Are liberals and conservatives fundamentally different types of people? The question fascinates sociologists and psychologists, but it's a very hard one to answer without sounding partisan. At Miller-McCune, Tom Jacobs notes this difficulty, reviewing various different theories about why liberals are liberals and why conservatives are conservative.

The general consensus appears to be that conservatives are less trusting than liberals: they are are "more easily threatened," for example, and more skeptical in areas where liberals might jump in head-first, "from immigration to foreign wars." But, asks Jacobs, "is there a way of explaining these differences that doesn't suggest one side or the other is wrong or aberrant?" He thinks evolutionary psychologist Jacob Vigil  comes pretty close.
His thesis, in a nutshell: Conservatives, being more oriented toward dominance, tend to acquire a larger group of friends and associates than liberals. They are more sensitive to potential threats because there are more people in their orbit, and thus the danger of their being hurt by a duplicitous person is greater. Liberals, being more inward-oriented, have smaller, tighter social groups and thus feel less threatened, which in turn allows them to be more open to unfamiliar experiences.
(Hat tip: Arts and Letters Daily)