It is a modern curiosity that there is an ideological belief that holds there are no differences between men and women or between people of different ethnic heritages, that all apparent differences are a result of social construction. It is a magical belief that flies in the face of all accepted evidence. The differences are real, replicable and consequential. The fact that there are real and replicated measures of difference does not in any fashion challenge the core and critical belief that "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness."
Equal rights has nothing to do with the unique physical and cultural endowments of each person.
But those who are ideologically happy to ignore attribute variance among individuals hold out for one critical exception. They wish to believe that there are mental, physical and psychological differences between "conservatives" and "liberals." Given the epistemological slipperiness of both terms and their constant evolution over time, it would seem nonsensical on its face to hold that there are fundamental and permanent differences. But the belief is deep rooted and over the years there has been a steady flow of research papers of varying (but usually low) quality purporting to show that conservatives have lower IQs, are more inclined to magical thinking, have more limited domains of knowledge, or have a different neurological and psychological make-up than liberals. Or vice-versa.
I usually ignore these findings after confirming what is almost always the case: poor study protocols, small sample sizes, non-randomization of subject population, low effect sizes, etc. Each study makes a splash, excites the bigots and then disappears owing to non-replication.
Wendell looks at three claims and finds that there are no material objective differences between humans regardless of their belief systems. From the abstract:
Do conservatives and liberals have differing sensitivities to avoidance, inhibition, and negative emotion? Do psychological factors beneath our conscious awareness underlie the political ideologies we embrace? Political science researchers have broken new ground over the past ten years in our understanding of the psychology and physiology of political ideology. However, large questions remain about how political ideology may be related to avoidance motivations and negative emotion. This work expands our current knowledge in this area by presenting three studies with multiple methodologies: original survey data, electroencephalographic measurements, and behavioral experiments in a lab setting. Working in the tradition of J.A. Gray’s dual systems of behavioral motivation, I explore how political ideology is related to several related dispositional measures of behavioral avoidance, behavioral inhibition, and negative affectivity. Overall, and in contrast to literature expectations, my evidence suggests that liberals and conservatives do not have persistent differences in avoidance sensitivity or negativity bias. While strong evidence remains demonstrating important dispositional differences between liberals and conservatives, additional research will be required before researchers can conclude that conservatives are uniquely motivated by psychological avoidance or negative affect.UPDATE: I corrected my final sentence to include the typographically omitted, but strategic, "no"