Where does political orientation come from?

Twin studies within political science consistently indicate that 40–60% of the variation in adult political orientations is heritable. The notion that this variance being attributed to genes is in reality entirely due to a combination of nonpolitical early childhood environmental similarity (i.e., being dressed alike or sharing a bedroom), the mutual influence of a sibling, prepartum in utero environment, physical appearance, and the seemingly inherent tendency to treat others differently based on these (biologically based) appearances strikes us as extremely unlikely. But even if it is, key elements of this argument—in utero environment, the genetics of physical appearance—automatically bring its adherents into agreement with our central point: that political science must increase the absorption of biological variation into its epistemology. Critics and proponents of twin studies are in general agreement that a wholly nonbiological paradigm for the acquisition of political attitudes will unnecessarily limit progress. Our analysis here certainly reinforces that conclusion while also advancing empirical support for a model of gene-environment interaction that gives both nature and nurture their due.

That is from the article "Biology, Ideology, and Epistemology: How Do We Know Political Attitudes Are Inherited and Why Should We Care?" by Smith et al. (American Journal of Poltical Science, January 2012).
More on the topic is here.