Tom Stafford, a lecturer in neuroscience in Britain explains:
The idea that political views have a genetic component is now widely accepted – or at least widely accepted enough to become a field of study with its own name: genopolitics. This began with a pivotal study, which showed that identical twins shared more similar political opinions than fraternal twins. It suggested that political opinion isn’t just influenced by dinner table conversation (which both kinds of twins share), but through parents’ genes (which identical twins have more in common than fraternal twins). The strongest finding from this field is that the position people occupy on a scale from liberal to conservative is heritable. The finding is surprisingly strong, allowing us to use genetic information to predict variations in political opinion on this scale more reliably than we can use genetic information to predict, say, longevity, or alcoholism…
One candidate could be brain systems controlling our emotional responses. For instance, a study showed that American volunteers who started to sweat most when they heard a sudden noise were also more likely to support capital punishment and the Iraq War. This implies that people whose basic emotional responses to threats are more pronounced end up developing a constellation of more right-wing political opinions. Another study, this time in Britain, showed differences in brain structure between liberals and conservatives – with the amygdala, a part of the brain that learns emotional responses, being larger in conservatives. Again, this suggests that differences in political beliefs might arise from differences in emotional processes.
But notice that there isn’t any suggestion that the political opinions are directly controlled by biology. Rather, the political opinions are believed to develop differently in people with different basic biology. Something like the size of a particular brain area is influenced by our genes, but the pathway from our DNA to an apparently simple variation in a brain region is one with many twists, turns and opportunities for other genes and accidents of history to intervene on.