Predisposed: Liberals, Conservatives, and the Biology of Political Differences, by John Hibbing, Kevin Smith & John Alford (2014). The Political Science Department at the University of Nebraska has a research lab attempting to explain the differences between liberals and conservatives, based on surveys and biological experiments (e.g., eye tracking, gaze cuing, brain imaging, genetics, EEG). To begin with, the Wilson-Patterson Index of Conservatism is a set of questions that captures left/right differences. The Appendix to the book has 20 questions, such as: "Which lesson is more important to teach to children? a) kindness or b) respect." This was a tough one for me; eventually I answered respect. I scored 10 out of 20, right in the middle (note that if you divide the results exactly in half, I'm a conservative (as is anyone scoring 1-10). Other questions give clear differences: Are you: eccentric or conventional, decisive or flexible, open-minded or moralistic, imaginative or practical, and simple or complex.
Conservatives seem to be more conscientious, believe in self-reliance, authority, hierarchy and order, and favor traditional values. Conservatives favor black vs. white categories and avoid ambiguity. The left focuses on equality, tolerance, departure from tradition, sees levels of gray and tolerates ambiguity. Big differences occur in traditional values and moral codes (both favored by conservatives), treatment of out-groups and rule-breakers (with liberals more sympathetic), roles of groups and individuals (conservatives favoring merit and personal liberty, liberals favoring needs, community actions and responsibilities), plus experiences (traditional for conservatives, new for liberals). Liberals see the "undeserving rich," while conservatives see the "undeserving poor." Conservatives focus more on the negative and public policy focuses more on security and authority to mitigate the bad stuff.
Hibbing et al. reviewed various psychology research and reinterpreted the findings. Milgram for example ran his famous electric shock experiments in the 1950s. Subjects were willing to shock "students" who failed to answer questions under authority figure up to 450 volts. However, not all did. Milgram viewed this as the importance of authority for promoting bad behavior. Hibbing and gang noted a large percent did not comply, suggesting these were non-conservatives. The infamous Stanford prison experiment found subjects randomly assigned as guards and prisoners quickly assumed these roles and guards soon acted brutally. Again, not all acted this way. The dictator game and ultimatum game showed how people could act selfishly, but most did not. Behaviorist BF Skinner's experiments with animals led to the conclusion that external rewards and punishments dominate (ignoring individual behavior, which Hibbing did not), assuming that humans act the same (an approach seemingly adopted by economists, like for executive compensation).
Much of the rest of the book considers biological (including genetics) measures that support the conservative/liberal split, yielding the same general results and concluding its not just culture but biology. The disappointing part for me was the lack of focus on the middle. Some number of us (say one third) are moderates. I would have liked them to look at various distribution categories, say graphs by Wilson-Patterson scores, analysis by quartiles, whether the distribution is roughly normal or peak at the extremes, etc. I don't view this as a fatal flaw and think this is an excellent book. Looking specifically at moderates seems to be another set of academic articles and book.