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.
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.*
Over at National Geographic David Dobbs of Neuron Culture has an eminently readable and engrossing piece up, Restless Genes. I have never really read about ‘allele surfing’ on the wave of demographic expansion in the way that Dobbs’ rendered it. I certainly wouldn’t have been able to produce that sort of spare but informative prose.
On Twitter there was some concern about the focus on DRD4. The issue is a general one in much of behavioral genomics, and I’m not too interested in rehashing the point. But the broader question of heritability of behavior remains. It seems to me that we have some ‘natural experiments’ now. For the past 50 years there have been a series of cross-cultural adoptions from Asia to North America and Europe. If human behavior variation across and within populations is substantially heritable than this might be a good place to start. Rather than focusing on genes, we need to focus on heritability first.
In The New York Times David P. Barash writes about how parasites might influence our behavior. This should not be too shocking an idea to readers of this weblog, I’ve blogged about Toxoplasma gondii before, on which there has been a raft of publications over the past 10 years or so. My main issue is that like much of behavior genomics I wonder about the possibility of any terminus and conclusion to this line of inquiry (as opposed to being fodder for high publicity publications indefinitely). For any given personality trait we know that a small proportion (on the order of 10 percent) of the predicted variation within the population is due to variation in family environment (i.e., the impact of parent-specific choices). Of the remaining fraction it is about evenly split between genetic effects (i.e., the genes you inherit from your parents, and the consequent dispositions) and “other/non-shared environmental effects.”
Trends in Genetics has a review article, The genetics of politics: discovery, challenges, and progress. The main reason I point to these sorts of papers isn’t that I think they’re revolutionary. Usually they aren’t. Rather, the public domain has totally forgotten about this domain of study. Most of the informed and high-toned discussion presumes that almost everything of worthy note is socially constructed. If not, then the counterpoint is a crude caricature of genetic determinism which is refutable in a blink of the eye. It’s as if someone was commissioned to paint R. Daneel Olivaw, and ended up using crayon to sketch out the Frankenstein monster.
For example, in sex differences the public debate veers between evolutionary psychological Leave It To Beaver, pre-scientific cultural traditionalism, and de facto Blank Slatism. On the one hand you have to deal with people who use “scare quotes” around the “highly speculative” “hypothesis” that males have a greater tendency toward inter-personal physical aggression than females (including in the comments of this blog, so spare with lectures about how this is a marginal perspective; I’m pretty sure I talk to people about behavior genetics a lot more than you do, though if not I’d like to hear from you!). Set against this you have an elevation of a particular specific and historically contingent nuclear family structure in the post-World War II West as normative by the laws of biology. Never mind that you need to leave the hearth to gather, and that someone must have been minding the farm when citizen soldiers were away at war. Some aspects of the ideal of American social conservatives may actually be socially constructed and economically contingent, rather than being a consequence of the natural laws of society. And just because something is socially constructed does not mean that it is not good or worth defending. And just because you believe that something is natural does not mean that you think that one should never rein in one’s natural impulses. Is and ought are not the same, and they do have relationships, but they’re complex and need to be teased apart precisely. As it is most discussions deal in rhetorical preening and misrepresentation of one’s interlocutors.
The above figure is from a paper I stumbled upon, Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies:
Virginia Hughes has an important post up at The Last Word on Nothing, What Americans Don’t Get About the Brain’s Critical Period. In it she reiterates just how stupid the “Baby Einstein” culture is. The post is important to me specifically because I have a baby who I would like nudge in the direction of Einstein, but not by spending money on toys which exist mostly to salve the vanity and conscience of adults around her. With all that said, Hughes emphasizes that the key is to focus on children at the other end of the environment spectrum from my awesome one.
So I was prompted by her post to check out the links, as I’ve not explored this literature in a while. First, Variation in neural development as a result of exposure to institutionalization early in childhood compares Romanian orphans who were kept in that nation’s notoriously atrocious orphanages and those who were fostered. The authors assert that the placements of the latter were randomized, and the neurological differences were significant. I doubt this is that surprising to most. Romanian orphanages have rightly become a byword for childhood deprivation.
Most of these stolen children were entrusted to the care of Catholics loyal to the regime. The aim behind this was to rid an entire people of the “Marxist gene,” at least according to the theories of Antonio Vallejo-Nájera, the national psychiatrist of Francoist Spain, that were widespread at the time.
More accurately it should be Marxist meme. But it brings up the question of looking into the correlation between the traits of biological parents and their long-lost children.
Over the past few months more and more articles like this one in the The New York Times are coming out, Two Classes, Divided by ‘I Do’:
Jessica Schairer has so much in common with her boss, Chris Faulkner, that a visitor to the day care center they run might get them confused.
They are both friendly white women from modest Midwestern backgrounds who left for college with conventional hopes of marriage, motherhood and career. They both have children in elementary school. They pass their days in similar ways: juggling toddlers, coaching teachers and swapping small secrets that mark them as friends. They even got tattoos together. Though Ms. Faulkner, as the boss, earns more money, the difference is a gap, not a chasm.
But a friendship that evokes parity by day becomes a study of inequality at night and a testament to the way family structure deepens class divides. Ms. Faulkner is married and living on two paychecks, while Ms. Schairer is raising her children by herself. That gives the Faulkner family a profound advantage in income and nurturing time, and makes their children statistically more likely to finish college, find good jobs and form stable marriages.
The story is set up to illustrate the importance of contingency. Two women with very similar backgrounds, and presumably aptitudes, make two very different decisions early on in their lives, and that sets their life path via the constraints or options that that choice enables. We’ve come a long way from the early 1990s when there was a debate, at least at the higher cultural strata, about the necessary value of marriage. But this part jumped out at me:
They stayed with Ms. Schairer’s brother, [the single mother -Razib] visited SeaWorld and Gatorland, and brought back happy memories. But the trip soon began to seem long ago, more a break from their life than an embodiment of it.
As a father the content of my conversations with friends and acquaintances has changed somewhat. Whereas in my offline life discussions of behavior genetics rarely came up, now they loom large implicitly and explicitly. Though the vast majority of people I interact with have graduate degrees or are pursuing graduate degrees in the life sciences almost none of them are aware of the magnitude of the heritability of most bio-behavioral traits.
For those of you who forgot, heritability is a population wide statistic which assesses the proportion of variation in the population you can attribute to heritable genetic variation. So if heritability is 1.0 all of the variation is due genetic variation; offspring are just a linear combination of their parents. If heritability is ~0.0, then there’s basically no correlation between parents and offspring. Though, as I said, heritability is a population-wide statistic, it can be informative on an individual level. For example, the heritabiilty of height is ~0.90 in the Western world. To give you a sense of the expected height of the offspring of two individuals, just take the average (in sex-controlled standard deviation units) and shift it back toward the mean by 10%. There is going to be a lot of variation around this average. The rule of thumb seems to be that the standard deviation across siblings is roughly similar to the standard deviation within the population (though it seems to be a bit lower, with sibling I.Q. deviations being 2/3 of the magnitude of population-wide deviations).
Below the fold is a table reproduced from the paper Genetic Influence on Human Psychological Traits A Survey. Please do not read the table as a gauge of the “geneticness” of the trait. (whatever that means) Rather, it should give you a rough sense of the “pull” that biological inheritance will have on an individual. Biology may not be destiny, but it is definitely probability.
As a follow-up to my post below, I just wanted to check some recent literature on crime and heritability. I found this, Heritability, Assortative Mating and Gender Differences in Violent Crime: Results from a Total Population Sample Using Twin, Adoption, and Sibling Models:
Research addressing genetic and environmental determinants to antisocial behaviour suggests substantial variability across studies. Likewise, evidence for etiologic gender differences is mixed, and estimates might be biased due to assortative mating. We used longitudinal Swedish total population registers to estimate the heritability of objectively measured violent offending (convictions) in classic twin (N = 36,877 pairs), adoptee-parent (N = 5,068 pairs), adoptee-sibling (N = 10,610 pairs), and sibling designs (N = 1,521,066 pairs). Type and degree of assortative mating were calculated from comparisons between spouses of siblings and half-siblings, and across consecutive spouses. Heritability estimates for the liability of violent offending agreed with previously reported heritability for self-reported antisocial behaviour. While the sibling model yielded estimates similar to the twin model (A ≈ 55%, C ≈ 13%), adoptee-models appeared to underestimate familial effects (A ≈ 20–30%, C ≈ 0%). Assortative mating was moderate to strong (r spouse = 0.4), appeared to result from both phenotypic assortment and social homogamy, but had only minor effect on variance components. Finally, we found significant gender differences in the etiology of violent crime
A = additive genetic variance component
C = shared family environment
This table from the paper shows the influence of study design….
In the comments below Nathaniel Comfort asks:
What I do, as a historian, is take something apparently simple and make it more complicated. I wonder about how your curves, e.g., would be applied in real life. *Specific* couples, *particular* children–individuals, cases, persons, context.
I’m asking things like:
-What would your hypothetical psychopathic lovebirds do with that information?
Comfort is referring to this figure I generated, which shows the potential distribution of outcomes for two individuals who tend toward more psychopathy than the general population. It seems to me that this question is easily answered if simply replace “psychopathy” with “odds for heart disease.” Endophenotypes aren’t magical, they’re just sometimes hard to characterize. But once you get a good grip on them you can make standard quantitative genetic predictions. One of the points I wasn’t clear about in the chart is that I assume that the “trait” being measured is the tendency toward psychopathy as measured by a paper & pencil test in one’s youth. This does not entail that an individual in fact behaves like a psychopath. Rather, it simply implies that they’re odds of behaving like a psychopath as an adult are highly elevated. I can’t find the link, but there was a story (which I blogged) a few years ago about a scientist who was studying the peculiarities of psychopath brain structure…and found out that he himself exhibited the same morphology typical of a psychopath. The point is that changing the odds or loading the die does not entail that an outcome is determined.
For example, imagine that you have a long family history of alcoholism. You marry another person with the same history. This sort of thing is heritable, and you’ve just loaded the die for your children. How can you try and compensate? I can think of one simple strategy: convert to a cohesive religious group which bans alcohol consumption, such as Mormons or Salafi Islam. The key here is that the social group is the environment. One can’t likely change that given any environment one’s children are more likely to be alcoholics, but the basal odds are shifted a great deal if you go from being a Catholic to a Mormon.
Also, as a new parent, one thing that I have realized is that behavior genetic understanding of human nature is very useful, it tells us that “attachment parenting” is pretty much crazy. Really more of costly signalling for upper middle class couples than anything else (though less crazy than the 18th century French middle class craze for country wet-nurses which resulted in incredibly high infant mortality rates). Being raised in a Romanian orphanage fucks you up. Your parents, not so much. The “nature vs. nurture” debates are going to continue indefinitely. But parents are will continue to matter less on a day to day level than they think in relation to the outcomes of their children. You can get to set the ground-rules, but there’s no way you will dictate the game.
A few days ago Nathaniel Comfort pointed me to this post, Genetic determinism round-up. If you are curious go read Comfort’s whole post. I honestly didn’t enjoy it very much, I think I got what he was saying, but there were all sorts of circumlocutions around the overall message. But I agree one one thing in particular: an emphasis on concrete and specific genes for traits is a motif in science journalism that can be very frustrating, and often misleading. Nevertheless, that’s not the only story. I believe our current culture greatly underestimates the power of genetics in shaping broader social patterns.
How can these be reconciled? Do not genes and genetics go together? The resolution is a simple one: when you speak of 1,000 genes, you speak of no genes. You can’t list 1,000 genes in prose, even if you know them. But using standard quantitative and behavior genetic means one can apportion variation in the population of a trait to variation in genes. 1,000 genes added together can be of great effect. The newest findings in genomics are reinforcing assertions of non-trivial heritability of many complex traits, though rendering problematic attributing that heritability to a specific set of genes.
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.
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.
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.
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.