The post title is a bit tongue in cheek after I suffered a case of foot in mouth yesterday. I had the pleasure of presenting to some behavioural ecologists at the University of Zurich and was advocating for more “evolutionary biology imperialism” in economics. In the way that economists charge out of their field and seek to spread wisdom on everything, I want to see more evolutionary biologists doing the same and giving their perspectives on economics.
In the question session, we were discussing the heritability of fertility and which traits might influence this. In the back and forth, I stated (roughly) that if a woman in the 1970s adopted feminist beliefs, decided to focus on work and not have any children, her genes and any associated predispositions had now effectively exited the gene pool. While a wiser head might not have referred to feminism in the first place (it certainly didn’t help my case – it doesn’t matter what the particular beliefs are if they are heritable and affect fertility), I gave a brief justification on the grounds that political persuasion is heritable. In the aftermath, I thought I should re-read the article that I had in my mind – hence this post.
The article was by John Alford and colleagues and was published in the American Political Science Review. They analysed the heritability of political attitudes using the results of twin studies, and found that political attitudes had a genetic basis (heritability being the proportion of the variance in attitudes attributable to genetic variation). Attitudes are measured by a test that involves exposing the subject to a phrase with political connotations and asking for a response of agree, disagree or uncertain. Correlation between twins is then measured.
Alford and his colleagues found that the political attitudes of the identical twins were more similar than those of fraternal twins. Across the 28 political attitudes surveyed, the measured heritability ranged from 0.19 to 0.41, with an average of 0.32. Returning to my statement from yesterday, attitudes that might be (crudely) related to feminism include women’s liberation, with a heritability of 0.33, divorce (0.26) and abortion (0.25). The results are summarised in the following table.
Alford and colleagues then constructed an index of “conservatism” for each twin, with an agree or disagree to an issue giving a person a +1 or -1. Scores ranged from +26 to -26 (no-one was uniformly liberal or conservative across every item). For this index, the authors estimated heritability at 0.43, higher than for any individual item. This is not surprising as each issue is more subject to noise and idiosyncratic factors than overall political leanings. The heritability is even higher when the authors controlled for the correlation between parents (i.e. assuming people pair with people more like themselves), with the heritability estimate increasing to 0.53.
One interesting result was that political party affiliation has a lower level of heritability. The authors estimated it at 0.14, with shared and unshared environment the main factors that influence political affiliation. This suggests that parents and peers have a strong influence on which team someone joins, but less of an effect on what their position or overall leanings actually are.
To show that this was not just a United States phenomenon at a particular time, the authors compared the results to some Australian data. The results were similar. On my feminism slant, one of the Australian measures was attitudes to “working mothers”, which had a heritability of 0.27.
Alford and his colleagues closed with a note that heritability is a measure in a particular environment and that if the environment changes, so will the heritability. However, they note a number of implications of their findings for politics. First, they suggest that attitudes with a heritable basis will be more resistant to change. They will also be much harder to manipulate, whether by parents or political players. As evidence of this, the authors note that conservative politics from centuries ago reflects today’s conservative attitudes.
They also stated that a genetic basis to political attitudes means that we are likely to see broad but distinct political phenotypes. While they note that if one political leaning is more adaptive the people holding it should come to numerically dominate the other group, they prefer an explanation in which variation in political belief is adaptive.
For variation to be adaptive, this would require that a person’s fitness would (on average) increase as the prevalence of those who hold similar attitudes decreases. While that is a possibility, I am not sure what would be causing it, and as I wrote yesterday, there may be benefits to fitting in with a group. There is some evidence of positive selection for religiosity, but that would seem to be due to specific characteristics of the religion and not due to its prevalence.
Turning back to the issue I opened the post with, I would suggest that the political attitudes encapsulated under the banner “feminism” would have a heritable component. To the extent those beliefs lowered fertility, the genes associated with those traits would reduce in frequency. However, I am not aware of any empirical data on this. There is no shortage of people drawing the obvious implications in the literature, but has anyone actually done the numbers?