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513C5X3UhAL._AC_UL320_SR220,320_ As one might expect, the piece that I co-authored with Brian Boutwell, Heritability and why Parents (but not Parenting) Matter, has stirred up some irritation and even anger. Part of this is simply due to the mildly hyperbolic nature of the title. Obviously on some level parents matter a great deal. What we were attempting to get at though is that most parents have far less precise control of the outcomes of their children than they think they do (you do have great control if you beat or starve your children though!). The lack of control is one reason siblings vary so much.

To make it concrete, imagine across the population variation of personality is 30% heritable, 15% accounted for by shared environment, and 55% explained by non-shared environment. The parental effect is captured in the shared environment. When behavior geneticists downplay the role of parents in affecting outcomes, they are doing so because of this value. In this example the proportion explained by the parents’ genetic variation is twice as large as the conscious environmental choices. But, note that most of the variation is not necessarily due to genetic factors!

What is this variation? The short answer is that we don’t know. One hypothesis, promoted by Judith Rich Harris in The Nurture Assumption, is that it is one’s social milieu. That is, peer groups. To my knowledge in the past 15 years there has not been much support for this thesis, suggesting to me that we’re still at a loss to explain non-shared environment. In fact it may just be an intractable stochastic aspect of life outcomes (or if you want to reduce it to biology, developmental stochasticity).

People become uncomfortable with these statistics because they suggest that the most immediate personal control you can have on the character of your offspring is through the spouse you select. Your spouse (or you) may change values over time, but you are not going to change your genes. This is not very congenial with the modern American conservative orthodoxy that crystallized after World War 2 which placed the nuclear family at the center of the culture (basically, fusionism). The rise of “family values” as inoculation against liberal permissiveness is to a great extent predicated on the idea that shared environment is very powerful over the long term. The data just don’t support this proposition.

We can see this when you look through recent history. Some of the response to the Quillette piece emphasized and reiterated that we missed something when we ignore and dismiss the importance of values that parents’ instill in their children. But values are malleable. A whole generation of Southerners grew up in the 1950s and 1960s with racial values taught to them by their parents, and they also grew out of those values as a generational cohort. Or, look what’s happening with gay marriage: …Evangelicals Are Changing Their Minds on Gay Marriage:

The shift is especially visible among young evangelicals under age 35, a near majority of whom now support same-sex marriage. And gay student organizations have recently formed at Christian colleges across the country, including flagship evangelical campuses such as Wheaton College in Illinois and Baylor in Texas.

Obviously this goes back to Judith Rich Harris’ general insight: social consensus and cultural cognition are real phenomena which are enormously impactful. But please remember that this doesn’t necessarily explain non-shared environment, as these sorts of dynamics are forces for conformity and homogenization. When we are thinking about control of outcomes, usually you need to focus on:

– Culture
– Genes
– Parents

In that order. The non-shared environmental variance will still be substantial, but we don’t have a good sense of what’s causing it yet. And we may never. But we can choose a lot of life outcomes by selecting the nation we migrate to, or, by the community with which we identify. For example, if I migrated back to Bangladesh and raised my daughter to be a staunch atheist with a generally liberal-individualist ethos, those values might stick. There’s probably some heritable aspect to my character which makes atheism and liberal-individualism “a good fit.” But, there is a strong chance that my daughter will conform to the milieu in which she grows up, and with which she may identify. The exception to this would be if she found a subculture which insulated her from broader social conformity pressures, and allowed her to develop her worth and identity differently.

I’m not totally sure of the political implications of this perspective in the United States. My own position is that the rhetoric of “family values” on the American Right today has been strongly suffused with an individualist ethos that is common in Anglo-American evanglical Protestantism, and can find its roots in the somewhat atomized nature of Scots-Irish and lowland South culture in the United States. A contrast with this model is that of Mormons, who share values with evangelical Protestants, but whose folkways reflect the more communitarian ethos of New England Yankees and German or Scandinavian peoples. I suspect that the lower divorce rate (and social pathology more generally) among Mormon Americans in comparison to white evangelical Protestants has more to do with the nature of their collective institutions than the individual dispositional nature of believers.

50thversion On the other hand, this viewpoint does not necessarily support the instincts of modern technocratic liberalism. In general technocratic liberals seem to think that many social ills have a small number of causes, and so are tractable through public policy. Often these causes are pinned down on single institutions (e.g., schools), or, a lack of funds. Recently universal pre-school has been all the rage because of its near magical ameliorative properties. But the social science on that is decidedly mixed. I suspect that universal pre-school as a simple institutional fix is far inferior to the rich civic and social matrix which Jane Jacobs described in The Death and Life of Great American Cities. Not only because organically developed social and civic institutions provide services which pre-school can not replace, but also because a society which gives rise to such institutions is by its nature more healthy and exhibits less anomie. In some ways Mao was right that a true solution toward fixing social ills is a “cultural revolution.”

• Category: Science • Tags: Behavior Genetics 
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tnapb4 The “nurture assumption” is basically the idea that parents really, really, matter in affecting variation in individual outcomes in their children. Judith Rich Harris famously wrote a book length critique, The Nurture Assumption: Why Children Turn Out the Way They Do, which was published in 1999. I’ve argued that the Steven Pinker’s The Blank Slate is important in large part because it introduced a broader audience to Harris’ conclusions. Though the pattern that she observes, that most variation in outcomes for individuals does not seem to be accounted for by shared environment, that component that is under parental control, is a robust behavior genetic finding it runs against deep human intuitions. This is one domain where political Left and Right share the same sympathies, though the details differ. Many cultural conservatives in the United States impute to parents an almost alchemical power to shape the nature of their children through inculcation. Similarly, cultural liberals attribute the same sort of power to society broadly construed.

If you’ve been reading me for 13+ years you know all this. As a parent these last four years I’ve had to struggle with the nurture assumption myself. For psychological and social reasons the impulse is strong within us. Recently Brian Boutwell has been doing the Lord’s work, so to speak, in Quillette, reintroducing these ideas to a general audience. Now he and I have co-authored the latest installment, Heritability and why Parents (but not Parenting) Matter. I invite you to check it out!

• Category: Science • Tags: Behavior Genetics 
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51WB8ztO9qL Whenever I talk about The Nurture Assumption there are a minority of angry and peeved comments. Usually they’re not too coherent, but they don’t get me down. The reality is that the basic message of the book is very important to get out to the American public, by which I mean upper to upper middle class Americans (since these are the target of “think pieces”). The reason is that today the “nurture assumption” reigns ascendant, and makes superhuman demands on parents, especially mothers. This explains some of the reaction to a new paper, Does the Amount of Time Mothers Spend With Children or Adolescents Matter? (ungrated). For a representative example, see in The Washington Post, Making time for kids? Study says quality trumps quantity. Quality as in quality of time.

But one thing bothers me about these treatments in the press: the totally confounded nature of causality. Consider:

The one key instance Milkie and her co-authors found where the quantity of time parents spend does indeed matter is during adolescence: The more time a teen spends engaged with their mother, the fewer instances of delinquent behavior. And the more time teens spend with both their parents together in family time, such as during meals, the less likely they are to abuse drugs and alcohol and engage in other risky or illegal behavior. They also achieve higher math scores.

The implication above is that “time engaged with mother” → “less delinquent behavior.” But we don’t know that that’s causal at all. Rather, it could be a correlation between a third factor, term in “prosociality,” and these two variables. More generally if you look for references to genetics in the original paper you won’t find it. It strikes me that one of the reasons that parental investment doesn’t seem to matter so much is that there are many outcomes they just aren’t effecting, because their primary contribution in heritable, with a major secondary contribution to the environmental context in which children grow up (the “non-shared environment”).

High parental investment also isn’t about the children in the proximate sense (though parents sincerely believe that it matters ultimately). Rather, it’s a form of inter-familial status competition. The “best” parents are those who invest the most, and achieve the best outcomes in their offspring.

• Category: Science • Tags: Behavior Genetics 
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Citation: The Fourth Law of Behavior Genetics, Chabris et al.

Figure citation: Marigorta UM, Navarro A (2013) High Trans-ethnic Replicability of GWAS Results Implies Common Causal Variants. PLoS Genet 9(6): e1003566. doi:10.1371/journal.pgen.1003566

The above is a figure from The Fourth Law of Behavior Genetics (ungated), accepted for publication in Current Directions in Psychological Science. It’s an excellent overview of the intersection of behavior genetics and genomics over the past 10 years or so. The full story is outlined in the paper, fleshed out by the copious and informative citations which litter the text. The point of the above figure is to show how robust many inferences from small effect genome-wide associations are. In particular, there is the standard caveat that a variant which is correlated with disease X in population 1 may not be correlated with disease X in population 2. It actually turns out that in most cases they are correlated across populations. Above you see the correlation in effects (odds ratios) between variants and traits between East Asians and Europeans (common variants are also predictive within families).

The Fourth Law of Behavior Genetics makes no sense unless you know the first three laws outlined by Eric Turkheimer:

* First Law. All human behavioral traits are heritable.

* Second Law. The effect of being raised in the same family is smaller than the effect of genes.

* Third Law. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

By heritable you simply mean that some of the variation of the trait in the population is explained by variation in genes in the population (you see it in the standard parent-offspring regression). The second law refers to the fact that on many behavior genetic traits the influence of shared family environment in explaining variation can be surprisingly small. The final law points to the reality that a lot of the variation we see in people in outcomes seems pretty much random. It’s labeled non-shared environment, but we should think of it more as a noise factor. These “laws” are robust regularities which you need to take into account when considering the likelihood of any given result. What is the fourth law? It’s pretty straightforward: “A typical human behavioral trait is associated with very many genetic variants, each of which accounts for a very small percentage of the behavioral variability.” To give a concrete example, it looks like the largest effect common variants for behavioral traits explain about 10% the variance as the largest effect variant for complex disease or morphological traits, on the order of 0.01% as opposed to 0.1%.

That’s a mighty small effect. To make sense of the heritabilities estimated using classical methods that means that genetic variation is partitioned across many many genes, on the order of thousands. This is why methods to ascertain loci of effect utilizing small sample sizes (e.g., candidate gene studies) were bound to fail, because they didn’t have the power to detect true results. Rather, many of the hits were simply noise which got published because of low stringency of statistical significance.

One objection then might be that the missing heritability consists of very low frequency (i.e., far less than the 1% threshold used to define common variants in terms of minor allele frequency) mutations which have a larger effect. The authors claim that the research currently does not support that finding. That implies that high coverage whole genome sequencing at reasonable sample sizes won’t make a big difference. Second, there are the results out of the GCTA framework. I won’t go into the details, though check out the paper in AJHG. It’s a powerful way to explore heritabilities using genomic data across unrelated individuals that’s rapidly converging on the heritabilities estimated from classical behavior genetic methods.

Finally, in a similar vein, Dominance Genetic Variation Contributes Little to the Missing Heritability for Human Complex Traits:

For human complex traits, non-additive genetic variation has been invoked to explain “missing heritability,” but its discovery is often neglected in genome-wide association studies. Here we propose a method of using SNP data to partition and estimate the proportion of phenotypic variance attributed to additive and dominance genetic variation at all SNPs (Math Eq and Math Eq) in unrelated individuals based on an orthogonal model where the estimate of Math Eq is independent of that of Math Eq. With this method, we analyzed 79 quantitative traits in 6,715 unrelated European Americans. The estimate of Math Eq averaged across all the 79 quantitative traits was 0.03, approximately a fifth of that for additive variation (average Math Eq = 0.15). There were a few traits that showed substantial estimates of Math Eq, none of which were replicated in a larger sample of 11,965 individuals. We further performed genome-wide association analyses of the 79 quantitative traits and detected SNPs with genome-wide significant dominance effects only at the ABO locus for factor VIII and von Willebrand factor. All these results suggest that dominance variation at common SNPs explains only a small fraction of phenotypic variation for human complex traits and contributes little to the missing narrow-sense heritability problem.

• Category: Science • Tags: Behavior Genetics, Genomics 
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A happy Finn

A happy Finn

This morning my attention was brought to an interesting piece in The New York Times, The Feel-Good Gene. It marshals an impressive array of scientific disciplines, genetics, biochemistry, and psychiatry. Concurrently Linda Avey on her Facebook page pointed to where you could find your genoptype for the SNP in question in 23andMe . Because it is geared toward a popular audience without scientific training the original article in The New York Times is a bit vague about the allele and SNP code. But Avey seems correct in her inferences, because the piece does cite an article in Nature Communications, ​FAAH genetic variation enhances fronto-amygdala function in mouse and human. So as the article notes the gene is FAAH, but it makes clear that the SNP is Rs324420. If you look up this variant you see that it is associated with many variations in phenotype. The results for the recent paper from last week, cited in the article, indicate that the mutant/derived allele, A, confers a reduction in anxiety in both humans and mice (the gist of the article). In certain contexts because of the reduced anxiety in individuals who carry the A allele they are better at learning, because they more rapidly “update” to conditions where their initial fear response was an overreaction. At this point I will tell you that I am “wild type.” In other words, I carry the ancestral allele, C, and am of homozygous genotype for that allele. In fact both my parents are homozygotes for the C allele. Since this is the majority allele in most populations that is not entirely surprising.

Mutant/derived allele orange

Mutant/derived allele orange

In passing the author of The New York Times piece observes that “roughly 21 percent of Americans of European descent, 14 percent of Han Chinese living in China and 45 percent of Yoruban Nigerians have been found to carry this gene variant.” These data are from the HapMap. According to them 45 percent of the Yoruba Nigerians in the sample carry the A allele, which means that presumably they are less anxious, on average, than the Chinese. Perhaps this aligns with some expectations or stereotypes you might have?

Well, I decided to check a wider range of populations, because it literally takes about 2 minutes. First, I looked in the HGDP browser. You can see that there is wide variation in African populations. The Mbuti Pygmies of Central Africa have a far lower proportion of the A allele than most European groups, in line with a few East Asian groups, as well as Papuans. Across much of Western Eurasia you see many populations at intermediate frequencies, but it looks as if in Europe there is a cline of A from north to south. One can confirm this with the much larger sample sizes of the 1000 Genomes browser. The highest proportion of A, which purports to be associated with reduced anxiety, is found among Finns, at 29 percent. Then there is the British sample at 24 percent. Finally, both the Spanish and Italian (Tuscan) samples return 16 percent. The South Asian groups all exhibit frequencies of A between 15 and 25 percent (at 18 percent for Bangladeshis, it makes sense why my family would be homozygote for C).

download What about the phenotype in question? I’ll skip over the biochemistry, though it isn’t too difficult in terms of pathways. The original article states that “one community-based study of almost 2,100 healthy volunteers found that people with two copies of the mutant gene had roughly half the rate (11 percent) of cannabis dependence than those with one or no mutant gene (26 percent).” That’s not a trivial sample size, but it’s one study. But, it dovetails with the overall thesis, that the biochemical priors of individuals with the AA genotype might allow them to avoid addictions to “abused drugs, like cocaine, opiates and alcohol.” I’m a little confused about this assertion because I looked up the SNPedia page for this variant, and the first major association of an AA genotype is with alcoholism and drug use! Additionally, I did not mention one thing when surveying populations earlier: the groups with the highest frequency of the A allele are Amerindians. This is clear in the HGDP and the 1000 Genomes results.

AA genotype odds ratio

AA genotype odds ratio

The point of this post is not to suggest that variation within the FAAH locus is not relevant to phenotypic differences in individuals or populations. There’s a lot of epidemiological, and now molecular, biochemical, and neurological, evidence that this missense mutation is important in a functional sense. It is likely to make a difference in outcomes. In The New York Times piece the author speculatively suggests that variation at this SNP somehow perpetuates personality heterogeneity in our species, and is a boon to a society. Granted, this doesn’t seem to be true in all cases, as the Mbuti Pygmies and Papuans may lack polymorphism here. But, it is interesting to me that the derived mutation is found at variable frequencies all across the world. There’s probably a evolutionary and biomedical story here to be told about some sort of balancing selection. But, as with many narratives which are fixated upon endophenotypes, the scientific conclusions aren’t quite cut and dried, and rather are still developing, because the endophenotypes themselves are at the end of a long causal chain.

• Category: Science • Tags: Behavior Genetics, FAAH, Genetics 
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cherubs I spent a bit of this morning on a playground with my daughter, and tried really hard not to hover around her, as is in the norm among parents of my socioeconomic status in the United States (this behavior should most certainly be obviated by the fact that this is a “child safe” playground). This always gets me to thinking about variation in child rearing over history and across cultures. There seems to be an instinct to assume there is one true way to raise children, and this tendency is often quite costly in time and mental energy. The New York Times highlights this nicely with an article titled The Only Baby Book You’ll Ever Need, where the author relays the insights from a academic work by an anthropologist, The Anthropology of Childhood: Cherubs, Chattel, Changelings. The basic observation is pretty straightforward, in some cultures very young children are not cossetted, they are either non-persons, or, they are small adults with non-trivial responsibilities. By “some” cultures what you really mean are the vast majority of societies known across human history, including in the recent past the ancestor of developed Western societies. The contrast here is mostly between WEIRD cultures and non-WEIRD cultures.

nurture But there needs to be a bit more precision here, because the behavior that is alluded to in The New York Times refers to the core readership of that periodical, and don’t reflect all Western societies, or even all American social strata. Before my daughter was born my wife read Bringing Up Bébé, which highlights how different French and American parenting wisdom can be. And even within American society there is variation. Much of what is defined as “American” in these comparative studies actually reflect the folkways of upper middle class cosmopolitans, the sort of people who write and read books on parenting (though this segment of the populace is often the leading indicator of social norms more broadly). And even within living memory the parenting wisdom of the American upper middle class has changed a great deal.

So not only does parenting wisdom vary across cultures, it varies within culture (or perhaps more precisely across subcultures, and over time within a culture. But there’s a final piece of the puzzle which is important to note, a fair amount of the variation in outcomes of children is not due to parental choice in any case. More precisely, about ~10 percent of the variation in outcomes of your children on many metrics is due to the choices you make in a distinctive sense as against what other parents do, while ~40 percent is due to variation in genes, and ~50 percent is just unknown (and often referred to as “environmental”, but in a sense that it isn’t accounted for in additive genetic variance; it could be developmental stochasticity, and so still biological). If you read The Blank Slate or Selfish Reasons to Have More Kids you’ll know this, though perhaps the best primer on this topic is Judith Rich Harris’ The Nurture Assumption.

Meanwhile, there are serious social and legal consequences for raising your kids in a way which wouldn’t have been atypical up until the 1980s. The culture can be irrational longer than you can resist….

Addendum: Two points I forgot to bring up. First, it strikes me that the expected number of children you are going to have shapes these mores. The “high investment” strategy probably doesn’t scale well. It is probably harder to cosset kids when you have half a dozen. Second, the behavior genetic work often focuses on variation within a population. So obviously the cultural context might matter, equalizing outcomes across many families. The key isn’t to think that NOTHING you do matters, but the return on the margin in comparison to peer cohorts for extra effort probably is pretty low. That being said, my daughter is starting Kumon this week so she can read early. Less for academic preparation than for the fact that both her parents are readers, so it seems she’ll enjoy herself more if she can read to herself as early as possible.

• Category: Science • Tags: Behavior Genetics, Parenting 
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Diagnosed autism rates, USA

The_Blank_SlateThe Blank Slate is Steven Pinker’s most prominent book. Over the years I have been feeling that it is more and more important to read just to get a sense of how the world works, perhaps because I’m now a parent. Obviously incorrect assumptions about the nature of reality, and human nature, can lead to disastrous consequences (see: Communism). One of the major issues that one can see from the personal perspective is that the blank slate deludes us with the perception that we are more in control than we are as to how the world shakes out. In a previous post about autism and heritability I tried to calm people down, including myself. And, in earlier comments about behavior genetics and heritability I thought it was useful to emphasize that genetics is the one thing you can control, via picking your partner. Many of the outcomes that are due to environment, and they are not trivial, are just not accounted for. We know that something non-genetic has occurred, but we have no idea.

But, there’s another side of the issue, and that is the conclusion that people take from the blank slate model of human behavior, where there has to be a cause, and where it leads people as they flail about for effective choices that make them feel empowered. Recently I was having a conversation with a friend who works in child development, and she mentioned that she knew of a family where all three sons were at some point along the autism spectrum. The two older sons were on the severe end. As someone conscious of genetics it seems highly unlikely that there isn’t a biological reason for why this couple had three children who exhibit tendencies along the spectrum. But here’s the kicker: the mother did not vaccinate her youngest son. Without awareness and acceptance of a likely genetic factor in this instance she attempted to impose the simulacrum of control upon her world by removing one possible environmental causal variant, even if all the research suggests that is not at issue. It’s easy to take a step back when you are not in the specific situation, and coldly evaluate statistics. That’s obviously not going to happen in this case, but, our society’s lack of awareness of the biological parameters which shape outcomes is clear in this particular case.

• Category: Science • Tags: Behavior Genetics 
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Quantitative Genetics

A new study in Psychological Science, Genome-wide scan demonstrates significant linkage for male sexual orientation, is getting breathless coverage in the press. Representative: “A genetic analysis of 409 pairs of gay brothers, including sets of twins, has provided the strongest evidence yet that gay people are born gay.” As a matter of fact I don’t think this is the strongest evidence that people are “born gay.” The study is decent, and better than what has come before, but the authors themselves in the text acknowledge issues of statistical power. These results could be right, but I doubt this is going to end up being a robust signal.* That being said, at some point in the next ten years I’m pretty sure we’ll localize the genes which carry variants which do result in a higher than typical likelihood of an individual exhibiting homosexual orientation. It’s a matter of time, not if. Behavioral genomics was way too optimistic in the interval 2000 to 2010. I suspect we’re starting to become too pessimistic in the interval 2015-2025.


Molecular Genetics

But the bigger point is that we already know homosexuality has a heritable component. We don’t need to know what genes, we just know that related individuals exhibit a propensity for the trait in direct proportion to their relatedness. Heritability is just the proportion of the variation of the trait (e.g., homosexual vs. heterosexual) within the population that can be explained by the variation of the genes in the population. Heritability of homosexuality is modest, but it is there nevertheless, so there is some biological component.** We’ve known this for a long time. A modest linkage study doesn’t really shift the need much at all. It’s asking and exploring somewhat different questions. It assumes heritability, and is looking to uncover its genetic architecture.

Mendelian Genetics

Mendelian Genetics

The problem here is that the public and the press conflate the concrete biophysical instantiation of genes with the abstract concept of the gene. The latter pre-dates the former by about 50 years. For two generations geneticists developed their field without a precise understanding of the biophysical mechanism of inheritance. But that’s because all Mendelian, and evolutionary, genetics requires is that the units of inheritance follow regular laws across the generations. Quantitative genetics, arguably a branch of applied statistics, is even less tied to the concrete unit of genetic transmission in the form of the DNA molecule.

Concrete physical locations of genes as structures in the material world are important data. In a field like biomedicine it has changed the whole game. Genomics as an enterprise wouldn’t really be possible in a practical sense without our understanding of the physical basis of inheritance in DNA. But that doesn’t make DNA necessarily a game change in understanding whether a trait is heritable or not. Rather, it adds detail and specificity to how a trait is heritable. For applied science the “how” is essential. But for basic research it is not the be all and end all.

* Two reasons that I’m skeptical. First, large effects like this often don’t pan out for behavioral traits. Second, I doubt it’s so simple as a common large effect variant because homosexuality almost certainly decreases fitness directly. For a variant to get moderately common with this sort of effect it had to have another outcome which was strongly favored.

** Note that genetics does not include all biological factors. E.g., developmental stochasticity or some early environmental perturbation in utero with lasting consequences.

• Category: Science • Tags: Behavior Genetics, Genetics 
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Credit: Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. "Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness." Personality and Individual Differences 55.2 (2013): 169-174.

Credit: Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. “Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness.” Personality and Individual Differences 55.2 (2013): 169-174.

The New York Times summarizes some new research in behavior and personality, Holding a Mirror to Their Natures: Looking at Twin Personality Through Look-alikes:

As she expected, the unrelated look-alikes showed little similarity in either personality or self-esteem. By contrast, twins — especially identical twins — score similarly on both scales, suggesting that the likeness is largely because of genetics. Her results were published in the journal Personality and Individual Differences.

For a second study, she teamed with a skeptic, Ulrich Ettinger, a psychologist at the University of Bonn in Germany who had heard about the look-alike project during a postdoctorate at the University of Montreal.

“I thought that if two people looked alike, they would have similar personality traits because people would treat them the same,” he said. “For example, I thought men who looked alike and were tall and handsome would probably be extroverts.”

Their analysis was consistent with the findings of Dr. Segal’s first study: Personality traits do not appear to be influenced by the way people are treated because of appearance. Moreover, they found, there appears to be no special bond between look-alikes.

Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. "Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness." Personality and Individual Differences 55.2 (2013): 169-174.

Segal, Nancy L., Jamie L. Graham, and Ulrich Ettinger. “Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness.” Personality and Individual Differences 55.2 (2013): 169-174.

The original study, Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness, is quite modest in scope. You can see the sample sizes are not large in the table to the left. With that said, I think this is adding to a growing body of results that validate the soundness of the original work on twins in behavior genetics. For many reasons this research program has come under sharp critiques over the past 50 years, but it seems to me that the big picture findings NoTwoAlike of modest heritabilities for most behavioral phenotypes is holding up. For a complementary tack I suggest Whole genome approaches to quantitative genetics, which uses different methods to explore some of the same class of
traits. Relying on the body of twin research alone as a foundation might be a shaky basis for conjecture, but now this area is going multi-disciplinary,
allowing for a stool with multiple legs. Of course all it is doing is confirming modest heritabilities for behavioral phenotypes. But one needs to remember that a lot of the environmental component is not amenable to control, whether by parents or society (i.e., it is “non-shared environment”).

God does play dice.

• Category: Science • Tags: Behavior Genetics 
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tnapb4 Like clockwork every few months I feel prompted to write about The Nurture Assumption. In this case it is due to The New York Times reporting that the American Academy of Pediatrics is now recommending that parents start reading to their newborns. As noted in the piece in The New York Times a major reason for this recommendation is the research which shows that higher socioeconomic status families tend to talk a lot more to their offspring than lower socioeconomic status families, and provide them with a richer vocabulary. The assumption is that this head start allows higher socioeconomic status children to outpace their peers cognitively. Naturally they reference Meaningful Differences in the Everyday Experience of Young American Children. This work surveying 42 families was published in 1995, and concluded that children raised in professional households will hear 8 million more words in a year than children raised in a household on welfare.

But that’s old news. There is also a reference to a 2013 study, SES differences in language processing skill and vocabulary are evident at 18 months. The study here looks at 48 individuals. You can see the major result at the top of this post. To me one thing that strikes me are the rather modest correlations. The children in higher socioeconomic circumstances have larger vocabularies, but it’s not an incredibly big difference. There is a huge amount of variation within socioeconomic brackets, just as there is within families. The standard deviation of IQ in groups of siblings is nearly the same as the standard deviation of IQ in the general population. There’s only so much control families and genes have (shared environment + heritable component).

Naturally the first thing that comes to mind is that socioeconomic status and intelligence are not totally uncorrelated, and intelligence is at least somewhat heritable. Smart parents might simply talk more to their children, and those children will tend to be smarter than you would expect by chance. The authors are aware of the behavior genetic literature, but they tend to argue that it can be interpreted in a way which leaves open the possibility for the large effect of shared environment. In general my prior is to be skeptical of this, because the overall body of research suggests that for many behavioral traits the variation within the population which isn’t genetic (on the order of half) is simply unaccounted for.

9780465023240 (1) This doesn’t mean that there aren’t environmental effects which might result in changes in outcome on the margin. But we just don’t know enough about non-genetic component to assume that a silver bullet policy prescription can be formulated out of a few studies. A few years ago Jim Manzi came out with the book Uncontrolled: The Surprising Payoff of Trial-and-Error for Business, Politics, and Society, where he unveiled the term “high causal density.” In other words, there are lots of causes for some effects, and it is difficult to tease apart the variables so as to engineer appropriate responses. This is clear even in the case of the genetically heritable component, which is often polygenic and difficult to assign to any given gene of large effect. And it is also likely in many cases for numerous environmental variables, some of which may simply be stochastic (which can explain differences between identical twins raised together).

Infant with a vocabulary of zero. Parents (one of them me) has never read to him

Infant with a vocabulary of zero. Parents (one of them me) have never read to him.

Unfortunately a major human cognitive bias seems to be the need to think that we can control things, and effect change. This results in the adherence to fads and fashions such as Freudianism and attachment parenting as the years come and go. The single biggest thing you as an expectant parent can do to have a child with a large vocabulary is to select a mate with a large vocabulary. This won’t guarantee anything, because there is going to be lots of variation on individual outcomes, but in a developed world context this is probably the lowest hanging fruit in terms of ‘return on investment.’ Think of it as ‘loading the die.’ That doesn’t address the issue of inequality, which is really what’s bothering people in this particular case, but I strongly suspect that reading to newborns is going to be a waste of everyone’s time here, though it may make people feel as if they are doing something. Young parents have a finite amount of time, and it seems pragmatic for them to starting reading to children when children can actually start understanding the structure of narratives!

• Category: Science • Tags: American Media, Behavior Genetics 
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The above clip of Neil DeGrasse Tyson has been lighting up my social feeds. It’s made Upworthy. Tyson ends by stating that “Before we start talking about genetic differences [between race and gender], you gotta come up with a system where there is equal opportunity, then we can have that conversation.” The major question that immediately comes to mind with these sorts of assertions, which are quite ubiquitous, is how one determines the extent of equal opportunity if one does not have a model for the outcomes of equal opportunity. The reality is that those making such claims have a model of the outcomes, unstated because it is shared by so many. Proportionate representation, because they assume that in fact that there are no innate dispositional differences* between groups. The Left liberal version of Homo economicus. Once this model is in place then lack of proportionate representation can be taken as ipso facto evidence of lack of equal opportunity.** With this model in hand innate dispositional differences would give the same outcomes, but could be taken as evidence of lack of equal opportunity. So ultimately the “lack of interest” in these issues dovetails nicely with priors. If it turned out there were differences between the groups that the model would start to get messier.***

Since the clips such as above are shared by like minded individuals naturally there’s no strong critique. Rather, the assertions are “devastating”to the opposing view, which are almost entirely absent among like-minded individuals. Larry Summers may be a moderately liberal Democrat, but his airing of possible differences between males and females in the early aughts is now grounds for reading him out of polite company from what I can tell. A few years ago I had dinner with Chris Mooney about his contention that overall there is a greater skepticism of science among Republicans/Right than Democrats/Left. I can accede to this point as being possible. It seems unlikely skepticism of science or religion or any other cultural trait would be equally distributed across the ideological spectrum, and in our day and age in the United States natural scientists tend to align with the political Left, and the political Right has a generalized distrust for intellectuals. But I pointed out to Chris that on the modern cultural Left acknowledgement of sex differences seems to still be in bad odor. But a moderate amount of sexual dimorphism seems to be evident in the natural history of our own species, so it isn’t unreasonable to posit some differences. But many now consider it an implausible prior. Chris was skeptical, as he contended that this battle had ended long ago, and a hardcore “blank slate” position has lost. I wish it were so. I had the experience of having an exchange with a prominent science writer with a background in science who would not concede that men, on average, have stronger upper bodies than women. When push comes to shove I doubt that this person would stand by such skepticism, but it illustrates how deep the reflex is if even basic size and strength differences are now subject to interrogation.

The normative roots of skepticism in this domain become clear when one focuses on the one area where Left and Right invert when it comes to the biological basis of human behavior: homosexuality. As a moderately heritable complex trait it seems entirely likely there is a biological basis for homosexuality, at least in part. But the case has not been clinched by a “gay gene,” nor is the trait one which develops in a genetically deterministic fashion like the generation of five fingers on one’s hand. For reasons common to many complex traits it seems unlikely that there will ever be found a singular “gay gene,” and evidence from fields such as psychology and neurobiology do not offer silver bullet models for how homosexuality comes about, because its expression has environmental correlates (for example, same-sex intercourse is practiced in a facultative manner in prison in the Arab world, without being homosexual orientation, so some nuance in terminology is necessary). But the cultural Left, and now the majority of young Americans, can grasp that a complex behavioral trait does not necessarily lend itself to explanatory models as simple as Newtonian physics. The threshold of skepticism of “innate differences” seems to curiously be lower in this case for the Left, and tuned up higher on the social Right.

Motivated reasoning is powerful. This will not be answered by one blog post, or a decades’ worth of research. Because complex traits have genetic architectures which are not easily reducible to a few genes of large effect, “final answers” may be a while in coming (if ever). But the truth is what it is. Even if people in the United States “lack interest” in particular subjects, that is unlikely to stop other nations, whose economies and scientific institutions are still developing, from exploring avenues of research neglected by Americans. Obviously there are no perfectly objective humans, but one convenient fact about ideological bias is that different groups have different blind spots. The future will likely be one of scientific cooperation as a side effect of competition.

Finally, it is always useful for me to outline some of my thoughts by referring to a piece by one of the greatest population geneticists of the 20th century, James F. Crow. He writes in Unequal by nature:
a geneticist’s perspective on human differences

Two populations may have a large overlap and differ only slightly in their means. Still, the most outstanding individuals will tend to come from the population with the higher mean. The implication, I think, is clear: whenever an institution or society singles out individuals who are exceptional or outstanding in some way, racial differences will become more apparent. That fact may be uncomfortable, but there is no way around it.

The fact that racial differences exist does not, of course, explain their origin. The cause of the observed differences may be genetic. But it may also be environmental, the result of diet, or family structure, or schooling, or any number of other possible biological and social factors.

My conclusion, to repeat, is that whenever a society singles out individuals who are outstanding or unusual in any way, the statistical contrast between means and extremes comes to the fore. I think that recognizing this can eventually only help politicians and social policymakers.

The basic model is exceedingly simple. Representation of the tails of a distribution can be much more skewed than small differences in mean values might imply. Let’s give a concrete illustration. Imagine a population at the mean of the height for American males. 70 inches or 5’10). Assuming a standard deviation of 2 inches and a normal distribution 1 out of 770 males will be 76 inches or above (6’4 or greater).**** Now imagine a population where the average height for males is 71 inches. Obviously most of the distribution will overlap. But now 1 out of 161 males is 76 inches or above. For the two populations the overwhelming number of individuals are going to occupy the vast middle ground about the mean. But for particular professions great height might be indispensable, in which case the two populations may have greatly different representations in such fields.

I’m thinking in the above case American basketball. But it is key to remember that basketball requires more than great height. It requires grace and strength as well. In some domains, such as professional sports and the highest echelons of the academy, it seems likely that individuals will exhibit a combination of exceptional traits, not just one, in which case the above argument is further amplified.

None of this is difficult to understand, even if you reject any empirical basis in specific cases. But 10 years of discussing this topic has informed me that this is irrelevant, when people are highly motivated they will refuse to engage in what Ernst Mayr terms “population thinking”. Rather, they will insist on referring to typologies, rather than distributions, even if one asserts that one is discussing distributions. For one, this is comfortable as a mode of analysis for humans. Categories are clear and distinct. Second, it makes for much easier refutation of plainly incorrect categorical assertions. But despite futility some things must be said now and again.

Addendum: There are some asking how one can disentangle environmental and genetic effects. That is a large part of what fields like behavior genetics, and now much of social science, attempt to do. But that being said I have outlined a very simple design enabled by modern genomics, leveraging the imperfect correlation between genomic ancestry and physical appearance.

* These need not be heritable or genetic. So I’m being vague with the terminology.

** A second implicit assumption is a normative understanding of how humans flourish and the set of choices which they should make to self-actualize.

*** It isn’t logically impossible to contend that there are differences between populations/sexes which make proportional representation unlikely, and, that there are social impediments which might amplify or dampen skewed representation in particular fields. The former cases seem self-evident, but what would I put in the latter categories? Clearly throughout the 20th century the representation of Jews, and later Asians in the United States, in areas of higher education have been dampened by quota systems. Similarly, segregation in sports resulted in an over-representation of non-Hispanic whites in many fields in the United States. Once equality of opportunity was allowed (or in cases where it has been) one saw not a decrease, but increase, is representation in the elite levels away from population wide proportions.

**** In reality many quantitative traits exhibit “fat tails,” so there are more individuals at the extremes than one might expect. But that doesn’t alter the qualitative effect.

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The New York Times has a piece up, Raising a Moral Child, which does a run through on the various orthodoxies and heresies about child-rearing and inculcating values floating around the upper middle class Zeitgeist of modern America. There are plenty of references to research and the like. Literature reviews or not, it always helps to know some history, and realize that many ‘orthodox’ opinions seem to be a manner of fashion, not science (in fact, this is clear when you look at cross-cultural mores; France is today different from the USA when it comes to views on how to raise a good child). But there are things I think that are known, and should be reiterated. So, the author states that:

Genetic twin studies suggest that anywhere from a quarter to more than half of our propensity to be giving and caring is inherited. That leaves a lot of room for nurture, and the evidence on how parents raise kind and compassionate children flies in the face of what many of even the most well-intentioned parents do in praising good behavior, responding to bad behavior, and communicating their values.

The-Nurture-Assumption-Harris-Judith-Rich-9780684857077 Two insights from behavior genetics can shed light here. First, shared-environmental effects are often the smallest proportion of the variation in behavior. This is the part which is due to the family home and the parental influence. Second, the proportion of variance explained by shared-environment tends to go down as people get older. So parental influence tends to diminish.

Obviously part of the reason you behave as you do can be put down to genes. Or more precisely genetic dispositions which express themselves. And another portion can be chalked up to what your parents teach you. But a large proportion, in fact in many cases the largest proportion, is accounted for by factors which we don’t have a good grasp of. We don’t know, and term this “non-shared environment.”* In The Nurture Assumption Judith Rich Harris posited that much of non-shared environment was one’s peer group. This is still a speculative hypothesis, but I do think it is part of a broader set of models which emphasize culture and society, and how it shapes your mores and behaviors, as opposed to the nuclear family.

The research cited in the piece shows how modeling by parents or people in positions of authority can affect short-term changes in the behavior of children. I am sure that these effects are real, what I am skeptical about is that these effects maintain themselves in a non-congenial social environment. To illustrate what I am getting at, imagine two children who are given up for adoption, and whose biological parents are alcoholics. Imagine that you know the biological parents are both carrying genes which are strongly correlated with alcoholism. Both these hypothetical children are adopted into conservative white upper middle class families, one in Orange county California, and another in an affluent suburb of Salt Lake City. Both families are socially conservative, and do not tolerate drinking among their children. My prediction is that the child adopted into a Mormon culture which is far less tolerant of individual choice on the issue of alcohol consumption will have lower risks of being an alcoholic simply because the whole landscape of decisions is going to be altered throughout their whole life. An adopted child with a family history of alcoholism is still going to have a higher risk within their population, but the nature of the population is likely to shift the baseline odds.

Contemporary child-rearing advice and literature has a focus on the nuclear family because parents are the ones buying the books, reading the magazines, and attending the workshops. They want to believe that they have control on the outcomes of their offspring decades after they their leave home. Reality is not congenial to this. Parents do have control, but it is far more a case of establishing frameworks through choice in nationality and cultural identification, and loading the die with genetic dispositions.

* This might actually be genetic or more broadly biological; epigenetics, epistasis, and developmental stochasticity.

• Category: Science • Tags: Behavior Genetics 
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Citation: Vinkhuyzen, Anna AE, et al. "Estimation and Partitioning of Heritability in Human Populations Using Whole Genome Analysis Methods." Annual review of genetics 47.1 (2013).

Citation: Vinkhuyzen, Anna AE, et al. “Estimation and Partitioning of Heritability in Human Populations Using Whole Genome Analysis Methods.” Annual review of genetics 47.1 (2013).

The above are some commonly accepted values for the heritabilities of complex traits in the scientific literature. By heritability I mean to refer to the proportion of the variation in the trait within the population which can be explained by variation of genes within the population. The reason I am very precise is that heritability should not be taken to be some sort of obvious correlation statistic. Even though height is highly heritable in modern societies, the average sibling difference is 1.8 inches (4.6 cm). But, heritability is informative when it comes to populations and patterns of variation that we see around us. A highly heritable trait is amenable to selection for a breeder, while a non-heritable trait is not. But just because a trait is highly heritable does not mean that environment does not matter. One can imagine a scenario of “all boats rising” where environment shifts the trait value equally across the population, while all the variation within the population is still due to genes.

140122_XX_fig1.jpg.CROP.promovar-mediumlargeI’m bringing all this up because W. Bradford Wilcox has a new piece in Slate, What’s the most important factor blocking social mobility? Single parents, suggests a new study. The variable what Wilcox is alluding to in the title is illustrated in the figure to the left: the proportion of single parents in the community is very predictive. Importantly he’s arguing for very powerful community level effects. And certainly the correlation is pretty impressive. And knowing the Left’s love affair with the idea of science, he flogs this correlation rather for all that it’s worth:

Throughout his presidency, Barack Obama has stressed his commitment to data-driven decision-making, not ideology. Similarly, progressives like Krugman have stressed their scientific bona fides, as against the “anti-science” right. If progressives like the president and the Nobel laureate are serious about reviving the fortunes of the American Dream in the 21st century in light of the data, this new study suggests they will need to take pages from both left and right playbooks on matters ranging from zoning to education reform. More fundamentally, these new data indicate that any effort to revive opportunity in America must run through two arenas where government has only limited power—civil society and the American family.

The author is a visiting scholar at the Right-leaning American Enterprise Institute, but he does a good job of being evenhanded and not overtly ideological from what I have read. W. Bradford Wilcox seems to be sincerely driven by a commitment to the social issues he writes about so often. He’s also intellectually honest enough to admit that the lead author of the study which reports this stark correlation “has been careful to stress that this research cannot prove causation.”

At this point you know where I’m going with this. Wilcox admits the complexity and confounds at the heart of phenomenon he’s trying to describe. Naturally one aspect he leaves out are the innate dispositions of individuals due to their heritable makeup. More concretely, personalities differ, and those differences have consequences, and those differences partly have a genetic component. I haven’t thought about all the policy implications of this, but I do know that it makes the story that Wilcox and company tell more complicated, and likely alters the nature of the solutions that they might posit (and definitely the effect sizes they might see). Conservatives often accuse Left-liberals of being “social engineers” who neglect the complex interdependencies of organically evolved cultures. The argument is that they presume that they can model cultural outcomes as if they were as predictable as thermodynamics. But modern American conservatives have fallen into a similar trap, with the mantra “the family” “the family” “the family” as a catchall solution to all social ills. As if society is a simple pliable physical process, and the family one of its easy-to-modulate regulatory components.

It is somewhat tedious to get on this high horse over and over, but it needs to be done. Modern Left-liberals certainly won’t do it. While conservatives harp on the family, liberals focus on the economy. Ultimately both parties are missing a part of the picture, but neither is going to challenge the other on their shared lacunae.

• Category: Science • Tags: Behavior Genetics 
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tnapb4 As a parent it is important to me that my daughter grow up in the context of a two-parent monogamous household. Not only do I find this arrangement congenial for a variety of personal reasons, it is also what society is most optimally set up for. But there is a strong class element today in the United States as to the realization of this ideal. While 94 percent of college educated women giving birth are married, 57 percent of women with a high school education or less are unmarried when they have their first child. These striking correlations emphasize to many social conservatives the importance of marriage in shaping individual outcomes.* The lesson being that if you get get married and complete your education you will not be poor. What immediately comes to mind though is that those who do not get married and finish their education are not an arbitrary subset of the population. For example, they are less likely to have a range of personality traits which allow for trading off utility in the short term for gains in the long term. Giving someone a marriage license and keeping them locked in school may not change these underlying habits of mine and behavior. But this attitude toward the causes and dynamics at work in social ills is not limited to ideological conservatives. It is a widespread view informed by common sense observations. Though many individuals from broken homes do very well, on the whole it is clear from anecdotes and social science that this life history adds stress and diminishes life prospects.

Or does it? Over ten years ago Judith Rich Harris published The Nurture Assumption: Why Children Turn Out the Way They Do. Though the basic argument of the book, which draws from peer-reviewed behavior genetic literature, was outlined extensively in The Blank Slate, it has gotten very little broad cultural traction (though it occasionally pops into the public discussion thanks to economists such as Bryan Caplan and Steven Levitt, who see similar patterns as the behavior geneticists). The primary lesson is that main distinctive contribution parents seem to make to the outcomes of their children in a behavioral and social sense is their genetic contribution. This does not mean that behavioral traits are primarily genetic in terms of explaining the variation in outcomes. Rather, it means that the environmental contribution is not something that parents have much direct control over. In The Nurture Assumption the author proposes that the primary environmental causal factor are peer groups. Though this has not been extensively validated to my knowledge, it seems a plausible enough candidate. For example, children tend to speak with the accents and lexicon of their friends, not that of their parents. If upper-class parents from a particular region share linguistic characteristics with their offspring, it has little to do with the direct parental modeling, as opposed to being embedded in a common social milieu.

As the year progresses you will read a great deal in the press about sociological dynamics and how they effect individuals, often for the worse. In response conservatives will point to the importance of individual responsibility and collective norms in enforcing ideal behavior and life outcomes. Liberals will allude to various structural factors which set up people to make wrong choices, and various governmental solutions which might mitigate and even counter-act these forces. What both viewpoints will neglect is that much of the variation in outcomes in individuals, and across social sets, is likely due to heritable differences in personality. In plainer language individual differences matter, much of which is due to genetic differences. To illustrate what I am talking about, consider the robust correlation between children who are abused who abuse then their own offspring when they become parents. A commonsense explanation here is that inappropriate behavior was modeled, and the parents are now recapitulating what they learned. But one immediate issue that comes to mind is that parents who beat their children with no compunction may have a particular personality profile tending toward low empathy and lack of self-control. This personality profile is likely heritable, and passed to their offspring, who naturally exhibit the same characteristics.

The complexity of life outcomes is such that we must be cautious about how we appropriate the weight of a given causal factor on a social, let alone individual, level. When it comes to complex traits with a genetic component how that variation manifests on a social level is strongly conditioned by cultural context. In a society where physical punishment of children is highly normative abuse may not be due to any personality profile at all, because most people are conformist enough that they follow the broader script. Perhaps it is in societies where the norm is changing and not standardized where personal dispositions come most strongly into play as a factor. Similarly, when it comes to a social ideal like marriage obviously cultural headwinds were such that two generations ago no matter your personality profile the expectation of being wedded was so strong that most individuals fell into line. My point is that as you read story after story this year about the impact of various purely social forces in the media, do not neglect the power of genetic variation in many phenomena. It will give you a better and more complete understanding of what’s really going on, which is the point of it all in the end….

Addendum: Long-standing readers may wonder why I’m posting this, since it’s not particularly original. Because every now and then the unoriginal needs to be restated, because it’s actually original to many.

* It is critical to note that lower SES individuals actually value the idea of marriage as much, or more, than higher SES individuals. Rather, they fail to realize their ideal. Often the idealization of marriage manifests with individuals marrying after the birth of their first child, in some haste.

• Category: Science • Tags: Behavior Genetics 
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Have no fear

There has been a lot of attention to Erika Check Hayden’s piece Ethics: Taboo genetics, at least judging by people commenting on my Facebook feed. In some ways this is not an incredibly empirically grounded argument, because the biological basis of complex traits is going to be rather difficult to untangle on a gene-by-gene basis. In other words, this isn’t a clear and present “concern.” The heritability of many behavioral traits has long been known. This is not revolutionary, though for cultural reasons may well educated people are totally surprised when confronted with data that many traits, such as intelligence and personality, have robust heritabilities* (the proportion of trait variation explained by variation in genes across the population). The literature reviewed in The Nurture Assumption makes clear that a surprising proportion of contribution any parents make to their offspring is through their genetic composition, and not their modeled example. You wouldn’t know this if you read someone like Brian Palmer of Slate, who seems to be getting paid to reaffirm the biases of the current age among the smart set (pretty much every single one of his pieces that touch upon genetics is larded with phrases which could have been written by a software program designed to sooth the concerns of the cultural Zeitgeist). But the new genomics is confirming the broad outlines of the findings from behavior genetics. There’s nothing really to see there. The bigger issue of any interest is normative; the values we hold dear as a culture.

For example:

Chabris says that the work can actually contribute to greater social mobility — for instance, by helping to identify preschoolers who could be helped by more intensive early childhood education. “The fact that people in the past interpreted the results in a certain way doesn’t mean that it shouldn’t be studied,” he says. But not everyone buys that potential misuses of the information can be divorced from gathering it. Anthropologist Anne Buchanan at Pennsylvania State University in University Park wrote on the blog The Mermaid’s Tale that rather than being purely academic and detached, such studies are “dangerously immoral”.

Of course John Horgan reiterates his call for race and IQ research to be banned. To some extent this reminds me of Patricia Churchland’s account of being verbally attacked by an anthropologist in an elevator as a “reductionist.” These are matters of morality, and reflect quasi-religious sensibilities. The science is secondary.

But there’s a major problem when you have norms and facts operating at cross-purposes: the facts are ultimately always there, invariant, and true. Banning research is totally a short-term step, because it isn’t as if the United States, with its particular set of values, has a monopoly on research. Patricia Churchland’s work which reduces human consciousness to a totally natural process would not get funded in Saudi Arabia, or by the Vatican, but that’s irrelevant because it will get funded in the Western world. Similarly, the cultural Left taboos which are very strong in Western academia are far weaker in Asia. Assuming that economic development proceeds apace, someone will do the research, and it will be published. If the facts of the world are as you’d always assumed, you have nothing really to fear.

* I think human psychology is complicated enough though that on some level people do understand the importance of genes. Look at who they choose to reproduce with.

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From what people tell me IQ is a social construct which is totally controlled by environmental variables, and so is not of much interest. But curiously the other day when I looked at the hits on this website over the past 3+ years a huge number of highly accessed posts had to do with intelligence and IQ. In any case, seeing as how many readers of this weblog are having, or going to have, children at a relatively advanced age (in an evolutionary sense) I thought this post would be a good public service announcement. Below is a figure from a preprint posted on arXiv, The effect of paternal age on offspring intelligence and personality when controlling for paternal trait level (via Haldane’s Sieve):

I’m assuming that there’s initially an upward slope because more intelligent men tend to reproduce later (you can confirm this by looking at AGEKDBRN and WORDSUM variables in the GSS). Once you control for education and IQ the effect disappears. But there isn’t a downward slope, which you might predict if the hypothesis of increased mutational load was valid. IQ is a high polygenic trait with variation controlled likely by thousands of genes, but one would presume that large effect de novo variants could change that architecture.

As always, more data is welcome.

• Category: Science • Tags: Behavior Genetics, IQ, Psychology 
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Not that dangerous?

The Philadelphia Inquirer has a long piece which reports on the reality that the ‘crack baby epidemic’ of mentally retarded or unstable individuals turned out to be unfounded. The experimental design is as simple as can be: compare individuals of similar socioeconomic background, and track them over their lives. The past generation since the 1980s crack wave has been an unfortunate, yet illuminating, ‘natural experiment.’ The researchers found that contrary to expectations there are basically no statistically significant differences between ‘crack babies’ and control individuals.* This is not a surprising result, as there were hints of this in the child development literature even in the 1990s. The author of the study focused on a sample of lower class black Americans, and noted that despite the lack of statistical differences in outcomes due to exposure to crack in utero, these individuals have been exposed to a lifetime of an underclass milieu, which is likely not conducive to human flourishing. In other words, the reality is much more banal and unsurprising when viewed in a broader light.

But for general social policy it is critical to point out that even as extreme a shock to the system as crack cocaine does not seem to have strongly inimical long term consequences for individuals. Child development, and the cultural Zeitgeist which draws upon the ‘science,’ is notoriously faddish. In the years after World War II Freudianism and Behaviorism came into vogue, perhaps in part as a reaction to the biological bias of earlier theories of development. Today we have ‘attachment parenting’, which again treats the child as if they are a fragile flower, whose every need must be catered to lest their wilt under the harsh conditions of existence (at least the parental expectation of the needs of the child).

This is why books such as The Nurture Assumption are critical in calibrating the rational parent’s expectations. The takeaway is that the individual choices you make as a parent are a lot less important than the individual genes you contribute as a parent. The environmental component does exist, and is substantial (explaining the majority of the variance in outcome for many biobehavioral traits). But it is likely that the component you can control is more of the social and collective input. Buying a house in a community with ‘good schools’ probably is rational. And, it is perhaps important to note that some environmental variation is going to be random, and you cannot account for it through even the most fastidious of social engineering programs (e.g. if it is developmental stochasticity in utero).

Much of the same applies to pregnancy, which is why I am quite looking forward to Emily Oster’s new book Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong?and What You Really Need to Know. Let’s keep pregnancy in perspective: it isn’t cancer, women have been bearing children for as long as women have existed. Unfortunately a minority of difficult pregnancies have resulted in the medicalization of pregnancy writ large. Pregnant American women also live in terror that any congenital defect in their children is due to some environmental input for which they are responsible. This is where I think the thalidomide crisis has resulted in a cultural memory which overwhelms empirically based concerns. Though there will be instances where the causal variable is clear, distinct, and easy to remove from the equation, in most instances when development goes awry it will for all practical purposes be random. This is the unfortunate reality of biological process. But as humans we want there to be causal agency in the world, and all the better if that cause can be removed to return the system to a more acceptable state.

With all this in mind the crack baby epidemic was a case of moral panic rooted in plausible biological concerns. After all, it doesn’t seem crazy on the face of it that bathing a fetus with drugs in utero might have long-term consequences. Not only is the model of causation plausible, but the mothers in this case are eminently culpable, and frankly not particularly sympathetic. When biological plausibility aligns with our moral sensibilities for what is just and right in the world (i.e., women who do drugs while pregnant should not be surprised when their offspring are less than stellar), then you have a potent mix which spreads like memetic wildfire. But just because the meme is appealing does not mean it is true.

* This does not mean that crack might not be correlated with particular problems, but the author of this study seems to suggest that once you remove premature infants from the equation the differences disappear.

• Category: Science • Tags: Behavior Genetics 
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The artist

It’s been about a year and a half since I officially became a father. I put the official qualifier there because I knew I was going to become a father about two years ago, and many of the psychological changes probably began then. My own reflections and lessons are obviously influenced by my own specific situation. I am not the primary caregiver. It would be too pat to say that our family is the typical college educated sort in all its details, but it is not that far from the truth. My daughter, and her parents, have resources, both financial and familial, which are not there for about half of Americans. I obviously can’t speak to the struggles of working class single mothers. And the American class system being what it is I can’t say I know any such women very well beyond the level of tenuous acquaintanceship.

The first reflection I want to admit is that it is one thing to assert the power of hertability in the abstract, and another to see it in the concrete. It is easy enough to do a scatterplot of a quantitative trait like height. But at very young ages of much more salience are mannerisms and other less quantifiable behavioral tics. It was immediately obvious within the first month of her life that my daughter has some of her parents’ idiosyncratic habits. To give an example there is a way I pick my fingers, in particular my thumb, without even thinking about it. I share this trait with my mother. My daughter began to exhibit the same behavior in her sleep when she was less than one month old. Similarly, there are a variety of body movements where she reminds me a great deal of my youngest brother…but that is perhaps more a function of the fact that he is the one with whom I share the most in terms of biomechanical affect.

Probably one thing that helps keep my inferences and pattern matching in context and in check is the fact that I’ve read The Nurture Assumption. The central observation of this book is that only about ~10% of differences between children on behavioral traits seems to be due to unique parenting strategies and tactics. In other words, your choices as a parent don’t matter nearly as much as you think. It turns out that about half the remaining variation is due to the genes you contribute, and the other half is unaccounted for. To many of you this may seem a trivial insight, but it isn’t. Our media is saturated by arguments at the heart of which is the assumption that the role of parents is central to the development of our children. The current fad for attachment parenting is a case in point. All of these cultural currents hook into the reality that as parents you do agonize often about the most minor details of your child’s upbringing, and what effects that might have in the long term. This makes sense to be, as much of life is a positional game. I have no reason to doubt that this wasn’t true in the past, in which case the marginal impact of parenting on the individual level may have been quite significant. 10% might not seem like so much, but that’s the difference between a B+ and an A+!

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But the major problems with this assumption of the centrality of parental behavior and modeling crop up when you assume they are incredibly causal on a broader social level. This article in The Atlantic is typical, The Distinct, Positive Impact of a Good Dad. Before disputing some of the interpretation of the data I want to admit that all things equal I believe it is better to have two parents than just one. The problem is that not all things are equal. If you click to enlarge the infographic you will see that it states that “An asterisk (*) indicates a statistically-significant difference (p < 0.05) indicated between the group and those who scored in the top third of relationship quality with their father, controlling for respondent’s age, race/ethnicity, level of mother’s education, and household income.” There is one control I do not see listed there: genetics.

A stylized example will illustrate the problem as I see it. Imagine a random sample of 18 year old women who become pregnant by their boyfriend. Half of the boyfriends refuse to help support the child or enter into a lasting relationship, while half of them do so. After 10-20 years you tally the outcomes of the offspring, and you see that those whose fathers remained active in their lives had far better life outcomes when measured on broad metrics of social dysfunction such as delinquency. One inference you could make is that the environment fathers provide is essential toward stabilizing the home and allowing their children to flourish. That is the conventional conclusion that is normally made both in public and private. And, that is why you control for facts such as mother’s education and income in the result above.

But if you think about it closely you see a rather obvious assumption in the model: that the genetic dispositions of the men who abandoned and those who did not abandon are the same. The sort of “man” who would abandon the mother of his child and his child is likely to have a disposition which will be passed down toward his children, even in his absence. The main blind spot with the idea that “family values” is a panacea for all of our problems is that proponents often give nurture all the credit, and don’t even consider the possibility of heritable dispositions. Behavior genetic work tends to point to the possibility that in fact these heritable dispositions strongly effect life outcomes. Fathers matter, but for rather diverse reasons. Neither his sperm nor his magical presence explain it all.

And yet please remember that a huge fraction of the variation is not accounted for. It doesn’t seem to be straightforwardly heritable, nor is it due to distinct home environment. Judith Rich Harris in The Nurture Assumption proposed that much of the “non-shared environment” was peer group. A simple illustration of the dynamic has to do with accents. Children usually speak with the accent of their peer cohort, not that of their parents. But the reality is that we still don’t know what this non-shared environmental component of variance is. In fact it could be gene-gene interactions, which won’t get captured by measures of heritability. Or it could be developmental stochasticity. I bring these up to point out that even if less than half of the variance of the trait in the population is due to genes that does not entail that it is particularly amenable to reshaping via social policy. Secondarily, even highly heritable traits, such as height (~80% of the trait variation is due to genetic variation) exhibit only mild correlations when you look across siblings (r ~ 0.50 for height). So lesson two: children are going to vary, and you may not have much control over that variation.

Ultimately what my daughter has taught me as a father intellectually in regards to raising her is that I always have to update my assumptions and beliefs, and allow her to give me input into her own development. I don’t subscribe to any major “school” of parenting, nor do I think there is a one-size-fits-all model which would be appropriate for the majority of children beyond the basics (i.e., feed your children adequately and prepare them for the expectations of society as a whole). But natural and social science does give me broad parameters, setting the horizons of the landscape. And yet the space of possible choices is still enormous. For me my daughter is a sort of personal tachyon, her existence is so absorbing that I have a hard time viscerally recalling when she did not exist. And I wouldn’t have it any other way. But that’s feeling, not analysis. And sometimes that is the point!

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Mozart, born that way, trained that way

A few years ago Malcolm Gladwell made the “10,000 hour rule” famous in his book Outliers. In practice (e.g., discussions with people day to day or on this blog) the rule gets translated into the inference “practice is what matters.” When talking about genetics this often implicitly also entails that “genes don’t matter.” I’m not saying that this is necessarily what Gladwell’s own exposition taken literally would suggest, but ideas have a way of evolving once they’re outside of the pages of a book.

My own response is that this sort of rhetorical device is silly. In domains of virtuosity the intersection of innate talent and conscientiousness are often critical. That’s because for outstanding excellence gains on the extreme margin of performance are critical. There are many born with talent, and those who hone and refine that talent will have an edge over those who do not exhibit the same work ethic. But the converse is that there are those born without talent for whom 10,000 hours of invested effort is lunacy.

A piece in Time reports on follow up research which seems to question the 10,000 hour rule. Reading the article one thing that I am struck by is the fact that scholar whom Gladwell originally relied upon to formulate the rule seems like a environmental maximalist. For example:

Ericsson doesn’t deny that genetic limitations, such as those on height and body size, can constrain expert performance in areas like athletics — and his research has shown this. However, he believes there is no good evidence so far that proves that genetic factors related to intelligence or other brain attributes matter when it comes to less physically-driven pursuits.

Update your priors appropriately when evaluating research. In any case the updated findings suggest that practice time can explain ~1/3 of the variance in outcomes for chess and music. This is obviously not trivial, and an important finding in and of itself. But, it does suggest that there is a lot more going on at these elite levels than simply perseverance.

• Category: Science • Tags: Behavior Genetics, Genetics 
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In 2002 I read The Blank Slate. With all due respect to Steven Pinker one of the most fascinating aspects of this book was actually a review of the work of another psychologist, Judith Richard Harris. Harris’ own views are explicated crisply in The Nurture Assumption. In it she reviews and expands on a major insight from behavior genetics: over the long term parental influence seems to be a relatively marginal predictor in terms of many behavioral traits. To be explicit, one can imagine a personality trait which varies in the population. The variation of genes may explain 40% of the variation of the trait. The variation in parental child-rearing techniques, “shared home environment,” may explain 10% of the variation of the trait. The remaining 50% of the variation may be “non-shared environment.” That basically means we don’t have a definitive explanation of what the 50% remainder is, though Harris posits that this consists to a great extent of peer groups.*

However you quibble with the details of Harris’ line of reasoning, the key takeaway is that people often neglect that parents and offspring share genes when considering the influence parents have upon their children. I think it is important to keep this reality in mind when reading pieces like in The New York Times, The Power of Talking to Your Baby. Basically, higher socioeconomic status parents talk to their infants and toddlers more, resulting in a larger vocabulary and presumably giving their offspring a head start. This is a really big deal, and I’ve started hearing about this nugget of wisdom a lot from friends. Providence, Rhode Island, is even spending $5 million dollars to shrink the “word gap.”

Social environment and enrichment matters. The Providence project is exactly the kind of local experiment that Jim Manzi recommends in Uncontrolled. But one of Manzi’s points is that there is no silver bullet in many social science domains. Rather, there are lots of small incremental angles of improvement. And, it seems likely from the behavior genetic data that there are only going to be limited gains in terms of closing presumed intellectual gaps. A plausible, if unpalatable, possibility is that lower socioeconomic status families where there is little complex vocabulary exposure for children are this way simply because these families are disproportionately less intelligent. Adoption studies suggest that I.Q. can increase, at least up to adolescence, by switching a child from a lower (biological) to a higher socioeconomic status (adoptive). But the gap between the adoptive and biological children is not closed. The “word gap” is not going to magically transform the social landscape, though it may have an influence on the margins.

Finally, I have to also be a killjoy and point out that these early life interventions often have a track record of diminishing returns. I am aware of the Perry Preschool Project, and I hope that that pans out, but looking into it it seems that the hopes of many rest on only a few cases. The reason that early gains are often extinguished is that people mature into unstable environments where their initial dispositions may lead them toward choices which prevent them from flourishing. If we’re serious about intervention in the lives of the lower socioeconomic segments of the population we need to get serious in a Nordic fashion: cradle to grave. It seems to me that these periodic enthusiasms for a particular didactic technique reflect the reality that we’re looking for a magical return-on-investment solution. There may be no such thing.

* I am aware that this component may mask epistatic genetic effects.

• Category: Science • Tags: Behavior Genetics 
Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at"