Theory: Democrats may be biologically different from Republicans

[NoSheep]

I was in the thread that Skinner started where he asked what our ideas were on how we are all alike. What core values do we share as Democrats? And I thought about how the Democrats I know value critical thinking and logic. We seem to always be asking questions about right and wrong and I feel we all care about the world community of people enough that these things really matter to us. Our policy arises from that ability to look at the issues in a more or less unselfish way.
Republicans, on the other hand, seem to have an innate fear that prevents them from asking these important questions. They fear they will lose what they have. Or not come out on top.
I have observed that most behavior that I find objectionable, pathological, whatever, arises from a fear of something.
I wonder if it is possible, that those of us who are Democrats, are somehow biologically (as in brain chemistry) different from Republicans.
(This is not necessarily a nature/nurture question as I feel the slope between those is too slippery.)
I simply feel that there is a fundamental difference in the thought processes of the 2 parties and I think fear is what controls the right and their thinking, or lack thereof!
I'd appreciate thoughts on this. (Especially from folks more articulate than myself)