In my earlier post on Gregory Clark’s work, The Son Becomes The Father, I laid bare the case for the known high heritability of human behavioral traits (including values and attitudes) and life outcomes. As well, equally important, I illustrated the complete absence of shared environment influences on these – that is, the effect common environmental forces that children growing up together share. This includes parents and upbringing, making it abundantly clear that parents don’t leave a lasting impact on who we grow up to be. These are towards what I’m calling the “75-0-25 or something” rule, which echos Satoshi Kanazawa’s “50-0-50 rule” summarizing behavioral genetic research, only more accurately so. This “75-0-25 or something” rule means the following:
For the variance in behavioral traits and life outcomes, each factor accounts for the following fractions:
- Heredity: 75% (though the variance is typically anywhere from 65% to almost 100%)
- Shared environment: 0%
- Unknown (classified as the “unique environment” or the “unshared environment”): 25%
About that third component, the unexplained variance, or the “unique environment,” we have thus far failed to reliably find anything that can account for it. It is deemed “environmental” in the sense that it is not heritable and presumably not genetic in origin (although that is not likely entirely accurate), but we have no idea what factors comprise it.
It’s important to note these values only represent the estimates within a generation. It doesn’t necessarily hold between generations (or between other contexts), where gross environmental changes can and do have large effects on the manifestation of human traits. See my post Why HBD. (Anyone who fails to absorb this gets an automatic F grade.)
However, the large heritability estimates and the failure to find any reliable environmental modulates of within-cohort differences casts doubt on most any environmental theory. Quite likely, as with the case with diet and lifestyle (see Tweet of the Week), most of the ones you’ve heard are bunk. It seems likely that the human genome draws up a design for a certain organism (that is more or less faithfully executed) that is designed to function to process and negotiate its environment in a certain set of ways, and precise behavior depends on the circumstances of the day and the specifics of the situation (see my post Environmental Hereditarianism). This may be as good of an explanation as any, but I am looking for evidence of reliable environmental modulation. One apparent environmental modulation is that some individuals with certain sensitive temperaments may be permanent modified by certain environmental exposure. Post-traumatic stress disorder (PTSD), for example, appears to be highly heritable. As well, it seems only certain individuals are susceptible, even after experiencing traumatic events. This illustrates that the susceptibility and extent of environmental modification of human traits is bounded by genetic prescription.
The high heritability of behavioral traits and the general lack of environmental effect on human behavioral traits (along with knowledge of the past and evolutionary theory) also leads one to understand that differences between human groups, be those groups be races, nationalities, ethnic groups, regional populations, even clans/families (as with Gregory Clark’s work), must also have some (rather large) genetic basis. “Culture” then is to be understood as the collective manifestation of those differences – the product of each individual’s innate propensity acting on each other’s and the circumstances of the day. Hence, genetic factors underlie these divisions:
For the above reasons, this should be a given, but, we see how that is received in this day and age.
Even for those who accept heritable human differences, there is some discomfort at their full implications. My earlier post More Twitter Wisdom featured discussion of the unease many people have with this notion. Ironically, this itself is due to heritable factors (and yes, for those who can’t connect the dots, the ease that I have with this idea is in part the product of my genetic inheritance). Some people fight this notion tooth and nail, often eschewing logic in the process. Useful information can come out of these discussions, however, and this post will be an example. A recent troll commenter took that track, and here I will answer his claims.
Heritability, as established by behavioral genetics, comes from multiple lines of evidence, spanning completely different study methods. Most poignant today are Genome-wide Complex Trait Analyses (GCTA), which look at the correlation between resemblance in phenotype to directly measured resemblance in genotype. These have confirmed the (additive, anyway) heritable contribution to traits like IQ, BMI, and alcoholism, etc. However, even before these direct analyses came on the scene, the older methods firmly established the high heritability of behavioral and cognitive traits.
The bulk of behavioral genetic studies compare identical twins (monozygotic, MZ) raised together with fraternal (dizygotic, DZ) twins raised together. This is a particularly powerful method, because you control for a vast array of confounds, down to shared uterine environment. The difference in similarity between MZ twins and DZ twins estimates heritability. However, this method has weaknesses. It truly can’t rule out shared environmental influences as being behind the twin correlation. And further still, even to the extent that it produces a shared environment measure, it can’t separate the effect of assortative mating from this (which inflates the DZ twin correlation). You need confirmation from other methods. And such other methods exist.
The most “pure,” in terms of assessing heritability, are studies looking at twins raised apart (MZA and DZA, as opposed to MZT and DZT). Indeed MZA studies give you direct measurements of the heritability estimate. Additionally, there are adoption studies, which – when looking at adopted siblings – give you a direct measurement of the shared environment. Other pedigree studies (full siblings vs half-sibs, sibs vs. adoptees) buttress these. And finally, the extended twin design, which look at not just twins, but parents, spouses, cousins, etc. can allow you to separate a variety of influences.
One study gives a chart neatly summarizing the results of all of these for IQ:
This is from The Wilson Effect: The Increase in Heritability of IQ With Age (2013). The heritability of IQ in adulthood from large samples of twins reliably returns in the 0.8 range. As we see here, a few studies, including a reasonably sized (n ~ 500) from Sweden that was a MZT-MZA-DZT-DZA study found a heritability of IQ of 0.91 at age 65. One study (a biological sibling-adoption study, small sample though) found a heritability pushing 100%!
As seen here, adoption studies confirm the high heritability of adult IQ.
MZA studies, which are few and small, also confirm this. An apparent gap between the heritability found in MZA studies and the others is seen here. However, the combined sample size of MZA studies is only 187! The average heritability estimate from these of 0.74 is not horrendously off when one considers the small sample sizes.
The high early shared environment influence shows that in youth, environmental factors can make a difference. These influences diminish and disappear with time, dashing hopes of lasting parental influence. Some voices – including preeminent behavioral geneticist Robert Plomin himself – often try to claim that the increasing heritability of IQ and other behavioral traits can be boiled down to “gene-environment correlations” (rGE). The idea being that people seek out environments to suit their genetic proclivities (which they do), and the influence of that environment leads to the final trait. This is a nice rosy idea, because it appears to leave the door open to environmental manipulation, if we could intervene in the “proper” ways. However, it is fantasy. We clearly saw in my earlier post that the “gene-environment co-variance” was often negative! One’s environment seemed to be “making” one the opposite of what one would expect. Our experiences don’t shape our political attitudes like we think they do. So is the case with IQ.
Indeed, a meta-analysis of longitudinal twin and adoption studies attempted to test this idea. It sought to determine whether the increasing heritability of IQ could be explained by on-going environmental influence or genetic “amplification”; that is, the compounding of genetic effects over time. This is likely because the effect of each additional gene becomes more and more relevant as children grow up. Indeed, amplification is what they found:
Another criticism of the heritability of IQ is that it is modulated by socioeconomic status (SES) – that IQ is less heritable in poor families. A large and extensive study co-authored by Robert Plomin reviewed the literature on the gene-SES interaction and conducted their own analysis of this phenomenon (with a sample of 8,716 twin pairs) and found no such effect. The heritability was constant across SES, but the shared environment vs. unique environment varied (this was done on children).
As well, for the record, though the overwhelming bulk of data for behavioral genetic studies comes from Northwestern European countries and their derivatives, behavioral genetic results have been gathered outside the Western world. The same results for the genetic and environmental influences on IQ has been found in Japan, for example (additive heritable influence, A ~ 0.8; shared environment, C = 0). This is in line with other behavioral genetic results generated there and in South Korea, as mentioned in my earlier post. Many behavioral genetic studies are underway outside the West, and we should have these results soon.
But on that point, another criticism leveled at behavioral genetic studies is that, in the United States at least, IQ is less heritable for racial minorities such as Blacks and Hispanics. However, this too is false. Over at Human Varieties, analyses by bloggers Chuck and Dalliard (also here) found no modulation of the heritability of IQ by race.
Proponents of the efficacy of nurture – especially parenting – often repeat a few erroneous arguments. Here I will address them. One of them is the idea that parenting, while ineffective for most, may make a difference for individuals with certain temperaments. For example, perhaps the low IQ/shiftless/delinquent/criminal or otherwise poorly dispositioned might benefit from more authoritative parenting, say. It’s a nice idea to think about, but it doesn’t happen. This is essentially “Stolen Generations” wisdom. As we’ve seen in my earlier post, a massive review of twin and adoption studies found no significant shared environment effect on criminality in adults (well, modeling found a shared environment contribution of 0.09, which can generally regard to be non-significant given the enormous measurement error expected). Even an effect that operated on some children but not others would contribute to the overall average shared environment, which was negligible.
Indeed, also supporting this is another massive meta-analysis of behavioral genetic influences on adolescent psychopathology (personality disorders). These captures various types of child misbehavior and dysfunction, including convenient diagnoses such as “oppositional-defiant disorder.” A look and the breakdown of their results is far more interesting than their main reported results. Typically, shared environment effects are seen in children (<18 years old). The main study reported this, but fortunately, they decomposed the type of measurements used. In addition to self-report and parental report, they also had teacher report, peer reports, and clinical diagnoses. The self and parental reports showed lower heritabilities (0.3-0.5) and significant (though small) shared environment components. However, when teacher or peer reports were used, they found much higher heritabilities, in the 0.65-0.8 range. As well, the shared environment impact vanished. Using clinical diagnosis also produced a zero shared environment impact. Considering the sheer size of this review, it’s clear that parental behavior don’t contribute to this malaise, even at these ages.
The problem of somewhat unreliable measurements (noise), especially coming from self-report, was illustrated in my earlier posts. Averaged peer ratings serve to adjust for this problem to an extent both by providing more proper social context by which to make accurate comparative ratings and by cancelling out fluke readings. Indeed, one behavioral genetic study, which attempted to investigate the idea of a “general factor of personality” (GFP), akin to g for cognitive ability, found that when using the combined scores of self and peer ratings, the heritabilities of the Big Five personality traits shot through the roof, with the additive heritable component being:
- Extraversion: 0.86
- Openness: 0.92
- Neuroticism: 0.59
- Agreeableness: 0.85
- Conscientiousness: 0.81
This demonstrates that more accurate measurements consistently push up the heritability estimate (even pushing them towards 100%), giving us the basis of the 75-0-25 or something rule.
As for the sixth dimension of personality, “honesty-humility”, the H component of the six factor HEXACO, evidence of its high heritability is also established, as we saw previously. Indeed, a recent post by Peter Frost (Evo and Proud: Compliance with moral norms: a partly heritable trait?) discussed a twin study from Sweden that looked at various forms of dishonesty, such as fraudulently claiming sick benefits or evading taxes. And sure enough, these particular behaviors showed considerable heritability. There is a desperate need for cross cultural behavioral genetic analyses. Many dimensions of personality systems like the HEXACO (as imperfect as they are) are likely to systematically vary from culture to culture.
The usefulness of behavioral genetics – indeed, the single most powerful and solid area of all social science – is highly evident. But behavioral genetic methods can be used to address several long-standing questions. Here we see it’s clear that parents don’t leave much of an impact on our behavioral traits. But what about people who aren’t parents? Here I will look at two sets of important people, spouses and peers.
It is no secret that spouses correlate on behavioral traits. This, assortative mating, is a powerful force, as we’ve seen previously. There are two aspects where spouses are highly correlated – the things you don’t talk about in a bar: politics and religion. Some have assumed that a good bit of this is because spouses grow more similar with time. But is this the case?
This is where the “extended twin” design comes in handy. One large study (N > 20,000) in particular looked at precisely that. By including twins, their spouses, and parents, etc, they were able to directly measure assortative mating. What did they find? Spouses were correlated for several traits. But the traits they were most correlated in were political orientation and religiosity. Social “homogamy” (having the same background as your spouse) couldn’t explain this, as the correlation between MZ twins and their co-twin’s spouse were consistently higher than that of DZ twins, and so on. As well, spouses weren’t influencing each other, as the correlation between spouses was not affected by length of the marriage (even when only couples married <2 years were examined).
The study was also able to lay to rest another persistent myth. We’ve heard that we choose spouses like our opposite sex parent (like our mothers for men and like our fathers for women). Anyone who’s remotely genetically informed should be able to see that this could just be due to choosing mates like ourselves. And so is the case. As the authors put it:
there was no evidence for the sexual imprinting hypothesis. Twins’ partners were not significantly more similar in any trait to the twin’s opposite-sex parent than to the twin’s same-sex parent or a DZ co-twin of either sex, nor was there even a trend in this direction
These results were also consistent with the Peter Hatemi et al extended twin study on political attitudes featured previously.
The similarity between spouses has nothing to do with mutual influence, but assortment. At least this bit is common sense. I suspect few long married individuals will believe that they changed their spouse.
On that note, a key theory put forward by the woman who first elucidated the non effect of parents, Judith Rich Harris, was that the unique environment “influence” might be boiled down to peer influence. Staffan did a nice recap of Harris’s theory (see The Nurture Enigma – How Does the Environment Influence Human Nature? | Staffan’s Personality Blog). We all have heard of peer pressure. And indeed, peers seem to be an important force when it comes to language and behaviors like smoking initiation. But do peers really have this great influence, as Harris posits? Well, as I posted over at the Lion of the Blogosphere:
Most research into peer effects is confounded by the same thing that standard parenting studies are: inability to control for the effect of heredity.
A behavioral genetic study (on the Add Health data) that looked specifically at GPA and found that 72% of the similarity between U.S. high school students and their peers could be explained by genetic factors. In other words, school performance and the apparent peer “influence” is really just kids choosing to associate with kids of similar intelligence and motivation:
Peers seem like a fine avenue to get excited about, because it seemed like a vehicle through which parents could assert some influence. But, when you really consider it, peers can’t really be all that important in the long run, because if there were systematic effects of peers on adult outcomes, it’d turn up in the shared environment, which it doesn’t. One could posit that the effect of peers is completely random, but if that were true (aside from the major violation of Occam’s Razor that presents), why worry about it?
The “75-0-25 or something” rule is robust and reliable. This instructs that should we find some major deviation from this, it can be taken to be a sign something is seriously amiss. We saw that with male homosexuality (see Greg Cochran’s “Gay Germ” Hypothesis – An Exercise in the Power of Germs). Now I will discuss two curious exceptions to this pattern.
One rather astonishing example was the heritability of social trust. A behavioral genetic study out of the Netherlands found that the heritability of trust in others, as measured by:
The trust-in-others and trust-in-self scales were designed to include three items that were central in existing scales … thereby capturing items with positive valence (“I completely trust most other people”) and negative valence (“When push comes to shove, I do not trust most other people”), both of which explicitly used the word “trust”, and an item that captured the broad behavioral implication of the trust: the intention to accept vulnerability, as explicated in one of the most widely-accepted definitions of trust … (“I dare to put my fate in the hands of most other people”)
…found no significant heritable influence on these. The extent that people trusted, at least as captured by these measures, was virtually entirely a function of the unique environment.
This was a puzzling result. The clear pattern of the high heritability of all behavioral traits was established, as I’ve discussed. So how could a propensity to trust not also be influenced by genetic factors? One explanation touted around was that trust is contingent on experience; if we found people trustworthy, we would trust. If we didn’t, we would not. While that might sound convincing, the trouble is that the same could be said for many other behavioral traits. Is general trust less socially contingent than say bigoted feelings against some groups, like homophobia (which is at least 54% heritable)? That seems rather unreasonable.
One key question: how do they assess “trust”? Just how good was their measurement? Measurements in social science need to meet three basic criteria: they need to be reliable (that is multiple testing instances of the same individual should give roughly the same results), they need to be “valid” (that is, be predictive of some real-world outcome), and they should be heritable. This trust measure clearly fails on the third criterion. However, the study authors claim the test-retest correlation was good, so it is reliable. But what about the second? Does this trust measure actually predict anything?
To find out, I looked at a study that sought to answer that very question. This study, done in Germany, looked in detail at the reliability and the validity of their measurement of trust, a measurement very similar to the Dutch study. The noted a key point, one HBD Chick will appreciate. That is, trust is multi-faceted. There is trust in institutions, which is distinct from trust in known others, which is distinct from trust in strangers (I’d imagine HBD Chick would break it down one more, and separate “known others” into family and non-family). But more importantly, to question of validity, they assessed this by the correlation between trust in strangers and trusting behavior in the “dictator game.” They found a correlation, but only with trust in strangers.
But their correlation was very small (Spearman’s = 0.17) – and this is with a game which itself has questionable relation to trust behavior in the real world. I suspect that their instrument is not predictive of any trusting behavior in the real world. It’s worth mentioning another (fairly small) study of the heritability of trust from Australia found a non-insignificant heritability, though a smallish one (0.14-0.31).
The situation with trust is unclear. But this brings me to another example of a feature for which the heritability estimate appears to be trivial. That is the female G-spot. A study on about 1,800 female twins from Britain found that the heritability of the reported presence of a G-spot wasn’t significant. The result was virtually entirely unshared environment. Debate has raged on as to whether or not the female G spot exists at all, but that is to be expected, since research into human sexual behavior is among the most difficult to conduct properly. But, the result from this study indicating that the G spot isn’t heritable is puzzling. If the G spot was a real anatomical feature, and one that wasn’t universal, then one would expect a rather significant heritable impact. The finding that it’s not heritable points to one of two conclusions. One, perhaps the G-spot is in fact universal, but only some women have “discovered” it. That seems rather implausible, given the rather significant variation in heritable morphological features of sex organs in women. The second possibility is that the G-spot in fact doesn’t exist at all, and women who claim to have one are mistaken. That seems more likely, but I wouldn’t want to completely dismiss the claims of women who state they have such a feature. The mystery remains.
The findings of behavioral genetics, particularly the highly significant impact of heredity and the absence of shared environment effects, in addition to the complete failure to find reliable environmental sources that contribute to the “unique environment” component of the variance, calls into question virtually every pet environmental theory that has been put forward. It guides one to be suspicious of most “environmental” explanations of behavior. Now, let me be clear, I am not saying that these environmental influences don’t exist. I am not saying that if they do exist, we won’t be able to ever find them. I am also not saying that development doesn’t require a complex interplay between genes and environment. Try going without food, water, air, or speaking to another person if you don’t believe me. I am also not saying that the secular changes in human traits that are brought about by gross environmental changes don’t happen. The increase in average height over the past century disproves that. But what I am saying is that you should be doubtful of most pet theories of how the environment influences us, especially those that promise we can control, or sometimes even predict it. For as we see, that’s far from an easy task.
Note the similarity between these songs:
What is the tune that all these songs feature? Is it an established musical device? Was there a prototypical song upon which all these songs are based? Anyone who has an idea, please do let me know.
Courtesy “misdreavus,” “cold russian,” and HBD Chick:
Knowing how much of your lifelong outcomes can be determined by a string of nucleotides is a most distressing thought—
misdreavus (@SuperMisdreavus) April 09, 2014
To which (correctly) responded “cold russian”:
And HBD Chick:
I for one am fully aware that a big part of the backlash against behavioral genetics and HBD (from both the Left and Right) comes because it clashes with the self concept of some people. One issue is the degree of “control” one feels one has in one’s life. This is part of reason I’m given a hard time when I talk about the nonexistence of free will. Another aspect is that we all have a worldview of some kind, one which is not entirely based on facts. Some people are emotionally invested in certain pre-conceived notions about how the world is – specifically, how we are. This is through no fault of their own; that’s how they are. However, unfortunately, many of these individuals don’t take too kindly to the facts. But what can you do?
There is one thing I can say, to counteract one charge I frequently get:
Some folks believe genes = determinism. That's a false choice. Determinism was always the case. Genetics are just one of its agents.—
JayMan (@JayMan471) February 23, 2014
Well said! I spotted it in a conversation with Dennis Mangan. I guess it’s good to see that someone else has brought up these points.
Here’s the rest of the conversation:
Unfortunately, it seems, Dennis Mangan – like many in the medical establishment – appears permanently locked into a rather unscientific way of thinking. The problem of disentangling correlation and causation is ignored. Uncontrolled observational studies are taken as proof of whatever medical fad in vogue at the time. It is possible to “control” for various variables (since we can surely think of all the relevant ones) to see if the variable of interest is a causal factor.
James Thompson had a recent post on research conducted in this matter (Psychological comments: Is it healthier to eat 7 vegetables or 7 scientists?). Thompson references an article written by David Colquhoun, where Colquhoun references the work of John Ioannidis (here Colquohoun, quoting Ioannidis):
The gist is given by the memorable statement
“Almost every single nutrient imaginable has peer reviewed publications associating it with almost any outcome.”
and the subtitle
“Definitive solutions won’t come from another million observational papers or small randomized trials“.
Colquhoun lays bare the problem:
The problem, of course, is that humans are very good at attributing causality when it does not exist. That has led to confusion between correlation and cause on an industrial scale, not least in attempts to work out the effects of diet on health.
The likely truth:
We can probably say by now that no individual food carries a large risk, or affords very much protection. The fact that we are looking for quite small effects means that even when RCTs are possible huge samples will be needed to get clear answers. Most RCTs are too short, and too small (under-powered) and that leads to overestimation of the size of effects.
and what must be done:
The best thing that can be done in the short term is to stop doing large observational studies altogether. It’s now clear that inferences made from them are likely to be wrong.
At the very least, it would seem to me there’s one idea that would be a very helpful step in the right direction:
Correlational health studies would be more impressive (and useful) if they included IQ and personality data.—
JayMan (@JayMan471) April 06, 2014
As for this particular finding, the apparent link between depression and processed food consumption, assuming it’s real at all, what’s behind it? Well, what does processed food consumption correlate with (hint: negatively)? IQ. This is indeed the subject of James Thomspons’ latest post (IQ, Neuroticism, booze, and those damn vegetables again).
On that, one very large study (of Swedish conscripts) found that IQ was negatively correlated with severe depression (and other things like schizophrenia). So there’s that, anyway.
Previously: Gary Taubes on Obesity and Bad Science
For some reason, this seemed appropriate:
Thanks to a persistent troll, I’ve enabled first-time comment moderation. New commenters will be required to have their very first comment approved by me. After that, you may comment freely. This means you won’t be able to leave the name box blank if you want to be able to comment without moderation. An e-mail address is NOT required.
A vigorous discussion has been triggered by the release of Gregory Clark’s The Son Also Rises: Surnames and the History of Social Mobility. In this book, Clark details his work which shows a large transmission of status from generation to generation, all across the world, going back centuries. The discussion has raged on the mode of this transmission. How does it occur? Clark found that when you look at surnames, which trace paternal lineages, you find that the status of families today is related to their status centuries ago. That is, surnames associated with high status in the past are over-represented among high status individuals today, and vice versa. This pattern holds across much of the world, from England, to Sweden, to Japan, to Korea, to China, to Chile. The pattern goes back centuries – Normans surnames are still overrepresented among the English elite. The descendants of the samurai still dominate the Japanese upper classes. The intergenerational correlation of status – a measure that includes wealth, education, occupation, longevity, etc (i.e., the “good stuff” of life), was as high as 0.8 in Clark’s analysis. Clark did find that regression to the mean occurred; high-status families became less high-status with time and vice versa, but it took a very long time – 10 to 15 generations, to for them to get there.
See this talk by Greg Clark, where he explaining his findings:
But why does the pattern that Clark found occur? That remains a key point of debate. Does it occur because of genetic inheritance of traits that lead one to success or failure (which include IQ, determination, cunning, physical health, attractiveness, etc.)? Or does it occur because of the advantage (or lack there of) conferred by one’s family status (e.g., a leg up into prestigious schools, the direct effect of wealth, connections, etc.)?
Greg Cochran and Henry Harpending have both shared their analyses of the situation:
Cochran on it:
In the short run, from one generation to the next, luck plays a big role. In the longer run, the fact that the subpopulation being examined has a different genotypic average, one more likely to result in high status, means that regression to the mean of the general population is slow for the subgroup, essentially caused by gradual change in its average genotype, change produced by intermarriage with individuals who on average have a less favorable genotype. Other than high heritability, the other prerequisite for this pattern is highly assortative mating for moxie. If two groups have different average amounts of moxie, complete endogamy (as in Indian castes) would ensure that the between-group difference would continue indefinitely, disregarding selection.
So is that it? Is this long-term transmission of legacy genetic? It appears that way. The pattern that we see is much what one would expect of a lineage over time if, collectively, the additive genetic components of this success factor was largely passed on from one generation to the next. Indeed, it really shouldn’t be any different. The individual variation is caused by a variety of factors, including environmental “luck”, non-additive genetic effects, developmental noise, and spousal genetic contribution (which may help or hinder). But, the key point, when the whole clan is considered at once, all these sources of variance should more or less cancel out. The only thing that breeds true is the additive genetic variance, and, in any large clan, that should pass on fairly uninterrupted from one generation to the next. The whole clan’s short-term generation-to-generation variance can be caused by variation in local circumstances that may help or hinder the entire lineage. That too should, over the generations, cancel out, in good part. The success of the clan over time is then dictated by its evolutionary fitness and the degree of assortative mating.
Assortative mating is key to perpetuating this process. The more assortative mating there is, the more each clan (which, by the way, is a fitting term in this instance, even for NW European societies, where there are no “clans” in HBD Chick‘s sense) retains the genes for success (or failure) and the slower the regression to mean. Non-assortative mating is the hole through which genes leak out over time, hastening regression and familial turn-over throughout the ages.
So what of these genetic traits that are germane to success? What are they? IQ is definitely one of them, and perhaps the single most important. But there are others, physical health surely, attractiveness likely, certain personality traits, such as conscientiousness, as well as not so admirable traits, such as those on the Dark Triad(Tetrad) (i.e., narcissism, Machiavellianism, psychopathy, sadism), especially Machiavellianism. Maybe we could describe an “m” (moxie) factor (analogous to the g factor) that underlies them all (and maybe this gives credence to the idea that there is a “general factor of personality”). Of course, as we know, a number of these traits (e.g., conscientiousness, attractiveness, health) are positively correlated with IQ, so there’s that.
After all, what gives us this pattern?
That I will leave to others to hash out. For my contribution, I wanted to zoom in a bit on a more local level and look at our particular snapshot in time, and examine something that should give commenters on this matter (and everyone else with an interest in this) pause.
The idea that this transmission of status over time has been as Clark found it squares well with another facet I discuss frequently on this blog: the fact that parenting doesn’t have much of a lasting effect on children’s outcomes.
That’s right, all the things parents do for their children, beyond the incredibly demanding task of keeping children alive and healthy, doesn’t count for much in the long run. We know this because of the absence of shared environment effects on children’s outcomes: children do not resemble the people they grow up with once you subtract the effects of heredity. Yes, the similarity between parents and child relative to the environment as a whole is completely due to shared genes. See my posts All Human Behavioral Traits are Heritable and Taming the “Tiger Mom” and Tackling the Parenting Myth for more on the mechanics of this.
The interesting thing is that even the people who take me seriously on this point still believe that there’s something their efforts can do, beyond keeping their children fed, clothed, clean, and cognizant of the basic ways of the world. Steven Sailer frequently suggests that the outcome of poorer children, especially those of color (mostly Hispanics) would improve if they had fewer of them, and hence could afford to invest more in each, despite the fact that this doesn’t hold up in adoption studies.
And to be sure, parents play and have played an important role in passing on skills and knowledge to their children. This is often a long and highly involved process, but, as most any parent knows, a rewarding one. But though parents play this vital role, when it comes to how our kids turn out, it’s best to think of it as “you can lead a horse to water….” The child’s innate abilities and proclivities, plus whatever developmental luck he or she possesses, will guide his or her path through the world.
However, a lot of parents – especially in the West today – feel one of their biggest goals is to see that their children receive the best education possible. Education unlocks many of the goodies in society today, and as such, it’s typically best that a child maximize his educational attainment to do best in life.
This is something where parents – even those aware of the non-effect of parenting – often innately feel that they have a role to play. And they may be justified in thinking so.
A large meta-analysis of behavioral genetic studies of educational attainment performed across much of the developed world (Australia, Britain, Germany, Italy, Denmark, Finland, Norway, Sweden, Spain, and the United States) found a significant and fairly substantial shared environment component to adult educational attainment. They found that the shared environment accounted for, all told, 36% of the variance in adult educational attainment, and 24% when only people born after 1950 were considered.
Interesting, isn’t it? Very interesting, you might think. Some may be quick to declare that this invalidates all that have been saying about the non-effect of parenting. Since education is something that clearly “matters” so much in life, then parents should redouble their efforts, right?
Well, it actually turns out that it doesn’t quite work that way.
There are actually quite a few complications to this, and quite likely this doesn’t mean what it appears to mean. For one, “educational attainment” is often measured in these studies as either a quantitative variable (years of schooling completed) or a categorical one (degree attained). It doesn’t add in the obvious complication of where and how. A quick look at the previous chart of transmission of income by occupation should be one clue. Another clue is this chart by Razib Khan, that makes it abundantly clear not every bachelor’s degree is created equal:
See also this SAT to IQ conversion of various college majors. We see a big difference between physics, astronomy, mathematics, and engineering majors on one end, with average IQs in the 125-135 range, and social work, early childhood, student counseling on the other, with average IQs barely above 100. I’d wager that if you were to decompose the “rigor” of the degree attained by major and by prestige of the institution that awarded it, the shared environment component would disappear. I’ll leave this for a future project.
It’s also worth mentioning also that “shared environment”, while it would be where you’d look to find the effects of parents and upbringing, doesn’t necessarily mean parents. We see this with studies of smoking initiation (which often occurs in teenage years). The extended twin family design, which looks not just at twins, but their parents, grandparents, non-twin siblings, avuncular relatives, etc., can decompose the “parental” shared environment from the “non-parental” shared environment. This study found that “cultural transmission” (i.e., from parents) couldn’t explain the pattern seen in children (indeed, the parent-child correlation was negative once you removed heredity). The non-parental environment explained the variance, suggesting that other influences, such as peers, likely explain the results.
Another major issue with the finding of a nonzero shared environment effect exists. This issue squares the matter with Gregory Clark’s results. That is, when you consider other facets, education per se doesn’t seem to mean much in the end. Apparently, you can’t teach moxie. This is revealed by the fact that every trait “going in” that shapes a person (and should be relevant to educational attainment) reliably shows absolutely no shared environment impact. This includes not just the most well-known example, IQ…
…but personality traits, and not just some “broad major personality dimensions”, I mean highly specific behaviors, and including one’s work preferences and interests, the presence or absence of mental disorders, and including the features of a person we think of as “character.” Parents leave no lasting effect on any of it, aside from what they bequeath to their children genetically. See this review of the behavioral genetic evidence by Thomas Bouchard and Matt McGue, as well as this one by Bouchard. The high heritability and zero shared environment is also seen in the Dark Triad(Tetrad) traits as well, as seen in this meta-analysis of the heritability psychopathic traits.
It’s worth mentioning that many of these studies don’t partition out measurement error, that is, inaccuracies in the assessment of the traits to be analyzed. This has the effect of attenuating the heritability estimate. Other studies, which use methods to get around that problem, find heritabilities for personality traits in the 0.7-0.8 range, as is found for IQ, mental disorders, and physiological variables like height and BMI.
The significance of measurement error brings me to another thing. Sure, parenting might have no effect on intelligence or behavioral characteristics, but what about “values” and “beliefs,” the things many parents hope to instill in their children? Well, there’s no effect of the shared environment there, either. We see this for overall religiosity and religious values. (A note here, a review of behavioral genetic studies on this found that there was a non-insignificant shared environment component to religiosity in adults. However, religious beliefs and convictions are traits for which assortative mating is very strong – indeed, my wife and I are both atheists, and so are my wife’s sister and her husband. This would have the effect of erroneously inflating the shared environment estimate at the expense of the heritability estimate in MZ twin-DZ twin studies. One study in the review compared MZ twins raised apart with those raised together. It found a zero shared environment, making it likely that assortative mating is behind the non-trivial shared environment finding in MZT/DZT studies). We also see this with political beliefs, as found by Peter Hatemi et al’s massive meta-analysis across five countries, and with their “extended family design” twin study, which included a longitudinal component, allowing for both the partitioning of any shared environment findings and accommodation of the effects of assortative mating and measurement error:
Indeed, when we consider the effect of measurement error (adding it to the heritability estimate and to the somewhat nonsensical negative gene-environment correlation values), the heritability of political attitudes and social values skyrockets, being upwards of 85% (74%) for views towards pornography in women (men). The heritability of overall political orientation, when accounting for measurement error, teeters on 100%!
Liberals and conservatives will be battling for a long time to come.
So as we see, the heritability of everything that goes into forming a person is high, the shared environment, which represents the effects of parents, is zero. (It’s worth mentioning for those who are unfamiliar with these terms that there is also a “unique environment” term, which tends to be somewhere between 50-20% or so, typically lower once you account for measurement error. Hence the “shared environment” ≠ “all environment.”)
By the way, these findings don’t just hold in Western countries. The high heritability of and nil shared environment impact on behavioral traits are also found in Japan and South Korea. These East Asian cultures – with vastly different attitudes towards parenting – show the same pattern of heritable and shared environment influence as do Westerners.
But that’s all OK, yes? The whole point of education is to “shape” the raw individual beyond his/her genetic predilection, right? Wrong.
The problem is that everything that comes out, the adult outcomes, shows a shared environment impact that is also zero. These include:
- Criminality (massive meta-analysis of twin and adoption studies shows insignificant shared environment effect in adults)
- Marital stability/divorce risk (WW II and Vietnam era twin registry and Minnesota twins study)
- Substance abuse (review of meta analyses – high heritabilities in the 0.6-0.75 range, 0 shared environment for alcoholism, cannabis use, cocaine, and heroin)
- Tobacco smoking (meta analysis – shared environment impact on initiation, as explained above; no impact on persistence)
- “Sociosexuality” (promiscuity) (Australian twin registry study)
All the major outcomes don’t seem to show any lasting impact from whatever the shared environment impact on educational attainment is. But, most damning of all, a large meta-analysis covering the U.S., Australia, and Sweden has found that the shared environment impact on lifetime income is also zero! The very thing most hope education will translate into appears to depend more on the individual’s innate traits – “moxie“ – and luck – than any special benefit conferred by mere degree. Whatever shared environment influence there is on educational attainment, like so many other things, it doesn’t seem to matter in the long run.
OK, so you might be willing to accept that you can’t shape your child’s personality or values. You can’t control his major life outcomes. You can’t even control how much money he will go on to earn. But surely you can do something useful, like leave your children a lifetime of happiness, right? After all, I believe, and advise, that a parent’s key duty, after ensuring that their children grow up healthy and safe, is to ensure that each has a happy childhood. Surely that must count for something, too,? It does, in the form of fond memories of childhood.
For it turns out that overall life satisfaction as an adult has a high heritability and a shared environment impact that is also zero, as found in a Dutch twin study and in a Norwegian one, together with a combined sample size of over 12,000. One’s lifetime of happiness boils down to genes and to the fickleness of luck.
Some of you might wonder how I could be a parent and believe that my efforts in raising my child will not impact who goes on to become. Well, I’ve long since known that it was out of my hands. He will be who he will be. It’s only my job to help him get there, and pass on the legacies of all those who came before him. I did all I could do: I married well. Beyond that it’s in the hands of “fate”.
The failure of parents to appreciably affect the outcomes of their children affirms Gregory Clark’s findings, and indicates that much of the transmission of status from one generation to the next is ultimately genetic in origin. Clark’s studies used several measures of status, and I haven’t covered them all here. Perhaps something reliably affected by the shared environment might yet turn up. I’m not betting on it though.
Almost certainly, throughout history, and across the diverse societies, there has been a huge amount of “noise” in the transmission of status, especially on the individual level and in the short run. The vagaries of the circumstances no doubt imbued good fortune on some and dashed the success of many others. But through it all, the thing that is at the root of continuity – DNA – remained the active ingredient to propagate lineages in their respective places through out the ages.
It is as it was said in the Richard Donner Superman films: “The son becomes the father, and father becomes the son.” That encapsulates the essence of the reality here. Underneath all the variability (much of which is driven by more or less random forces), there is a fundamental truth in those words.
As for the theme for this post, I can’t think of anything more appropriate than “Jaga’s Theme.” This tune symbolizes both survival and the passage of knowledge and a legacy from one generation to the next. It is perfectly fitting.