We’re less than two years away from the 2016 presidential election, and politicians on both sides of the court are teasing constituents with their equivocal intentions of running. Republicans wait to see who among the contenders will officially throw their hat into the ring — Jeb Bush? Ted Cruz? Chris Christie? — while most Democrats are setting their sights on Hilary. Despite rallying cries for a more diverse and nonpartisan menu of candidates, the United States seems chronically mired in a two-party system for better or worse. In fact, there may be biological reasons for this reductionist dichotomy.

For starters, several studies have found brain structures that differ between conservatives and liberals. A larger anterior cingulate cortex was associated with leftist-leaning sympathies. This brain region is associated with, “Error detection, conflict monitoring, and evaluating or weighing different competing choices… [as well as] emotion regulation and cognitive control …” Furthermore, another study, “Found that greater liberalism was associated with stronger conflict-related anterior cingulate activity, suggesting greater neurocognitive sensitivity to cues for altering a habitual response pattern.”

On the other hand, brain scans of conservatives revealed a trend towards larger amygdalae, a part of the brain involved in “formation of emotional memories and learning, such as fear conditioning, as well as memory consolidation … Persons with a larger or more active amygdala tend to have stronger emotional reactions to objects and events, and process information initially through that pathway.” Additionally, research has demonstrated that right-leaning individuals experience more physiological responses and attentional focus to aversive stimuli. Put another way, “The aversive in life appears to be more physiologically and cognitively tangible to some people and they tend to gravitate to the political right.”

So, what exactly does this jargon mean for political orientation? Essentially, one could argue that a Republican finds the emotional aspects of a position more salient, while a Democrat relies more heavily on logical analysis. This follows soundly with the core value of each party: conservatives champion stability, while liberals are more comfortable with change. Predictably is less likely to stress an emotionally driven, aversive-conscious brain; adaptability is easier with a larger anterior cingulate cortex.

However, there are some documented similarities in those who identify with either of these political affiliations. The degree to which one zealously touts their beliefs — irrespective of whether they are conservative or liberal – seems to have a genetic component. Research conducted by Peter K. Hatemi and colleagues found that, “Genes exert little, if any, influence on party identification, directly or indirectly through covariates. However, we find that genes appear to play a pivotal role in shaping the strength of an individual’s party identification. With regard to political party affiliation, people appear to be influenced by a biological propensity to be intense or apathetic regardless of how they were raised or which party they were raised to support.”

Moreover, the most vehement among both parties exhibit similar brain activation when faced with evidence that reflected poorly on their chosen candidate. An Emory University study, led by Drew Westen, demonstrated that, “The part of the brain most associated with reasoning–the dorsolateral prefrontal cortex–was quiescent,” when one was confronted with information that undermined their beliefs. Notably, the most active parts of the brain were regions associated with emotion and conflict resolution. The “neural circuits engaged in rewarding selective behaviors,” were also triggered, after a fashion. Westen explains, “Essentially, it appears as if partisans twirl the cognitive kaleidoscope until they get the conclusions they want, and then they get massively reinforced for it, with the elimination of negative emotional states and activation of positive ones.”

One’s political beliefs are not exactly immutable, but this research helps us to better understand the biological underpinnings of an inclination that falls somewhere to the right or left of center. Of course, more research must be done to determine cause versus correlation.