heritability

A week of links

Links this week:

  1. Behavioral Public Choice: The Behavioral Paradox of Government Policy. HT: Ryan Murphy
  2. Happiness and growth.
  3. The genetic component of sex offending.
  4. “[I]is growth mindset the one concept in psychology which throws up gigantic effect sizes and always works? Or did Carol Dweck really, honest-to-goodness, make a pact with the Devil in which she offered her eternal soul in exchange for spectacular study results?”
  5. A new Charles Murray book – By the People: Rebuilding Liberty Without Permission
  6. Evolution continues.
  7. The weird belief that people follow dietary guidelines. A question – to what extent do food manufacturers respond to the guidelines, especially to earn “heart smart” certifications and the like?
  8. Economics melts the brain. One alternative which I’ve often seen is, because the model assumptions simply don’t work, they throw every bit of economics they’ve ever learnt out the window and revert to storytelling.

And if you missed it, my one post this week:

  1. Predicting replication.

And a blast from the past: Why isn’t economics evolutionary?

The patience of economists

Over four years since release of the working paper (and two and half years since I posted about it), Henrik Cronqvist and Stephan Siegel’s paper The Origin of Savings Behavior has been published in the Journal of Political Economy (follow the working paper link for an ungated copy). The abstract is as follows:

 Analyzing the savings behavior of a large sample of identical and fraternal twins, we find that genetic differences explain about 33 percent of the variation in savings propensities across individuals. Individuals are born with a persistent genetic predisposition to a specific savings behavior. Parenting contributes to the variation in savings rates among younger individuals, but its effect decays over time. The environment when growing up (e.g., parents’ wealth) moderates genetic effects. Finally, savings behavior is genetically correlated with income growth, smoking, and obesity, suggesting that the genetic component of savings behavior reflects genetic variation in time preferences or self-control.

As I posted last time, the finding is unsurprising and matches findings from behavioural genetics about other traits. Genes matter, heritability increases with age, family environment has little influence and there is a large non-shared environmental effect.

That it takes so long for economics papers to be published makes me thankful for the practice of releasing working papers. We’ve known of and have been able to talk about this result for several years now. It’s always interesting to see the multiple waves of press and attention as different audiences first become aware of a paper at different stages of its life.

But this does have some perverse effects, particularly across disciplinary boundaries. I recently received a referee report suggesting we had neglected some recent literature. Yet the main omission, a paper published in the Proceedings of the Royal Society B, cites the working paper on which our submission was based. Our working paper has been out long enough for people in fields with a faster track to publication to cite it and be published themselves.

So, if we reference that paper, we create a circular set of citations. I’ve spent plenty of time over the last few years following citation chains that do not ultimately establish the point claimed, but I haven’t ended up back where I started too many times yet.

A week of links

Links this week:

  1. The Lancet’s obesity predictions.
  2. Design things to be difficult. HT: Rory Sutherland
  3. Is there any known safe level of government funding?
  4. Increasing diversity by hiring groups, not individuals.
  5. Plenty of critiques of nudge-style interventions popping up, although they are rarely done well. Here’s another. And what is a nudge?
  6. A perspective on consumer genomics.
  7. Wealth heritability.
  8. Edging toward the right answer.
  9. Why it is so much easier to data crunch sport than economics.

And if you missed them, my posts this week:

  1. Tolstoy, behavioural scientist.
  2. The left and heritability.

Accepting heritability

At Stumbling and Mumbling, Chris Dillow writes:

[M]aybe some lefties do reject the heritability of IQ on ideological grounds. I want to make another point – that there’s no need for them to do so. You can accept that IQ (or ability generally) is heritable and still be a strong egalitarian.

I say this because of a simple principle: luck egalitarianism. This says that inequalities are unjust if they are due to circumstances beyond one’s control. If we grant that ability is inherited, then differences in ability are obviously a matter of luck. Insofar as these give rise to inequalities of income, a luck egalitarian can thus claim they are unjust.

That said, there is a sort of leftie who would be discombobulated by the heritability of ability. I’m thinking of that sort, like Tessa Jowell, who – in their optimism about the malleability of humankind – think that education can significantly reduce inequality.

But that leftism isn’t mine. I agree with Ed Smith that social mobility – even if it could be achieved – is an unattractive ideal. It’s no substitute for a just society.

Peter Singer made a related argument in A Darwinian Left: Politics, Evolution, and Cooperation, suggesting that the left needs to incorporate an updated understanding of the malleability of human nature into its framework – although Singer’s arguments focused on our tendency to cooperate.

Arnold Kling suggests the discombobulation of some on the left comes from the need to maintain a narrative:

In the three-axes model, progressives want to squeeze every issue into an oppressor-oppressed narrative. To suggest that ethnic groups differ in average income for reasons other than oppression would be to weaken that narrative. So even if from a policy perspective a belief in heritability is tolerable, from a narrative perspective a book like The Bell Curve represents a huge threat.

My sense is that this produces a great deal of cognitive dissonance on the left. I have many friends on the left, and I do not know a single one who would instinctively deny the heritability of intelligence. On the other hand, they have been instructed to regard Murray and Herrnstein as vile racists.

My own experience is that plenty of people are willing to argue whether behavioural traits are heritable. I sense Kling’s narrative story is part of the reason, but I also suggest that it comes from a general unwillingness of people to concede any points in a debate. (Does this “bias” have a name – or is this just a manifestation of confirmation bias or a desire to reduce cognitive dissonance?)

Take arguments about climate change. Many libertarians or conservatives fight at every step of the way – the earth is not warming, the warming is not caused by human activity, the warming will be mild, the warming will be beneficial – all this before they get to arguments about the costs and benefits of different policy responses. Yet, whether warming is occurring or harmful would not seem to be a core part of the libertarian philosophy. Debates about heritability have a similar character.

A week of links

Links this week:

  1. The case against early cancer detection. The charts on mammogram and PSA testing effectiveness are just as Gerd Gigerenzer would have us present the statistics.
  2. The case for business experimentation.
  3. Airline inequality.
  4. While arguments continue about the predictive power of genetic testing, entrepreneurs are already using it. HT: Steve Hsu
  5. However, there are still plenty of average ‘gene for’ studies being produced. HT: Tim Frayling

Lazy analysis – inequality edition

Over at WSJ Real Time Economics, Josh Zumbrun turns the following chart into a claim that “the SAT is just another area in American life where economic inequality results in much more than just disparate incomes.”

SAT- Student Affluence Test

But what does the chart actually tell us? In a perfect meritocracy, the smartest students will score the highest. But as intelligence is heritable, the smarter kids will tend to have smarter and higher income patterns, giving us the pattern we see in the chart. In an alternative world where parents pay for results, we end up with the same pattern. So that charts tell us nothing. It’s consistent with both worlds.

I’m not exactly Robinson Crusoe in criticising this article. See also Arnold Kling and James Pethokoukis – although the assortative mating Pethokoukis refers to isn’t necessary to get a graph that looks like this, even though it is almost certainly playing a role.

Having picked on this article, the use of a bivariate analysis (a natural result of using a graph) while ignoring other confounding variables is a disappointingly common feature in the increasingly popular “data journalism”.

A week of links

Links this week:

  1. Plenty of press and interesting articles sparked by Peter Thiel’s new book. First, he has a swipe at business schools. And some great one-liners. But is he wrong about the future?
  2. Another tech-billionaire – Elon Musk wants to put people of Mars. But he doesn’t need one million people to get enough genetic diversity.
  3. Eric Crampton has some great posts this week on public health. First, where should the money be going?  Some thoughts on soda taxes and fat taxes. And drinking when pregnant.
  4. Cameron Murray risks walking onto Steven Landsburg’s lawn.
  5. Rajiv Sethi defends agent based models from Chris House. House tends to overreach when he strolls into the unfamiliar and attacks the heterodox rather than his standard (and also not overly convincing) defense of the orthodox.
  6. Put your laptops away kids.
  7. The missing heritability puzzle is slowing being chipped away. But the genetic post-modernists continue their losing battle.
  8. The heritability of educational attainment reflects many genetically influenced traits, not just intelligence. A Science Daily summary. Plus, emotional intelligence is overrated (HT: Stuart Ritchie). Intelligence is important, and to the extent other traits matter, they are heritable too.
  9. Does evolutionary theory need a rethink? No.
  10. Doctor decision fatigue – more unnecessary antibiotics in the afternoon.

The genetic basis of social mobility

The Son Also RisesIn 2007’s A Farewell to Alms: A Brief Economic History of the World, Gregory Clark argued that the higher fertility of the rich in pre-industrial England sowed the seeds for the Industrial Revolution. As children resemble their parents, the increased number of prudent, productive people made possible the modern economic era.

Part of the controversy underlying Clark’s argument – made stark by Clark in articles and speeches following A Farewell to Alm’s publication – was that he considered there may be a genetic basis to the transmitted traits. The higher fertility of the rich and changing character of the population was natural selection at work.

Clark’s new book The Son Also Rises: Surnames and the History of Social Mobility, also makes a new and unique argument. And like A Farewell to Alms, there is a genetic underlay.

Clark’s primary argument is that across a range of societies and eras – from pre-Industrial to modern England, from pre- to post-revolution China, and across the centuries in the United States, Sweden and India – social mobility is low. The correlation in social status between one generation and the next is around 0.7 to 0.8, meaning we can find the echoes of high status 10 or more generations later. Status does “regress to the mean”, but it does so slowly.

To put this in context, Norman surnames are overrepresented at Cambridge and Oxford today by around 25 per cent, 950 years after the Norman conquest. The descendants of the samurai, who lost any legal privileges in 1871, are today several times overrepresented in high status occupations in Japan. The eighteenth century elite of egalitarian Sweden are still a privileged group.

What makes Clark’s finding particularly striking is that most studies of intergenerational mobility have found lower numbers – often an intergenerational correlation of around 0.2 to 0.4. A correlation of that order would erase the traces of social status in a few generations.

Clark suggests one reason for his finding of lower social mobility is that previous studies measured noise. Suppose status is a result of two components – a fixed factor transmitted between generations, and a part determined by luck. Measuring across a single generation, the luck disguises the underlying correlation. If measured across multiple generations, bad lack in one generation will typically be followed by reversion to the underlying status the next. Status across multiple generations provides a better measure of the persistence of social status and of the effect of the fixed factor transmitted between them.

Clark directly relates this point to the biological concepts of genotype and phenotype. The underlying base social status is the genotype. If you observe someone’s external characteristics, you observe the phenotype, which reflects genotype plus some degree of noise. While this might be seen as an analogy, Clark argues that a genetic explanation is the best explanation of what he observes.

A second reason for the difference between Clark’s results and the previous studies is that most studies of intergenerational transmission of status focus on a single measure of status such as correlation in income between parents and their children. But people often trade off one type of status for another. A political leader or leading academic typically receives income that would barely scrape them into the top one per cent. People take lower pay for more prestigious or interesting jobs. Looking a single measure of status will overestimate the change in status as it cannot capture the trade-offs across different domains.

So how does Clark avoid this problem? Clark’s trick is to use rare surnames – an idea suggested to him by the former New York Times science writer Nicholas Wade – and treat them as large families. By finding rare surnames with high or low status, Clark and a range of colleagues tracked the average status of these surnames across the generations through measures such as relative representation in legal practitioner and medical rolls or lists of the wealthy.

As a rare surname comprises many people, the noise and trade-offs across different types of status is averaged out across the “family”. Surname families have an underlying status genotype that can be tracked more faithfully that the individual phenotypes observed in typical studies.

The body of research Clark presents through the book is impressive, although it is not always the most exhilarating reading. As he works through one society to the next, looking at various measures of status, the story is usually the same. Status is persistent and surprisingly similar across times, countries and different measures of status. One interesting finding presented by Clark is over-representation of Norman surnames in the military – and this is not a finding that can be explained by persistence in status. Clark suggests that 10 generations after the Norman conquest, the descendants of the Norman conquerors still had a taste and facility for organised violence.

Clark’s results suggest that while 100 years of Swedish social democracy may have created a more economically equal society, it is no more mobile. The Scientific Revolution, Enlightenment and Industrial Revolution did little to change social mobility in England, and the persistence of status has been almost unaffected by massive changes in inheritance tax. China’s Cultural Revolution had little effect. And across all these countries, government interventions from universal education to progressive taxation have failed to budge social mobility. As Clark states:

Events that at the time seem crucial, powerful and critical determinants of the fate of societies leave astonishingly little imprint in the objective records of social mobility rates.

That social mobility is low but still occurring is a combination of some interesting factors. First, Clark argues that low mobility is affected by assortative mating. If people mate with people of similar status, their children will better reflect their status. However, assortative mating is not perfect. People do not precisely assort by status. And even if they did, observed status (phenotype) does not perfectly reflect the underlying genotype. Both of these factors mean that high or low status people will tend to partner with people closer to the mean, meaning that their children will similarly be closer to the mean.

One way to preserve a group’s status is to have marital endogamy – people only marry within the group – preventing mistakes in marrying low status genotypes that had good luck. This is observed is the highest status castes in India. High status individuals within that group will regress to the mean of that group, but it is regression to a higher mean than that of the rest of the population. The corollary of this point is that to maximise social mobility, you would encourage marriage across groups and status levels.

The inability to observe your potential partner’s status perfectly suggests that if you want to achieve high status, you should not look not just at your potential partner but also at their relatives. Since luck may have affected your potential partner’s status, you gain more information from the status of their relatives. However, these relatives will not contribute anything to the success of your child – transfers of wealth do not make status more persistent. But the status of relatives provides evidence of the social status underlying your potential mate. There are high rewards to this choice. Through appropriate choice of mates, a lineage can avoid downward mobility forever.

In addition to marital endogamy, another apparent exception to regression to the mean is through the loss of low or high status members from high or low status groups respectively. In Ireland, high status Catholics are more likely to change to become Protestant than Catholics of low status, and low status Protestants tend to drift the other way. The expected regression to the mean of these groups does not occur, although if you track Irish surnames, there is still the typical low level of social mobility. Gypsies likely maintain their low status through similar dynamics.

One of Clark’s obvious in hindsight findings is that the social mobility he describes works both ways. In the same way that regression to the mean is slow, the path to the top or bottom follows a similar process. Increases in status are largely driven by random shuffling of genes and good luck in marrying people of better genotype than phenotype. Rags to riches stories and vice versa are rare for whole groups of surnames. The super rich tend to be children of moderately rich, and the poorest children are the children of the moderately poor. This does not mean that you can predict which families will rise to the top – but you can predict the long and slow process.

So why does Clark feel that genetics must be involved, and not transmission of resources or other advantages that accrue to those with high status? As a start, the genetic story is consistent with the mountain of twin and adoption studies that demonstrate a strong role for genetics and a limited role for family environment.

One of his more interesting arguments is that genetics is required to explain regression to the mean. In modern societies, high status people typically have lower fertility and are able to make much larger investments in each child. If this transfer to children mattered, status should persist or these groups should move even further above the mean.

A weakness with A Farewell to Alms was that Clark did not seem ready to bite the population genetic bullet. The tools of population genetics could have helped Clark nail his points and put to bed many of the criticisms that were made of his work. Since then Clark has spent a lot more time in the company of geneticists, and this is reflected in his arguments. His use of genetic data in interpreting the social mobility in Ashkenazi Jews helped his argument cut through. He still does not use population genetic tools in the way he could, but it seems he is much more prepared to fight on the genetic front.

So what do Clark’s arguments mean for how we should think about inequality or social mobility? Clark points out that a genetic basis to social mobility means that people do not achieve what they do because of family background. Instead, it is their ability, their propensity to work hard, and their resilience to failure that leads to success. We can predict success based on family background, but family background is not the cause.

Clark suggests (and I agree) that world is actually fairer than we believe if there is a genetic basis to social outcomes. Large investments by the upper class are doomed to failure. Do not worry that you cannot afford that expensive preparatory school for your kids. People still need to struggle and put in effort to succeed. Genetics just suggests which people will be most likely to struggle and invest that effort.

Also on the optimistic front, the lower fertility of high status people means that social mobility in the modern world is predominantly upward. Groups tend to move up to fill the space at the top – which is the opposite of the dynamic that existed in pre-Industrial England. (Although I am not convinced that lower fertility of the rich is either a general or a long-term dynamic)

Having slashed through the idea that government policy might promote social mobility, Clark is still relatively progressive in his policy recommendations. As he states, why do we want to multiply the awards to the genetic lottery winners? He prefers a Nordic model where, even though social mobility is low, the gap between those of high and low status is not as large. Clark argues the persistence of status, despite the range of taxation and other measures people have been subject to, suggests reward is not required to stimulate achievement.

I disagree with Clark on this point. Reward is important, but the reward just happens to be status itself. A world with no difference in economic outcomes as opposed to reduced difference could see marked changes in effort. Clark also spends little time discussing the other trade-offs involved in the Nordic model, such as the effect on overall wealth.

Finally, Clark does not ask whether the Nordic countries have lower underlying (genetic) variation in their status. It may be that the Nordic institutions reflect the characteristics of the population, rather than being the cause.

A week of links

Links this week:

  1. The Genetic Genealogist responds to Vox’s tabloid piece on genetic testing.
  2. Attempts to correct false claims often entrench them – the backfire effect. But telling politicians they will be fact checked still reduced their number of lies.
  3. Razib on heritability. Low heritability doesn’t make it easier to shape our children – once we’re above some minimum thresholds, we don’t really know what works.
  4. Tyler Cowen suggests the gender gap will close. I’m not so sure.
  5. Violence in chimps an evolutionary adaptation.
  6. Another study showing low social mobility. HT: Jayman
  7. A great collection of papers on altruism, reciprocity and the glucose model of self control.

Twin studies stand up to the critique, again

The history of twin studies is littered with attempts to discredit them – such as this bit of rubbish. Yet every challenge has been met, with a couple of newish studies knocking off another.

The basic idea of twin studies is that by comparing the similarity of fraternal twins to the similarity of identical twins, you can tease out the influence of their genes. Twin studies tend to find that most behaviours have heritability of at least 0.2 (that is, 20 per cent of the variation is due to variation in genotype), IQ a heritability of over 0.5 and height around 0.8. However, twin studies require an assumption that identical and fraternal twins have equally similar environments, and this is where the critiques begin. If identical twins have a more similar environment, the estimates of heritability may be too high.

The responses, however, are plenty. There are studies of twins reared apart. Adoption studies find similar results. For those who believe that identical twins are treated differently to fraternal twins, there are studies of misidentified twins – where everyone thought they were identical or fraternal, but they were the other. Peter Visscher and friends took advantage of the differences in relatedness between siblings to generate estimates of heritability consistent with twin studies (You are 50% related to your siblings on average, which means you can test how similarity varies with variation in relatedness . For me, that study should have been the final nail in the coffin of any arguments that twin studies hadn’t told us anything).

One critique still floating around is that people who look more similar are treated similarly (although the misidentified twin studies deal with this to a degree). And the New York Times has reported two studies that take on that argument. In the first, Nancy Segal assessed the similarity in personality of 23 pairs of unrelated lookalikes. The similarity – effectively zero. Then in a replication, Segal got a skeptic, Ulrich Ettinger, involved in the project. They found the same result – no resemblance – unlike Ettinger’s expectation that people who looked alike would have similar personalities as people would treat them the same.

As Razib points out, these studies involves a small sample. However, they are yet another piece of evidence pointing in the same direction as all the rest.