Cory Clark, Brittany Liu, Bo Winegard, and Peter Ditto
Humans evolved in the context of intense intergroup competition, and groups comprised of loyal members more often succeeded than those that were not. Therefore, selective pressures have consistently sculpted human minds to be "tribal," and group loyalty and concomitant cognitive biases likely exist in all groups. Modern politics is one of the most salient forms of modern coalitional conflict and elicits substantial cognitive biases. Given the common evolutionary history of liberals and conservatives, there is little reason to expect pro-tribe biases to be higher on one side of the political spectrum than the other. We call this the evolutionarily plausible null hypothesis and recent research has supported it. In a recent meta-analysis, liberals and conservatives showed similar levels of partisan bias, and a number of pro-tribe cognitive tendencies often ascribed to conservatives (e.g., intolerance toward dissimilar others) have been found in similar degrees in liberals. We conclude that tribal bias is a natural and nearly ineradicable feature of human cognition, and that no group—not even one’s own—is immune.
Here is part of the Conclusion:
Humans are tribal creatures. They were not designed to reason dispassionately about the world; rather, they were designed to reason in ways that promote the interests of their coalition (and hence, themselves). It would therefore be surprising if a particular group of individuals did not display such tendencies, and recent work suggests, at least in the U.S. political sphere, that both liberals and conservatives are substantially biased—and to similar degrees. Historically, and perhaps even in modern society, these tribal biases are quite useful for group cohesion but perhaps also for other moral purposes (e.g., liberal bias in favor of disadvantaged groups might help increase equality). Also, it is worth noting that a bias toward viewing one’s own tribe in a favorable light is not necessarily irrational. If one’s goal is to be admired among one’s own tribe, fervidly supporting their agenda and promoting their goals, even if that means having or promoting erroneous beliefs, is often a reasonable strategy (Kahan et al., 2017). The incentives for holding an accurate opinion about global climate change, for example, may not be worth the social rejection and loss of status that could accompany challenging the views of one’s political ingroup. However, these biases decrease the likelihood of consensus across political divides. Thus, developing effective strategies for disincentivizing political tribalism and promoting the much less natural but more salutary tendencies toward civil political discourse and reasonable compromise are crucial priorities for future research. A useful theoretical starting point is that tribalism and concomitant biases are part of human nature, and that no group, not even one’s own, is immune.
A pre-print is here.