Biology and political orientation
A 2011 study by cognitive neuroscientist Ryota Kanai's group at University College London published in Current Biology, found a correlation between differences in political views and differences in brain structures in a convenience sample of students from University College London. The researchers performed MRI scans on the brains of 90 volunteer students who had indicated their political orientation on a five-point scale ranging from 'very liberal' to 'very conservative'. Students who reported more 'conservative' political views tended to have larger amygdalae, a structure in the temporal lobes that performs a primary role in the processing and memory of emotions. On the other hand, more 'liberal' students tended to have a larger volume of grey matter in the anterior cingulate cortex, a structure of the brain associated with monitoring uncertainty and handling conflicting information. The authors concluded that, "Although our data do not determine whether these regions play a causal role in the formation of political attitudes, they converge with previous work to suggest a possible link between brain structure and psychological mechanisms that mediate political attitudes." In an interview with LiveScience, Ryota Kanai said, "It's very unlikely that actual political orientation is directly encoded in these brain regions", and that, "more work is needed to determine how these brain structures mediate the formation of political attitude."
A study by scientists at New York University and the University of California, Los Angeles, found differences in how self-described liberal and conservative research participants responded to changes in patterns. Participants were asked to tap a keyboard when the letter "M" appeared on a computer monitor and to refrain from tapping when they saw a "W." The letter "M" appeared four times more frequently than "W," conditioning participants to press the keyboard on almost every trial. Liberal participants made fewer mistakes than conservatives when they saw the rare "W," indicating to the researchers that these participants were better able to accept changes or conflicts in established patterns. The participants were also wired to an electroencephalograph that recorded activity in their anterior cingulate cortex, the part of the brain that detects conflicts between a habitual tendency and a more appropriate response. Liberals were significantly more likely than conservatives to show activity in the brain circuits that deal with conflicts during the experiment, and this correlated with their greater accuracy in the test. The lead author of the study, David Amodio, warned against concluding that a particular political orientation is superior. "The tendency of conservatives to block distracting information could be a good thing depending on the situation," he said.
In an fMRI study published in Social Neuroscience, three different patterns of brain activation were found to correlate with individualism, conservatism, and radicalism. In general, fMRI responses in several portions of the brain have been linked to viewing of the faces of well-known politicians. Others[who?] believe that determining political affiliation from fMRI data is overreaching.
Heritability compares differences in genetic factors in individuals to the total variance of observable characteristics ("phenotypes") in a population, to determine the heritability coefficient. Factors including genetics, environment and random chance can all contribute to the variation in individuals' phenotypes.
The use of twin studies assumes the elimination of non-genetic differences by finding the statistical differences between monozygotic (identical) twins, which have almost the same genes, and dizygotic (fraternal) twins. The similarity of the environment in which twins are reared has been questioned.
A 2005 twin study examined the attitudes regarding 28 different political issues such as capitalism, unions, X-rated movies, abortion, school prayer, divorce, property taxes, and the draft. Twins were asked if they agreed or disagreed or were uncertain about each issue. Genetic factors accounted for 53% of the variance of an overall score. However, self-identification as Republican and Democrat had a much lower heritability of 14%.
Jost et al. wrote in a 2011 review that "Many studies involving quite diverse samples and methods suggest that political and religious views reﬂect a reasonably strong genetic basis, but this does not mean that ideological proclivities are unaffected by personal experiences or environmental factors."
Gene associations studies
"A Genome-Wide Analysis of Liberal and Conservative Political Attitudes" by Peter K. Hatemi et al. traces DNA research involving 13,000 subjects. The study identifies several genes potentially connected with political ideology.
Physiology and behavior
Persons with right-wing views had greater skin conductance response, indicating greater sympathetic nervous system response, to threatening images than those with left-wing views in one study. There was no difference for positive or neutral images. Holding right-wing views was also associated with a stronger startle reflex as measured by strength of eyeblink in response to unexpected noise. A study of subjects' reported level of disgust linked to various scenarios showed that people who scored highly on the "disgust sensitivity" scale held more politically conservative views. 
From an evolutionary psychology perspective, conflicts regarding redistribution of wealth may have been a recurrent issue in the ancestral environment. Humans may therefore have developed psychological mechanisms for judging their chance of succeeding in such conflicts which will affect their political views. For males, physical strength may have been an important factor in deciding the outcome of such conflicts. Therefore, a prediction is that males having high physical strength and low socioeconomic stratum (SES) will support redistribution while males having both high SES and high physical strength will oppose redistribution. Cross-cultural research found this to be the case. For females, their physical strength had no influence on their political views which was as expected since females rarely have physical strength above that of the average male. A study on political attitudes among Hollywood actors found that, while the actors were generally leftist, male actors with great physical strength were more likely to support the Republican stance on foreign issues and foreign military interventions.
An alternative evolutionary explanation for political diversity is that it is a polymorphism, like those of gender and blood type, resulting from frequency-dependent selection. Tim Dean has suggested that we live in such a moral ecosystem whereby the viability of any existing moral approach would be diminished by the destruction of all alternative approaches (e.g. political balance promotes survival of the human species).
An editorial for Salon criticized the notion of neurologically determined orientation, saying that it makes people "closed-minded" about others' political views. It argued that biologically deterministic views date back to Thomas Jefferson who erroneously thought the Federalists were more accepting of authority because of "languid [nerve] fibrers".
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- R. Kanai et al. (2011-04-05). "Political Orientations Are Correlated with Brain Structure in Young Adults". Curr Biol 21 (8): 677–80. doi:10.1016/j.cub.2011.03.017. PMC 3092984. PMID 21474316.
- Liberal vs. Conservative: Does the Difference Lie in the Brain? – TIME Healthland
- "Politics on the Brain: Scans Show Whether You Lean Left or Right". LiveScience. Retrieved September 25, 2012.
- Kattalia, Kathryn (April 8, 2011). "The liberal brain? Scans show liberals and conservatives have different brain structures". New York Daily News. Retrieved September 25, 2012.
- David M Amodio, John T Jost, Sarah L Master & Cindy M Yee, Neurocognitive correlates of liberalism and conservatism, Nature Neuroscience. Cited by 69 other studies
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- Jon Beckwith and Corey A. Morris. Twin Studies of Political Behavior: Untenable Assumptions? Perspectives on Politics (2008), 6 : pp 785-791
- Handbook of Social Psychology, Volume 1. Susan T. Fiske, Daniel T. Gilbert, Gardner Lindzey. p. 372.
- Carey, Benedict (June 21, 2005). "Some Politics May Be Etched in the Genes". The New York Times. Retrieved September 25, 2012.
- Alford, J. R.; Funk, C. L.; Hibbing, J. R. (2005). "Are Political Orientations Genetically Transmitted?". American Political Science Review 99 (2). doi:10.1017/S0003055405051579.
- Hatemi, P. K.; Gillespie, N. A.; Eaves, L. J.; Maher, B. S.; Webb, B. T.; Heath, A. C.; Medland, S. E.; Smyth, D. C.; Beeby, H. N.; Gordon, S. D.; Montgomery, G. W.; Zhu, G.; Byrne, E. M.; Martin, N. G. (2011). "A Genome-Wide Analysis of Liberal and Conservative Political Attitudes". The Journal of Politics 73: 271. doi:10.1017/S0022381610001015.
- Yoel Inbar, David A. Pizarro, Paul Bloom Conservatives are more easily disgusted than liberals Cognition & Emotion Vol. 23, Iss. 4, 2009
- Michael Bang Petersen. The evolutionary psychology of Mass Politics. In Roberts, S. C. (2011). Roberts, S. Craig, ed. Applied Evolutionary Psychology. Oxford University Press. doi:10.1093/acprof:oso/9780199586073.001.0001. ISBN 9780199586073.
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- "Is being liberal a choice?". Salon. March 5, 2013.
- Some Politics May Be Etched in the Genes - The New York Times,
- Political Views Reflected in Brain Structure - ABC
- Liberals and conservatives don’t just vote differently. They think differently. - The Washington Post
- Body politic. The genetics of politics. Slowly, and in some quarters grudgingly, the influence of genes in shaping political outlook and behaviour is being recognised - The Economist, Oct 6th 2012