Researchers in the US have found
a possible genetic cause for liberal political orientations. The DRD4 dopamine receptor gene has already found to be connected to neophilic tendencies (i.e., novelty seeking), and now it seems that those who have it are more likely to develop liberal political beliefs—though only if they have many friends during adolescence:
Lead researcher James H. Fowler of UC San Diego and his colleagues hypothesized that people with the novelty-seeking gene variant would be more interested in learning about their friends' points of view. As a consequence, people with this genetic predisposition who have a greater-than-average number of friends would be exposed to a wider variety of social norms and lifestyles, which might make them more liberal than average. They reported that "it is the crucial interaction of two factors – the genetic predisposition and the environmental condition of having many friends in adolescence – that is associated with being more liberal." The research team also showed that this held true independent of ethnicity, culture, sex or age.
Fowler concludes that the social and institutional environment cannot entirely explain a person's political attitudes and beliefs and that the role of genes must be taken into account. "These findings suggest that political affiliation is not based solely on the kind of social environment people experience," said Fowler, professor of political science and medical genetics at UC San Diego.
Of course, whether the gene would manifest in, say, social-democratic liberalism or guns'n'dope libertarianism would probably be influenced by cultural context. I recall reading about twin studies which showed pairs of twins raised apart holding similar political beliefs, though. (Or similarly structured; perhaps one could imagine, say, an authoritarian rightwinger growing up to be an authoritarian Stalinist, or a radical Marxist to be a radical Thatcherite neoliberal, in a different context.)