. Here’s another scientific nugget which nicely illustrates this point: Children with less contact to peers were shown to have lower pro-social behavior but the number of siblings (or absence of siblings) did not influence the number of friends a child had. The conclusion seems clear. Children learn their social skills from their peer-friends, not from their parents, nor from their siblings. Because the social skills you learn from your parents are only useful in power imbalance contexts, not in peer contexts which dominate your life once you exit your parental home.

Even conservative estimates locate the timespan containing the most dramatic changes to our personality as extending to our thirties. For most people, this gives you a full decade of development outside the influence zone of your parents. So even just considering this should lead us to question the dominance of parental influence. And change doesn’t stop at age thirty, as we have seen in the preceding episodes. Instead, it’s happening all the time. Not only are we multifaceted with regard to all kinds of contexts, we’re also continuously evolving with time. The moral of the story? Maybe don’t blame parents for how their children turned out, the next time around. But also, don’t praise them too much if their children turned out well. Because, frankly, their influence on all of that is really limited. Because each of us is many and our intricate yet flexible nature cannot be conclusively explained by a single source of influence. Because sometimes even the most intuitive sources of influence don’t matter all that much.


And now we are at the end of this miniseries about human nature! If you want to find out more about this fascinating topic, consider reading The Nurture Assumption by Judith Rich Harris, an excellent and in-depth book which yielded much of the inspiration for this series. In two weeks, we will reconvene to dedicate ourselves to the question of why it’s beneficial to think about counterintuitives in the first place. As always, references and further reading for this episode can be found in the linked show notes. If you like this or other episodes, please consider sharing them with your friends and subscribe on Spotify, Apple Podcasts, or wherever you get your podcast from. Every second Thursday a new episode will be uploaded. My name is Daniel Bojar and you’ve listened to Counterintuitive, the critical thinking podcast about things which are not what they seem to be. You can follow me on Twitter at @daniel_bojar or on my website, where you will find other counterintuitive articles. Until next time!

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