I stopped reading much in the area of personality and behavior genetics a few years back. The main reason is I had a really hard time believing there were very good quantitative measures of many of the traits. A secondary issue, though probably nearly as important, is that some friends were making it clear that they strongly suspected that a lot of the studies in the area of behavior genomics were “underpowered” in a statistical sense. These two issues gnawed at me to the point where I pretty much threw my hands up in the air. Mind you, I accept that personality is substantially heritable. But just because something is heritable does not mean that it is obvious that you’ll be able to detect “the gene” implicated in the variation of the trait. I accepted decades of findings in behavior genetics. But it didn’t seem like we were going anywhere beyond it.
Now a new paper out in PNAS uses genomics to shed light on this issue in the same manner as with intelligence or height. The paper is The genetic architecture of economic and political preferences, and it is free to all. The two primaries takeaways are:
Many people say that having children gives you a much better sense of the power of genes in shaping behavior. At least in the abstract sense that is not true in my case. I accept the “conventional wisdom” from behavior genetics that “shared environment” (colloquially, parental input) is relatively marginal in effecting much long term change within reason (i.e., if you don’t beat your kid over the head with a baseball bat and such you don’t have much influence).
To review, on many bio-behavioral traits the different choices parents make seem to account for on the order of ~10 percent of the differences you see in the world out there amongst their (biological) offspring. Of the remainder of the variation about half of it is attributable to variation in genes, and the other half to unaccounted for non-shared environment. In The Nurture Assumption Judith Rich Harris proposes that that last effect can be reduced down to social environment or peer groups. Her line of argument is such that parents are important because of the genes they contribute, and, the environmental milieus which they select for their offspring.
On one level I find this banal to review. If it is not the orthodoxy, this position seems relatively uncontroversial, and the results fall out of the data with minimal manipulation. But as a society such facts have simply not been internalized. In the great framing of “nature vs. nurture,” appealing in its stylistic dichotomy, but not even wrong in its substance, the past few centuries have seen multiple swings between each stylized extreme. That has been a matter of ideology, not science. The popularity of public intellectuals such as Steven Pinker by the turn of the 20th century indicates to me that the high tide of post-World War II nurture-über alles has receded. But the media and popular culture are to some extent lagging indicators. They continue to trumpet correlations between parental choices and offspring outcomes as if there is a causal connection without pausing to consider the possibility both might be being influenced by a confound, genes.
The title says it all, and I yanked it from a paper that is now online (and free). It’s of interest because of its relevance to the future genetic understanding of complex cognitive and behavioral traits. Here’s the abstract:
General intelligence (g) and virtually all other behavioral traits are heritable. Associations between g and specific single-nucleotide polymorphisms (SNPs) in several candidate genes involved in brain function have been reported. We sought to replicate published associations between 12 specific genetic variants and g using three independent, well-characterized, longitudinal datasets of 5571, 1759, and 2441 individuals. Of 32 independent tests across all three datasets, only one was nominally significant at the p ~ .05 level. By contrast, power analyses showed that we should have expected 10–15 significant associations, given reasonable assumptions for genotype effect sizes. As positive controls, we confirmed accepted genetic associations for Alzheimer disease and body mass index, and we used SNP-based relatedness calculations to replicate estimates that about half of the variance in g is accounted for by common genetic variation among individuals. We conclude that different approaches than candidate genes are needed in the molecular genetics of psychology and social science.
A new paper (open access) in The Journal of Economic Perspectives, Molecular Genetics and Economics. The authors introduce the term “genoecomics.” They start out with the proposition that the intersection of genomics and behavioral economics suffers from 1) the study samples are way too small, 2) there’s a publication bias toward false results. It’s a good review of the past decade or so. If the following surprises you, you might gain from reading the paper:
…While genetic variation can statistically account for a moderate to large share of income in contemporary Western societies, this does not mean that it would be infeasible to use redistributive policies or policies that encourage human capital formation to change the distribution of income. Heritability is a
population parameter that depends on both the environmental effects operating in a specifific population at a certain point in time and on the genetic variation in that population. It says little about what would happen to the mean and variance of the trait were the environment to change….
I suspect that the caveats have to be stronger for “endophenotypes”.
A few days ago Kevin Drum put up a post with the title “Being Poor in America Really Sucks”. He linked to a Pew survey which reported that the United states seems to have a stronger correlation between parent-child socioeconomic outcomes than most other nations. The implication here is that social mobility in the United States is lower than in other nations, in contradiction to our national mythology. This seems generally correct, in that I’ve seen this result reported repeatedly for the past decade (I’m sure you could slice and dice the finding to show it wasn’t quite right, but to a first order approximation you’d still have to start with that result before deconstructing it). But the finding itself is not what caught my attention. Drum goes on to say:
But in the United States they do a lot worse. The Pew chart is normalized so that children of middle-educated parents score in the 50th percentile and other children are compared to that standard. In Canada, the least-advantaged kids manage to score at the 37th percentile. In the United States they score at only the 27th percentile.
Now, it’s pretty unlikely that Canadian kids with low-educated parents are genetically unluckier than American kids with low-educated parents. Genes may account for some of the overall difference between rich and poor kids, but not for the difference between Canada and the U.S. That has a lot more to do with how we raise our kids and what kind of attention we give them at early ages. On that score, the United States does wretchedly. We simply don’t give our poorest kids a fair start in life.
Ed Yong has a post up on a behavior genetic publication where the sample size is 23. The researchers report a correlation between a SNP on the OXTR locus and “prosociality.” To make a long story short the sample size suggested to Dr. Daniel MacArthur and Dr. Jospeh Pickrell that this was a spurious correlation. The bigger issue here is that there are functional reasons to assume that some genes are correlated with normal human variation in psychology and behavior, and a robust body of literature that these traits are heritable (trait value is highly predictive across relatives), but, the results associating a particular genetic marker with a given trait are much less robust.
But I immediately realized something interesting: a sample size of 23 may be small, but there is a sample size potentially of thousands! I know my genotype at this SNP from 23andMe. How about some 23andMe customers get together and produce some results, and then get published in PNAS? A sample size of 230 would be easy I think, and you could probably push it much closer to 1,000.
There’s a variable in the GSS, GENEEXPS, which asks if genes play a role in personality. The options are:
- It’s genes which play a major role
- It’s experience which determines personality
First, let’s admit that the premise is stupid. Personality is heritable, but environmental variation also seems to matter. In other words it is noncontroversial to assert that both genes and environment can explain variation in personality (or perhaps more precisely genetic variation can only explain around half the variation for any given trait).
I was curious how this broke down by education and intelligence. To remove demographic confounds I limited the sample to non-Hispanic whites. For intelligence I used WORDSUM, with scores 0-4 being dumb, 5-7 being average, and 8-10 being smart.
Above is the Ngram result for paradigm shift, a ubiquitous descriptive concept which can be quite slippery when applied to contemporary science. For example, every few years there is always a new “revolution” which is going to overturn “Darwinism.” Be it punctuated equilibrium, symbiogenesis, or epigenetics. But over time revolutionary fervor abates, and the orthodoxy remains standing, albeit with modifications and alterations, making it all the more robust.
I thought of this when I saw Andrea Cantor’s comment below in relation to twin studies:
Twin studies underestimate heritability only if you subscribe to the crude notion that the effect of genes is additive, i.e., keeping “environments” the same, the more similar two people are genetically the more alike they will be. This ignores everything we now know about the way genes work.
Genes are not self-activating: they do not turn themselves on and produce traits. Genes do not, in fact, produce anything. Genes are turned on and off by the epigenome in response to environmental inputs. If you are inclined to doubt this, then consider: If all the cells in our body are supposed to contain identical DNA, how do you account for the existence of different tissues and cells types (answer: the epigenome). Twins have been shown to have significantly different epigenomes in the womb. Does this show that twin studies underestimate heritability? Of course not. It shows, rather, that these studies are out of touch with advances in molecular genetics.
You are all committed to a crude, 19th century conception of the relationship between genotype and phenotype. Twin studies are based upon a scientific paradigm that has remained unchanged since the time of Galton. Problem is, recent advances in molecular genetics are bringing about a paradigm shift in the science of genetics.
Twin studies make it seem all so easy: All you need is a large data set that has zygosity status and statistical software and any undergraduate can unravel the biomolecular basis of human behavior.
Would that it were so easy.
I’m still scratching my head over the rather atrocious Brian Palmer piece in Slate, Double Inanity: Twin studies are pretty much useless. It’s of a quality which would make it appropriate for WorldNetDaily. Here are the responses of Jason Collins, Daniel MacArthur, and Alex Tabarrok. The comments at Slate were rather scathing too. I observed over at Genomes Unzipped that many of the assertions in the piece were in the “not even wrong/what does that even mean?” class. Palmer is apparently a freelancer at Slate, and they’re doing a bunch of stories on twins this week. I wonder if they just sent him the assignment with instructions on the slant, and he took it a little too far. Even if it was a polemic it was a shoddy and embarrassing one. My main concern is that many people perceive Slate to be an organ which publishes “smart” and well researched pieces, and they’ll take Palmer’s screed at face value.
The scientific problems with the article are legion. But still: how does something like this get published in a relatively high-end publication? Brian Palmer has editors presumably. If the copy was an undergraduate paper the prose would be relatively polished, but the overall structure of the argument and the naked guilt by association are marks of hurried sloppiness. The attempt to smear twin studies by association with Francis Galton was pathetic and childish. What next, turn against the concept of statistical correlation because Galton introduced it? There has to be more to this story than what we know. Or perhaps the people at Slate just don’t know anything about science.
A few friends have pinged me on this piece in Slate, Double Inanity: Twin studies are pretty much useless. The headline is bold, but the piece is just a sloppy mishmash. It’s really something amenable for a major “fisking,” but I generally don’t like doing that sort of thing, because it doesn’t seem a optimal allocation of time (though I have to note that the author seems to be implicitly using a colloquial form of the concept of heritability, which I think is going to confuse an already naive audience). A lot of the article is taken up with criticisms of political scientist John Alford’s behavior genetic findings on the heritability of ideology. I’ve had personal communication with other researchers in this area who actually are broadly critical of Alford’s methodology, but they’re still strongly invested in using genomics and behavior genetics to explore this issue. In other words, rejecting Alford’s conclusions does not entail that you just reject twin studies, as such.
Above is the distribution of self-reported I.Q.s of the readers of this weblog according to the 2011 survey. I point this out because my friend Steve Hsu will be giving a talk at Google later today. Here are the details:
The Cognitive Genomics Lab at BGI is using this talk to kick off the drive for US participants in our intelligence GWAS. More information at www.cog-genomics.org, including automatic qualifying standards for the study, which are set just above +3 SD. Participants will receive free genotyping and help with interpreting the results. (The functional part of the site should be live after August 18.)
Title: Genetics and Intelligence
Abstract: How do genes affect cognitive ability? I begin with a brief review of psychometric measurements of intelligence, introducing the idea of a “general factor” or IQ score. The main results concern the stability, validity (predictive power), and heritability of adult IQ. Next, I discuss ongoing Genome Wide Association Studies which investigate the genetic basis of intelligence. Due mainly to the rapidly decreasing cost of sequencing, it is likely that within the next 5-10 years we will identify genes which account for a significant fraction of total IQ variation.
We are currently seeking volunteers for a study of high cognitive ability. Participants will receive free genotyping.
From what I recall of my discussion with Steve the aim here is to fish in the extreme tail of the distribution to see if that allows for an easier catchment of I.Q. upward incrementing alleles. 3 standard deviations above the mean I.Q. is about 1 out of 750 individuals or so.
A few people have pointed me to Charles Murray’s comment at The Enterprise Blog, The Debate about Heritability of General Intelligence Radically Narrows, which alludes to the recent finding of genomic confirmation of the behavior genetic heritability measure for intelligence. Murray indicates that this should end the “debate” on the heritability of intelligence as a quantitative trait. As I implied earlier much of this debate had more to do with rhetoric and ideology than reality, in that I doubt many people support a very low heritability measure for intelligence ( < ~0.30) in developed societies when they don’t have strong ideological commitments. These commitments being that social policy can homogenize environments enough that only the genetic components of variation of a trait value will be important in the future, so that heritability values will go from ~0 to ~1.0.
A new paper in Molecular Psychiatry has been reported on extensively in the media, and readers have mentioned it several times in the comments. I read it. It’s titled Genome-wide association studies establish that human intelligence is highly heritable and polygenic. But the fact is that I read this paper last year. Back then it was titled Common SNPs explain a large proportion of the heritability for human height. I kid, but you get the picture. The new paper establishes for intelligence what we already suspected: most of the genetic variation in this heritable trait is accounted for by numerous genes of small effect. You inherit variants of these numerous genes from your two parents, and your own trait value is to a large extent a combination of the parental values. The issue is not if intelligence is heritable, but the extent of that heritability.
A new paper in PLoS Biology is rather like the last person to leave turning the light off. Evolutionary psychology as we understood it in the 1980s and 1990s is over. Darwin in Mind: New Opportunities for Evolutionary Psychology:
None of the aforementioned scientific developments render evolutionary psychology unfeasible; they merely require that EP should change its daily practice. The key concepts of EP have led to a series of widely held assumptions (e.g., that human behaviour is unlikely to be adaptive in modern environments, that cognition is domain-specific, that there is a universal human nature), which with the benefit of hindsight we now know to be questionable. A modern EP would embrace a broader, more open, and multi-disciplinary theoretical framework, drawing on, rather than being isolated from, the full repertoire of knowledge and tools available in adjacent disciplines. Such a field would embrace the challenge of exploring empirically, for instance, to what extent human cognition is domain-general or domain specific, under what circumstances human behaviour is adaptive, how best to explain variation in human behaviour and cognition. The evidence from adjacent disciplines suggests that, if EP can reconsider its basic tenets, it will flourish as a scientific discipline.
Gregory pressed, asking “Is being gay a choice?”
Pawlenty ultimately said, “I defer to the scientists in that regard.”
Again, Gregory pressed: “So you, you think it’s not a choice. … That you are, as Lady Gaga says, you’re born that way.”
Said Pawlenty: “There’s no scientific conclusion that it’s genetic. We don’t know that. So we don’t know to what extent, you know, it’s behavioral, and that’s something that’s been debated by scientists for a long time. But as I understand the science, there’s no current conclusion that it’s genetic.”
Epigenetics is making it “big time,” Slate has a review up of the new book Epigenetics: The Ultimate Mystery of Inheritance. In case you don’t know epigenetics in terms of “what it means/why it matters” holds out the promise to break out of the genes → trait conveyor belt. Instead positing genes → trait → experience → genes, and so forth. Or perhaps more accurately genes → trait × experience → genes. Epigenetics has obviously long been overlooked as a biological phenomenon. But, I think the same could be said for the ubiquity of asexual reproduction and unicellularity! Life science exhibits anthropocentrism. That’s why there’s human genetics, and biological anthropology. My own concern is that epigenetics will give some a license to posit that the old models have been overthrown, when in fact in many cases they have been modified on the margin. Especially at the level of organisms which we’re concerned about; human-scaled eukaryotes. Humans most of all.
The last paragraph in the review highlights the hope, promise, and perils of epigenetics in regards to social relevance:
At The Intersection Chris Mooney points to new research which reiterates that 1) political ideology exhibits some heritability, 2) and, there are associations between political ideology and specific genes. I’ll set #2 aside for now, because this is a classic “more research needed” area at this point. But as I mentioned in the comments the heritability of political ideology is well known and robust. From what I can gather most people assume it’s mediated through personality traits. In the comments Chris asks:
That sounds sensible. What i find amazing is that if the heritability of politics is so robust–and I agree, it would happen via personality–why is this so widely ignored?
There are I think several issues at work. First, many people are not comfortable within imagining that beliefs which they attribute to their conscious rational choice are not only subject to social inculcation, but that may also have an element of genetic disposition. Second, most people have a poor grasp of what heritability implies. Take a look at some of Chris’ commenters. The response is generally in the “not even wrong” class. Finally, what’s the actionable component to this? In other words, what are people going to do with this sort of information?
Update: Stephen Dubner emailed me, and pointed me to this much longer segment which has a lot of Bryan Caplan. So it seems like the omission that I perceived was more of an issue with the production and editing process and constraints of the Marketplace segment than anything else.
I play a lot of podcasts during the day as I go about my business on my iPod shuffle. One of them is Marketplace, which has a regular Freakonomics Radio segment, where Stephen Dubner “freaks” you out with incredible facts and analysis, often with a helping hand from Steven Levitt. With all due respect to Dubner and Levitt, this still has very pre-Lehman feel. Economics has “solved” the workings of the explicit market, so why not move on to other areas which are ripe for conquest by the “logic of life?”
In any case this week’s episode kind of ticked me off just a little. It started off with the observation that college educated women apparently put 22 hours weekly into childcare today, vs. 13 hours in the 1980s. I guess fewer latchkey kids and more “helicopter parents?” Dubner basically indicates that the reasoning behind this is many parents are in a “red queen” arms race to polish the c.v.’s of their children for selective universities. This makes qualitative sense, but can we explain an increase of 9 hours on average for the ~25% of women who are college educated on striving to make sure that their kids have Wesleyan as the safety school?
Let’s put our quantitative “thinking-caps” on “freakonomics” style. ~25% of adults have university degrees. ~80% of these have public university degrees, which are usually not too selective. Some of the ~20% are from not particularly elite religious colleges. So the subset of Americans who graduated from elite universities is actually not too large a number. You can include these as natural aspirants for the best spots for their children. And a proportion of the large remainder, I’d estimate ~90%, who didn’t go to a university which required a great deal of stress and c.v. polishing would certainly strive and hope for better for their kids. But can this explain a 9 hour average rise among tens of millions of women? Doesn’t seem to pass the smell test for me. I suspect there’s a more general norm of shifting toward “high investment parenting” among the college educated cohorts.
In the post below, Moderate marginal value to genomics, I left some things implicit. It turns out that this was an ill-considered decision. In reality my comments were simply more cryptic and opaque than implicit. This is pretty obvious because even those readers who are biologists didn’t seem to catch what I had assumed would be obvious in the thrust of my argument.
The point in the broadest sense is that DNA and genomics are not magical. Genetics existed before either of them. Understanding the physical basis of genetics has certainly been incredibly fruitful, and genomics has altered the playing field in many ways. But there was a broad understanding of genetics before DNA and genomics, both in a Mendelian sense and in the area of biometrics and quantitative genetics. In the earlier post I indicated that the tools for predictions of adult traits due to the effect of genes have been around for a long time: our family history. By this, I mean that a lot of traits of interest are substantially heritable. A great deal of the variation within the population can be explained by variation of genes in the population, as inferred by patterns of correlation between individuals in their traits as a function of genetic relatedness. This is genetics as a branch of applied statistics. It has great “quick & dirty” power, especially in agricultural science.
Let’s look at something simple, height. It’s a continuous trait which is rather concrete. No one argues that “height” is a social construct. In Western societies height is ~80-90% heritable. That means that most of the variation within the population of the trait can be explained by variation in one’s family background. Tall people have tall children, short people have short children, and so forth. Here’s a “toy” scatterplot which shows the relation between mid-parent heights and adult offspring heights (I made up the numbers):