Tribalism is Human Nature
**In press; Current Directions in Psychological Science; as of June 10, 2019**
Cory J. Clark
Brittany S. Liu
Bo M. Winegard
Peter H. Ditto
University of California, Irvine
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.
Keywords: politics, bias, symmetry, tribal loyalty, intergroup conflict
Tribalism is Human Nature
The human mind was forged by the crucible of coalitional conflict (Geary, 2005). For
many thousands of years, human tribes have competed against each other. Coalitions that were
more cooperative and cohesive not only survived but also appropriated land and resources from
other coalitions and therefore reproduced more prolifically, thus passing their genes (and their
loyalty traits) to later generations (Tooby & Cosmides, 2010). Because coalitional coordination
and commitment were crucial to group success, tribes punished and ostracized defectors and
rewarded loyal members with status and resources (as they continue to do today). Thus, displays
of loyalty and commitment to other members of the tribe also enhanced individual-level fitness
(by increasing status and resources and minimizing risks of ostracization). Over time, this would
select for traits that signal and enhance coalitional commitment (Berreby, 2005) such as ingroup
favoritism (Tajfel & Turner, 1979). Tribalism, therefore, is natural.
Although tribal loyalties inspire many noble behaviors, they can impel humans to
sacrifice sound reasoning and judgmental accuracy for group belonging and commitment
(Kahan, Peters, Dawson, & Slavic, 2017). In other words, tribal loyalties can lead to tribal
biases. For example, people selectively approach information that supports their tribe’s interests
and avoid information that has potential to harm their tribe (by watching particular news
networks, or by forming “echo chambers” in their social environments; Stroud, 2010). And
people evaluate information they are exposed to in a biased manner by being uncritically
By tribe, we simply mean a human social group sharing a common interest, and by tribalism,
we mean tendencies to be loyal to and favorable toward one’s own tribe (and less favorable
toward other tribes). By human nature or natural, we mean evolved human propensities that
develop in most humans.
accepting of information that supports their tribe’s agenda and more skeptical of information that
opposes it (Ditto et al., 2018). These kinds of cognitive biases are problematic because (1)
post-enlightenment societies prize reason and rationality and no longer explicitly tolerate
obvious displays of ingroup favoritism, and (2) modern governments require the coordination of
multiple groups (e.g., political groups) to function. Biases decrease the likelihood of consensus
as groups fail to agree even on the facts in a particular debate.
There are at least two reasons tribalism distorts beliefs. First, beliefs display and signal
loyalty to group goals. Asserted opinions at least partially function as behavioral intention
indicators and therefore as coalitional membership indicators (Pietraszewski, Curry, Petersen,
Cosmides, Tooby, 2015). When one asserts “Abortion is immoral,” one indicates willingness to
coordinate with others to regulate abortion. Coalitions that generally oppose abortion (e.g., the
modern GOP) react negatively toward putative members who assert skepticism about pro-life
principles (Ditto & Mastronarde, 2009) because this indicates an unwillingness to cooperate on
that goal. If beliefs are held fervently, compel strong emotional displays, or are costly to hold,
they might function as honest (and thus trustworthy) loyalty signals (Kurzban & Christner,
2011). Perhaps perversely, dogmatism and resilience to contrary evidence likely enhance the
persuasiveness of the signal, because they show that one is strongly dedicated to the group’s
ideology in spite of potential consequences (e.g., being wrong about a difficult to answer
Second, beliefs are precursors to potential arguments that support the interests of the
group, which coalitions are often formed to pursue and protect (e.g. wealthy people who want
low tax rates). In modern societies, violence is verboten, so tribes prevail not by conquering
other tribes, but by persuading other people—often, by making arguments. Sincere beliefs
generally lead to better and more zealous arguments than cynical hypocrisy (von Hippel &
Trivers, 2011). Therefore, people are motivated to favor and believe information that promotes
their group’s interests and to resist information that opposes their group’s interests because it
makes them more persuasive proponents of their group’s cause (Kahan, Jenkins-Smith, &
These two reasons also likely explain why politics appears to be one of the most fertile
grounds for bias (Van Bavel & Pereira, 2018). Political contests are highly consequential
because they determine how society will allocate coveted resources such as wealth, power, and
prestige. Winners gain control of cultural narratives and the mechanisms of government and can
use them to benefit their coalition, often at the expense of losers. Given these high stakes,
motivations to signal group loyalty and to defend the positions of the group are likely
particularly powerful in politics.
Within the political domain, individuals appear most biased about those issues most
important to the group, which often include moral commitments (Ditto, Pizarro, & Tannenbaum,
2009). As noted above, moral commitments signal that one is willing to conform to the rules of
the coalition. Therefore, groups are particularly prone to giving status to those who conform to
and vocalize support for moral norms and to deducting status from those who rebel and vocalize
dissent against those norms (Descioli & Kurzban, 2013). Thus, we can expect tribal biases to be
especially large for important moral commitments (Tetlock, 2002). For example, if opposing
abortion is a central goal for the political right, conservatives will be particularly biased about
facts surrounding abortion. If enhancing the status of women in society is a central moral goal of
the political left, liberals might be particularly biased about facts surrounding the gender wage
However, humans also care about truth and accuracy (for obvious evolutionary reasons),
and so biases are most likely to emerge for issues where the truth is ambiguous (Munro, Weih, &
Tsai, 2010). Many if not most political (and moral) disagreements are about ambiguous issues.
Experts disagree about when a fetus or child can experience conscious pain and about the many
contributors to the gender wage gap (and even the size of it). Even if experts could agree on the
facts, political positions often reflect opinions about what ought to be the case (often subjective
beliefs) based on beliefs about what is the case (ideally objective facts). For example, if the
within-profession wage gap is largely due to women’s choices to work fewer hours, should they
be paid the same as men? Policy choices often involve painful and complicated tradeoffs (e.g.,
interfering with free market autonomy to reduce income inequality, investing in new and more
costly energy technology to minimize climate change).
When the truth is ambiguous, tribal biases are more powerful because argument is more
important than when the truth is clear. Groups do not debate whether trees exist because the
answer is virtually undeniable. They do, however, debate whether fetuses deserve various legal
protections or whether women are paid less than men for equal work, because there are
intelligent arguments on both sides of these issues and there is no one obvious correct answer.
There is an unfortunate tribal logic here. One might imagine that ambiguity would compel
humility and confessions of uncertainty, but when ambiguity occurs in the context of coalitional
conflict, it may actually increase epistemic arrogance and bias. This is perfectly sensible,
however, if we remember that humans are coalitional animals, not dispassionate reasoners. They
were not “designed” to be humble; rather, they were “designed” to conform and to protect the
status of their tribe (Kahan et al., 2017).
Our guiding assumption, then, is that tribal bias is a nearly ineradicable element of human
nature and that it causes predictable cognitive biases (those that benefit the self and the group).
Specifically, people will be biased in favor of their tribe, particularly for issues important to the
tribe (often moral issues) and particularly when ambiguity is high and therefore the importance
of argument and persuasion is high. Given that modern liberals and conservatives share
evolutionary histories that favor loyalty signals and tribal biases, it is a priori likely that the
psychological propensities for bias would be similar on the political left and right. We call this
the evolutionarily plausible null hypothesis and recent research has supported it.
Everyone’s a Little Bit Biased…
Social sciences for a long time focused especially on the biases of conservatives, with
some scholars arguing that conservatives are more biased than liberals (e.g., Jost, Glaser,
Kruglanski, & Sulloway, 2003).
But in recent years, researchers have pushed back against this
narrative, contending that the overwhelming preponderance of liberals in the social sciences may
have skewed research about political ideologies and the people who hold them. Liberals likely
see their own biases as truths (Pronin, Lin, & Ross, 2002) and see conservative beliefs as
peculiar and wrong; therefore, they seek to explain the “conservative mind” and its perplexing
biases (Duarte et al., 2015; Eitan et al., 2019).
This insight inspired Ditto and colleagues (2018) to conduct a meta-analysis to test these
competing hypotheses. Across 51 experiments that tested the tendency for liberals and
Likely all political tribes display group loyalty biases, but the majority of this work has been
conducted in the U.S., so we focus on U.S. politics here. Future work should examine these
patterns in other political systems.
conservatives to evaluate identical information more favorably when it supports their own
political commitments than when it opposes them (for example, a death penalty supporter
evaluating scientific methods as more valid when the results of those methods support rather than
oppose the deterrent efficacy of the death penalty), there was strong support for the symmetry
hypothesis: liberals and conservatives were both biased, and to virtually equal degrees. Because
the included studies were performed under tightly controlled laboratory conditions, these results
cannot tell us how liberal and conservative biases might vary over time and context, but they do
suggest that liberals and conservatives share the same basic psychology that leads to bias—and
to similar degrees. This finding is consistent with the evolutionarily plausible null hypothesis:
tribal bias is natural, and thus all political tribes should be similarly susceptible to it.
Whereas earlier scholars often emphasized that conservatives were higher in proclivities
that ought to predict stronger biases (than liberals) such as authoritarianism and dissonance
avoidance, a new wave of research in social psychology suggests that many of these proclivities
exist in equal levels in conservatives and liberals. As can be seen in Table 1, these include
authoritarianism, discrimination, dissonance avoidance, prejudice, selective exposure, and
resistance to science. For example, although researchers previously thought conservatives were
more intolerant of dissimilar others, such results may have been due to confounds between the
target groups investigated by liberal researchers (e.g., African Americans) and the political
ideology of the target groups (e.g., African Americans tend to be politically liberal). More recent
work suggests that people exhibit higher intolerance toward groups perceived as more dissimilar
to their own group, and to similar degrees for liberals and conservatives (Brandt, Reyna,
Chambers, Crawford, & Wetherell, 2014).
Table 1. Recent work demonstrating more symmetry between liberals and conservatives than
Left-wing authoritarianism exists, and
predicts similar outcomes as right-wing
Conway, Houck, Gornick, &
Liberals and conservatives similarly
endorse more discrimination against
groups that violate their values than
groups that do not
Wetherell, Brandt, & Reyna,
Liberals and conservatives similarly
avoid writing counter-attitudinal essays
Collins, Crawford, & Brandt,
Liberals and conservatives are similarly
intolerant toward ideologically
dissimilar and threatening groups
Brandt et al., 2014
Liberals and conservatives have similar
negative reactions to dissonant science
Liberals and conservatives similarly
deny scientific interpretations of results
that conflict with their attitudes
Nisbett, Cooper, & Garrett,
Washburn & Skitka, 2018
Liberals and conservatives are similarly
averse to learning the views of
Extreme conservatives demonstrate the
most selective exposure, but moderate
conservatives demonstrate the least
Frimer, Skitka, & Motyl,
Salem, & Ditto, 2017
This does not mean that conservatives and liberals are similar in all ways or that one
group will never be vastly more biased or incorrect than the other—they will (Federico & Malka,
2018; Ditto et al., 2019). Groups, as we have argued, are most biased about issues that are
morally important and ambiguous. The general psychological propensities for bias appear similar
on the political left and right, but there are predictable domain-specific asymmetries in bias.
To consider a few examples, conservatives appear more motivated to reject
anthropogenic climate change than liberals, likely because it seems to support government
regulation and more centralization and hurts the fossil fuel industry, an important part of the
Republican base in the United States (Lewandowsky & Oberauer, 2016). Conservatives may also
exaggerate the amount of choice people exercise over their sexuality because homosexuality is
considered immoral by a substantial proportion of the religious believers in the Republican
coalition (Haider-Markel & Joslyn, 2008), and contending that it is a free decision rather than an
innate inclination is more compelling for moral condemnation (Clark, Baumeister, & Ditto,
2017). On the other hand, a growing body of work suggests that liberals in general are more
biased than conservatives about traditionally conceived disadvantaged groups (e.g. women,
Blacks; see Table 2), likely because an important moral value of the political left is opposition to
inequality (Jost, Nosek, & Gosling, 2008).
Table 2. Recent work documenting a domain-specific bias asymmetry about disadvantaged
groups such that liberals are more biased than conservatives
All political orientations demonstrate a pro-black bias, but higher
liberalism was associated with a larger pro-black bias
Axt, Ebersole, &
Liberals were more willing to make a utilitarian sacrifice of a White
man’s life than of a Black man’s life, whereas race had no influence on
Whereas liberals are more inclined to amplify the successes of
disadvantaged groups (i.e., Blacks, women) than advantaged groups
(i.e., Whites, men), conservatives treat the successes of both groups
White liberals present less self-competence to Black than White
interaction partners, whereas White conservatives treat the groups more
Dupree & Fiske,
Liberals are biased against the notion that there could be biological
differences between demographic groups when those differences appear
to favor advantaged groups, whereas conservatives display less of a bias
A study from a political bias meta-analysis with the closest relevance to
disadvantaged groups (affirmative action and same-sex marriage) found
one of the largest effect sizes for liberal bias (Crawford, Jussim, Cain, &
Ditto et al. (2018)
Note that if one group currently has more or stronger concerns (because of historical and
time variant factors such as rapidly changing demographics or having recently lost a presidential
election), or if one group has more moral convictions in general, one might predict more bias in
that group (during that time period, or in general). However, our best current estimate is that
domain-specific asymmetries between liberals and conservatives appear to produce general
symmetries in pro-tribe biases among liberals and conservatives when averaged across multiple
domains (and over at least a brief period of time). Until newer or better information contradicts
these recent findings, it seems reasonable to posit that liberals and conservatives are roughly
symmetrical in their pro-tribe cognitive tendencies.
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
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.
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1. Ditto et al., 2018 (see References): A meta-analysis of partisan bias studies (which found
liberals and conservatives showed an equivalent tendency to evaluate politically congenial
information more favorably than politically uncongenial information), including a discussion
of how to reconcile conflicting literature on the question of symmetry in partisan bias.
2. Eitan et al., 2019 (see References): An article demonstrating the extent to which political
social psychology research can be affected by liberal viewpoints and values.
3. Van Bavel and Pereira, 2018 (see References): A comprehensive and topical overview on
ways in which partisan identity can affect individuals’ cognition, judgments, and decision-
4. Kahan, Peters, Dawson, and Slavic, 2017 (see References): An article for understanding how
motivated reasoning in politics serves to maintain individuals’ standing in important ingroups
(e.g., based on political identity).
5. Federico and Malka, 2018 (see References): Example of a review article that challenges the
notion that conservative ideology is invariably linked with certain psychological dispositions
and argues instead that the association is often dependent on various factors, such as issue,
context, and group loyalty.