Humans evolved in the context of intense intergroup competition, and groups comprised of loyal members more often succeeded than groups comprised of nonloyal members. Therefore, selective pressures have 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. The common evolutionary history of liberals and conservatives gives little reason to expect protribe biases to be higher on one side of the political spectrum than the other. This evolutionarily plausible null hypothesis has been supported by recent research. In a recent meta-analysis, liberals and conservatives showed similar levels of partisan bias, and several protribe cognitive tendencies often ascribed to conservatives (e.g., intolerance toward dissimilar other people) were 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.

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