At the Washington Monthly there’s a book review by Chris Mooney of two recent works about the psychological and biological differences between liberals and conservatives.
The most rock-solid finding, simply because it has been shown so many times in so many different studies, is that liberals and conservatives have different personalities. Again and again, when they take the widely accepted Big Five personality traits test, liberals tend to score higher on one of the five major dimensions, [namely] “openness”: the desire to explore, to try new things, to meet new people…
Jonathan Haidt has covered this territory before. I often show this TED talk by Haidt to my ‘Introduction to Philosophy’ students.
Here’s the talk on YouTube.