For the last decade, political science has been engaged in an effort to make all political behavior a function of biology, much the same way evolutionary psychologists make everything about sex. 

A new paper goes beyond suspect fMRI imaging interpretation and surveys of college students and makes the case that political leaning can be predicted by a preference for...body odor. 

Their basis is that mates appear to assort on religion and political attitudes more than any other social, behavioral, or physical trait. Most people do not overtly claim they have to marry a Democrat, even Psychology Today writers wouldn't claim something so speculative, but the authors read about attraction, ideology, and olfaction and decided that might subconsciously be a reason why.

They got 146 participants to rate the attractiveness of the body odor of unknown strong liberals and strong conservatives, without ever seeing the individuals whose smells they were evaluating. Based on that, they concluded that people find the smell of others with similar political opinions to be attractive, suggesting that one of the reasons why so many spouses share similar political views is because they were initially and subconsciously attracted to each other's body odor.

"People could not predict the political ideology of others by smell if you asked them, but they differentially found the smell of those who aligned with them more attractive. So I believe smell conveys important information about long-term affinity in political ideology that becomes incorporated into a key component of subconscious attraction," said Dr. Rose McDermott, lead author of the paper.

Citation: McDermott, R., Tingley, D. and Hatemi, P. K. (2014), 'Assortative Mating on Ideology Could Operate Through Olfactory Cues', American Journal of Political Science Sept 2 2014, DOI: 10.1111/ajps.12133. Source: Wiley