But the big shock here is schizophrenia. As of last time I checked, the leading hypothesis was that schizophrenia genes were just really bad, evolutionary detritus that we hadn’t quite managed to weed out. And although they definitely decrease IQ, they seem to be good in other ways. Not with certainty: the correction for false discovery rate kills a lot of the effect (though this is the question I would have been most interested in before reading these results, so maybe I can ignore that?). But there’s at least a faint signal here.
I’ve actually heard from psychometricians that there is a weird signal in relation to the genetic correlation between schizophrenia and various outcomes which are not all negative. One model for schizophrenia you might have is that it’s totally bad. But, another model might be that it’s “good actually” in small dosages or in some genetic backgrounds, but bad in other cases. The argument can be generalized to many “mental illnesses.”
The issue more broadly is that the genetic architecture of mental/behavioral traits is complex, and often subject to a normal distribution. Is this simply mutation-selection balance? Or is there balancing selection? There is now evidence that markers associated with homosexual behavior boost fertility when present in individuals who are not gay. This could be a simple way that these alleles remain in the population at a given frequency (assume frequency dependence). As we understand the genetics of schizophrenia and autism, and begin to screen embryos, I think these questions will become more relevant.
We investigated the heritability of educational attainment and how it differed between birth cohorts and cultural–geographic regions. A classical twin design was applied to pooled data from 28 cohorts representing 16 countries and including 193,518 twins with information on educational attainment at 25 years of age or older. Genetic factors explained the major part of individual differences in educational attainment (heritability: a2 = 0.43; 0.41–0.44), but also environmental variation shared by co-twins was substantial (c2 = 0.31; 0.30–0.33). The proportions of educational variation explained by genetic and shared environmental factors did not differ between Europe, North America and Australia, and East Asia. When restricted to twins 30 years or older to confirm finalized education, the heritability was higher in the older cohorts born in 1900–1949 (a2 = 0.44; 0.41–0.46) than in the later cohorts born in 1950–1989 (a2 = 0.38; 0.36–0.40), with a corresponding lower influence of common environmental factors (c2 = 0.31; 0.29–0.33 and c2 = 0.34; 0.32–0.36, respectively). In conclusion, both genetic and environmental factors shared by co-twins have an important influence on individual differences in educational attainment. The effect of genetic factors on educational attainment has decreased from the cohorts born before to those born after the 1950s.
One of the stylized facts of behavior genetics that isn’t well known to the public is that “shared environment” doesn’t matter that much. By this, I mean shared home environment. This was the major thesis of Judith Rich Harris’ The Nurture Assumption. So what’s going on with this result? The shared environment does seem to matter for educational attainment!
First, I want to touch on how these sorts of results might be interpreted. On Twitter some have suggested that a low shared environment fraction is promoted by hereditarians to emphasize how we can’t change things in regards to the status quo. My first thought was fear that competitive investment in children does return positive yields, and how much more as a parent will I have to invest???
The point is that a particular empirical result has a lot of different conclusions for a lot of different people. It’s not as predictable as you might think.
But in regards to this result, I asked a friend who is a behavior geneticist, and his response calmed me. Basically educational attainment is an output that naturally has a lot of family inputs. Far more than raw IQ. For example, families may know how the college application process works, and how to write the essay, and which extracurriculars to do. Additionally, it’s pretty obvious difference families emphasize education differently, and this is going to matter for students on the margin. I know many people of the same rough intelligence, the ones who went to college had particular family expectations that differed from those who did not go to college.
If you care about social egalitarianism, I think one takeaway is to enforce mandatory standardized testing to identify students who might be promising, and subsidize university for them. Standardized tests are loaded toward the well-off, but far less than all other measures.
Some of you have been reading me since 2002. Therefore, you’ve seen a lot of changes in my interests (and to a lesser extent, my life…no more cat pictures because my cats died). Whereas today I incessantly flog Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past, in 2002 I would talk about Steven Pinker’s The Blank Slate: The Modern Denial of Human Nature quite a bit. The reason I don’t talk much about The Blank Slate is that some point in the 2000s I realized my future deep interests were going to be in population genetics, rather than behavior genetics and cognitive psychology. If you are not a specialist who doesn’t follow the literature. Who doesn’t “read the supplements”. You’re going to stop gaining anything more from books at a certain point.
Similarly, after I read In Gods We Trust: The Evolutionary Landscape of Religion, I read a lot of books on the cognitive anthropology of religion. Until I didn’t. Now that Harvey Whitehouse has teamed up with Peter Turchin, I suspect I’ll check in on this literature again.
But life comes at you fast. Today I think the broad thesis of The Blank Slate seems so correct, that we are not a “blank slate”, that no one would argue with that. Rather, the implications of that thesis are highly “problematic,” and social and cultural constructionism has really gone much further on the Left operationally than they were in the early 2000s. To give a concrete example, you can admit that sex differences are real and significant, but you have to be very careful in mentioning or highlighting specific instances or cases where they matter.
Moving to a more controversial topic, for a long while I’ve pretty much ignored the genomic study of the normal variation of cognition. The reason is that until recently all the studies were very underpowered to detect much of anything. The sample sizes were too small in relation to the genetic architecture of the trait because of the “Fourth Law of Behavior Genetics.”
As 2018 proceeds I think we can say that we are now in new territory. On Twitter, Steve Hsu seems positively ecstatic over a paper that just came out in PNAS. His blog post, Game Over: Genomic Prediction of Social Mobility summarizes it pretty well, but you should read the open access paper.
Genome-wide association study (GWAS) discoveries about educational attainment have raised questions about the meaning of the genetics of success. These discoveries could offer clues about biological mechanisms or, because children inherit genetics and social class from parents, education-linked genetics could be spurious correlates of socially transmitted advantages. To distinguish between these hypotheses, we studied social mobility in five cohorts from three countries. We found that people with more education-linked genetics were more successful compared with parents and siblings. We also found mothers’ education-linked genetics predicted their children’s attainment over and above the children’s own genetics, indicating an environmentally mediated genetic effect. Findings reject pure social-transmission explanations of education GWAS discoveries. Instead, genetics influences attainment directly through social mobility and indirectly through family environments.
Why does this matter? I’m assuming most of you have seen charts like the ones below, which “prove” how the game is rigged against the poor:
The problem that most behavior geneticists immediately have with these popular analyses, which now suffuse our public culture (e.g., the “representation” argument in academic science often takes as a cartoonish model that all groups will have equal representation in all fields given no discrimination; substantively almost everyone believes this isn’t true in some way, but for the sake of argumentation this is a bullet-proof line of attack which every white male academic is going to retreat away from), is that they ignore genetic confounds. This paper is an attempt to address that. Measure it. Quantify it. Characterize it.
The two most interesting results for me have to do with siblings and mothers. Unsurprisingly siblings who have a higher predicted educational attainment score genetically tend to have higher educational attainments. As you know, siblings vary in relatedness. They vary in the segregation of alleles from their parents. Some siblings are tall. Some are short. This is due to variation in genetics across the pedigree. People within a family are related to each other, but unless you are talking Targaryens they aren’t exactly alike. Similarly, some siblings are smart and some are not so smart, because they’re “born that way.”
We knew that. Soon we’ll understand that genomically I suspect.
Second, we see again the importance of maternal effects and non-transmitted alleles. Mothers who have a higher predicted level of education have children with more education even if those children don’t inherit those alleles.* One natural conclusion here is mothers with a particular disposition shaped by genes are creating particular environments for their children, and those environments let them flourish even if they do not have their mother’s genetic endowments. This actually has “news you can use” implications in life choices people make in relation to their partners.
The study ends on a cautionary note. Residual population substructure can cause issues, correcting which can attenuate or eliminate such subtle and small signals. The sample sizes could always get bigger. And ethnically diverse panels have to come into the picture at some point.
That being said, the abstract leaves a little to be desired:
Delay discounting (DD), the tendency to discount the value of delayed versus current rewards, is elevated in a constellation of diseases and behavioral conditions. We performed a genome-wide association study of DD using 23,127 research participants of European ancestry. The most significantly associated single-nucleotide polymorphism was rs6528024 (P = 2.40 × 10−8), which is located in an intron of the gene GPM6B. We also showed that 12% of the variance in DD was accounted for by genotype and that the genetic signature of DD overlapped with attention-deficit/hyperactivity disorder, schizophrenia, major depression, smoking, personality, cognition and body weight.
First, “Delay discounting (DD)”, is another way to say that you have high time preference. That is, you won’t forgo some gains in the short term for greater gains in the long term. You would really “fail” the marshmallow test.
Though there have been legitimate criticisms of the replicability of the effect size of the marshmallow test, there almost certainly is something to time preference and delayed gratification, and its relationship to the ability of young children to master the marshmallow test. In a macroeconomic sense societies characterized by low time preference can sustain lower interest rates, and lower interest rates have all sorts of stimulative properties on long-term economic growth.
But to be clear, the paper above does not detect a variant SNP, rs6528024, which explains 12% of the variance in DD. Rather, 12% of the variance could be accounted for by SNP-chip variance. That is, one could explain the “missing heritability” using the markers they had. The total heritablity of the trait is quite higher, 46% to 62% proportions are citied in the paper (narrow-sense). This means that of the total variance of the trait about half could be explained by additive genetic variance. Obviously the SNP-chip only captured a small minority of that additive genetic variance.
DD is correlated with a lot of things. There is a positive phenotypic correlation with:
Smoking
Substance abuse
Obesity
ADHD
They observed a positive genetic correlation between the variants associated with DD and:
Smoking
Neuroticism
Depression
And a negative genetic correlation with:
College completion
Years of education
Childhood IQ
Schizophrenia
In relation to the last, schizophrenia and DD are positively correlated phenotypically. That probably means that the underlying genetic causes of schizophrenia and DD are very different.
The patterns of correlations offer up a lot of avenues to speculate. They do a little of it in the paper, but are appropriately cautious. It seems entirely likely that in the near future we’ll be able to characterize a lot of the heriability genomically. When we figure out time preference and intelligence we’ll have come close to answering many of the questions that explain why different people have different life outcomes.
Note: It is no surprise that there is a negative correlation between DD (high time preference) and conscientiousness. Also, the association they found, GPM6B, has pretty clear biological relevance. It’s almost certainly real.
In Quillette Hrishikesh Joshi and Jonny Anomaly* ask Are Liberals Dying Out? Since the piece has been shared a fair amount (judging by my Twitter timeline), I thought I should respond to why I don’t think that is a major concern. Let me jump to their last paragraph:
Nevertheless, despite cultural trends, the best available evidence suggests that political ideology is heritable, and that people with liberal personality traits currently have far fewer children than conservatives. If this trend continues, it is possible that the reproductive choices people are making today will influence the political climate of future generations. Over the long run, conservatives could end up winning the ideological contest with fertility rather than arguments.
First, I don’t think the title reflects the modest contentions of the piece. I beseech the editors of Quillette to not engage in the titular hyperbole so common in the mainstream media!
I agree that political orientation seems heritable. That is clear in books like Born That Way. But heritability expresses itself in an environmental context. If you had a totalitarian government most of the phenotypic variation would disappear. Yes, there would be dissidents, but they’d be freaks. Most humans would conform (no, I don’t think the citizens of Soviet Russia were genetic freaks unable to grasp freedom like Howard Roark). The correlation between religiosity and fertility varies by society as well. The more secular the society, the bigger the gap (though last I checked this was not true in China). In a totally conservative future heritable variation for liberalism could just reemerge.
Second, political orientation exists on a relative plane. If one imagines it as some specific thing, or disposition, one can imagine that in the future the liberal-conservative spectrum would exist, but just be shifted. Quantitative genetics has shown that selection can move the mean many standard deviations. I don’t think this is a strong objection to their overall point, but it gets at the fact that we view liberal-conservative tendencies along a distribution (1980s liberal commentator Jeff Greenfield was widely known for making disparaging comments about gays i the prime of his career; that did not destroy his career as a liberal pundit at that time). Perhaps liberal have already won in an age when most conservatives understand and accept that gay marriage is here to stay.
Third, some of the variation is not heritable. It’s random. In fact around half of it within the population. Some people may just be liberal for stochastic reasons. You aren’t going to get rid of this with selection.
Perhaps most essential in terms of theory: frequency dependence. The dynamics of human interaction and decision making are such that the frequency of liberals declining might have an impact on their fitness. To give a weird example, perhaps an economically post-Malthusian society needs a certain number of sub-replacement liberals who engage in particularly productive work to maintain itself. If society slouched rapidly back toward Malthusianism perhaps everyone would just trudge along at replacement.
The big picture problem is assuming constant directional selection and exhaustion of heritable variation is all well and good when you are selecting for wax-seed oil, but human societies are non-linear systems which are subject to big shocks. They aren’t controlled agricultural genetic experiments.
Finally, let me use an analogous case to make an empirical objection. Many people tell me that the future will be religious due to the same dynamics above. This despite the century long trend toward secularization (parenthetical, God is Back was an ill-timed books, as the United States was shifting toward secularization at that time).
But I want to go back further. France was the first nation to start the demographic transition. In the early 19th century the secular elite was worried about the fertility of devout Roman Catholics, in particular the Poles who were arriving. The secular future they envisioned was threatened. It’s been nearly 200 years since these worries, and in those 200 years France has become more and more secular.
My point with this illustration is that if your theory can not predict the past, it can’t predict the future. At least not robustly. Liberal people will always be with us. So will shy people. And atheists too. They may wax and wane, but human variation persists. On the evolutionary genetic level I think frequency dependent dynamics are such that the fait, in the medium term, of low fitness traits is generally to become oddballs, not extinct. And once they are odd they may become fortunes favorites….
Scott Alexander has a post up that is getting a lot of attention, Non-Cognitive Skills For Educational Attainment Suggest Benefits Of Mental Illness GenesNon-Cognitive Skills For Educational Attainment Suggest Benefits Of Mental Illness Genes. Scott concludes:
