According to a study appearing in the Journal of Politics, there is what the media have now dubbed a "liberal gene." If you carry a particular variant of the DRD4 gene affecting the neurotransmitter dopamine, you are more likely to turn out to be a liberal, say researchers from the University of California, San Diego, and Harvard University. If you have that strain, then you're more likely to seek out novel people and lifestyles different to the ones you're used to, leading you to have more liberal political opinions.
The researchers say it doesn't matter what your ethnicity, gender, age or culture to be a card-carrying liberal. You just can't fight genetics.
Fox News had a kind of field day with the study. Leading their story with: "Don't hold liberals responsible for their opinion--they can't help themselves."
Lead researcher James Fowler tells Fox News that it made more sense to be liberal in certain environments at specific points in human history, and in others a conservative ideology was merited. "And this is what made it possible for our species to survive," he explains. "If it made sense for us all to be liberal, natural selection would have made us all liberal."