Skip to content

Making fine distinctions in understanding hereditability of attitudes

Tyler Cowen points to Robin Hanson who points to this paper by Olson, Vernon, Harris, and Jang, “The heritability of attitudes: a study of twins”. Robin writes, summarizing the paper,

your differing attitudes on abortion, birth control, immigrants, gender roles, and race are mostly due to your genes, while your attitudes toward education, capitalism and punishment are due to your life experiences.

This interested me for two reasons:

1. The variation in political attitudes is inherently interesting–there is clearly a wide range of acceptable political beliefs in any society, and they can’t simply be explained in terms of individual or group interests. And it’s well known that your party ID is predictable from the party ID of your parents.

2. From a statistical perspective, I’m suspicious of sharp dividing lines such as in Robin’s quote (A,B,C are mostly due to genes, X,Y,Z are mostly due to life experiences). In my experience, data don’t usually separate things so clearly, but people can get confused by using statistical significance as an arbitrary criterion.

I’ll give the abstract of the Olson et al. paper, then my thoughts. Here’s the abstract:

The genetic basis of individual differences in attitudes was examined in a survey of 195 pairs of monozygotic twins and 141 pairs of same-sex dizygotic twins. A principal components analysis of the 30 attitude items in the survey identified 9 attitude factors, of which 6 yielded significant heritability coefficients. Nonshared environmental factors accounted for the most variance in the attitude factors. Possible mediators of attitude heritability were also assessed, including personality traits, physical characteristics, and academic achievement. Analyses showed that several of these possible mediators correlated at a genetic level with the heritable attitude factors, suggesting that the heritability of the mediator variables might account for part of the heritable components of some attitudes. There was also some evidence that highly heritable attitudes were psychologically “stronger” than less heritable attitudes.

My thoughts:

1. I love psychology papers (for example, here and here), but they typically have such dry abstracts, and the above is no exception. Nowhere is it stated which attitudes are more hereditable and which are less so!

2. I can’t figure out the ordering of the varaibles in the tables. I usually look to the tables and graphs to try to figure out what’s going on, but there’s are so many numbers here with no apparent structure that it’s hard for me to follow. (Just in case this wasn’t clear by now: I’m no expert in genetics and certainly don’t have an intuitive feeling for a correlation of .62, for example, in this context.)

3. Based on the caption to Table 5, I think the correlations reported at zero are actually just not statistically significant. So Robin might be overinterpreting the differences in his quote above (since, as we know, the difference between significance and non-significance is not necessarily itself statistically significant).

4. I have nothing against the factor analyses, but I’d probably start by trying to understand the correlations in the individual survey responses. If I wanted to study this further (and I think I do), I’d probably start by expressing the information in Tables 1 and 2 graphically. The authors seem to be hung up on choosing the best fitting model for each of the survey responses, but these best-fits are probably pretty noisy. A clearer pattern would perhaps appear from some graphs.

In summary, I’m certainly not being critical of the paper of Olson et al. (or, for that matter, of Robin Hansen in pointing it out to us). A key point of publishing research in journals, after all, is to put out the ideas for others to follow further.


  1. Robin Hanson says:

    I'm happy to be corrected. I interpreted the .62, .55, and .00 in the tables as best estimates of the fraction of variance due to genes, and I tried to concisely summarize in those terms. Is there a better way?

    P.S. the name is "Hanson" with an "o."

  2. Corey says:

    your differing attitudes on abortion, birth control, immigrants, gender roles, and race are mostly due to your genes, while your attitudes toward education, capitalism and punishment are due to your life experiences.

    An instant crappy evolutionary psychology suggests itself to me: attitudes about abortion, birth control, and gender roles are all downstream of one's opinions about sex, and attitudes about race and immigration are both downstream of one's tribal inclinations. Whatever genetic bases might exist for attitudes about sex and tribal affiliation, they have been around long enough for evolution to have affected them. Education, capitalism, and punishment seem to be somewhat higher level concepts, and education (as it is currently thought of) and capitalism in particular have not been on the scene for long at all in evolutionary timescales.

    This sort of post hoc reasoning is surely suspect, but it does lead to a simplistic? interesting?… testable prediction: a genetic basis will only be found for attitudes about issues that have been of widespread concern over evolutionary timescales.

  3. Gregor says:

    That is the meaning of heritability

  4. Andrew says:


    I think the best way to summarize is, first, via a graph showing in one place the raw estimates for all the survey response; second, ultimately a multilevel model that would lead to more efficient estimates for each item. Another complication arises because they're doing some sort of factor analysis. But I don't know exactly how I'd do it in this example, since I have no experience with heritability coefficients. So I have no easy answers…but it's something that I hope to look into at some point.

    P.S. Sorry on the misspelling. The trouble is that I know two (unrelated) statisticians named Hansen.

  5. Thom says:

    I see two main problems in the interpretation. One is related to the meaning of heritability (which is not interpretable as the proportion of x due to genes). Genes and environment are correlated. Religion, gender, race are particularly clear examples of this. If your grandparents came from Sicily you'll have different genes than your neighbours whose grandparents came from Norway. You'll also probably be a different religion. You'll probably also have different attitudes to abortion.

    The second problem is that attitudes are notoriously changeable. I find it therefore hard to think that genetic factors are really that important. More plausibly heritability for some attitudes is larger because environmental variance is lower – perhaps because we're exposed to fewer environmental sources of attitude-change. (This relates back to the first point because heritability is expressed as a proportion of total variation).