Complexity and Social Networks Blog

There was an interesting paper recently published in the American Political Science Review by Alford et al. that received a lot of attention, which asserted that political orientations have a major genetic component. This paper was done well, by behavioral genetic research standards, I think, a standard analysis of "concordance rates" of identical vs fraternal twins. I do want to pick at one important premise, which is that the strong correlation of political attitudes of identical (monozygotic) twins as compared to fraternal (dizygotic) twins is not due to greater communication and thus social influence between identical twins. Such an assertion is plausible, in that similarity typically predicts communication (homophily)—in fact, this is one of the most robust patterns in social network analysis. I would guess that identical twins see themselves as more similar than fraternal twins do (political orientations aside), and thus talk more. Note that I am unfamiliar with any research that actually demonstrates this (please comment if you are).

The authors do directly tackle this point (see p. 155), but, at first glance, at least, it is a weak reed they rest their assertion on, which is a paper by Martin et al. in 1986. This paper also examines whether identical twins have more similar attitudes than fraternal twins, based on UK and Australian twin sets, producing similar results. Frequency of communication between twins is not the primary focus of their paper. They devote all of two sentences to this issue (excerpt below):

…it is alleged that monozygotic twins see each other more frequently than dizygotic twins and that this greater frequency of contact is reflected in greater monozygotic similarity in attitudes. Since the correlation between reported frequency of contact and absolute intrapair difference in conservatism scores is -0.08 in female and -0.14 in male twin pairs in the Australian sample, any such effect must be trivial, even if the cause of such covariation is in the direction asserted.

As I see it, there are a few problems with this quick disposal of the issue:

(1) There is no explanation of how frequency is measured, so we cannot assess its validity. Further, timing of communication might matter quite a bit—one would guess that frequency of communication in late adolescence and early adulthood would matter a lot more in the formation of political attitudes than later (or earlier) in life. If they simply asked “how often do you talk with your twin,� the study, from a political socialization point of view, is aggregating a lot of apples and oranges.

(2) There is no effort to directly evaluate whether frequency even partially mediates the observed correlation differences between twin types. These are especially problems in view of the likely noisiness in both the political attitudinal and social interaction items. That is, they may be aggregating messy apples and oranges.

In short, this seems like a pretty weak falsification of the hypothesis that identical twins talk more than fraternal twins, and become more similar in political orientations because they talk, rather than being “inherently� similar due to genetic predispositions.

References:

John Alford, Carolyn Funk, and John R. Hibbing“Are Political Orientations Genetically Transmitted?� APSR (May 2005).
See http://www.apsanet.org/imgtest/GeneticsAPSR0505.pdf

Martin, N. G., L. J. Eaves, A. C. Heath, R. Jardine, L. M. Feingold, and H. J. Eysenck. 1986. “Transmission of Social Attitudes.� Proceedings of the National Academy of Sciences 15 (June): 4364–68.
See http://www.pnas.org/cgi/reprint/83/12/4364.