Neural Basis of
Preference for Human Social Hierarchy versus Egalitarianism
By Joan Y. Chiao, Vani A. Mathur, Tokiko
Harada, and Trixie Lipkea, Department of Psychology, Northwestern University
and Northwestern University, Interdepartmental Neuroscience Program, Evanston,
Illinois
A
fundamental way that individuals differ is in the degree to which they prefer social dominance hierarchy over egalitarianism as a guiding principle
of societal structure, a phenomenon
known as social dominance orientation.
Here we
show that preference for hierarchical
rather than egalitarian social relations varies
as a function of neural responses within left anterior insula and anterior
cingulate cortices.
Our
findings provide novel evidence that
preference for social dominance
hierarchy is associated with neural
functioning within brain regions that are associated with the ability to share
and
feel concern for the pain of others; this suggests a neurobiological basis for social and political attitudes.
Implications
of these findings for research on the social
neuroscience of fairness, justice, and intergroup relations are discussed.
Key words: fMRI;
social dominance orientation; emotion;
anterior cingulate cortex; anterior insula; social hierarchy; egalitarianism;
empathy; political attitudes; justice
Introduction
One of the
oldest and most controversial dogmas
throughout human history is the notion
that some social groups are fundamentally superior to others. From Sir Francis Galton’s theory of eugenics
to the religious holy wars waged at
the turn of the first millennium AD, human history is rife with examples of intergroup conflict driven by an intrinsic belief in social dominance hierarchy
across groups and individuals.
Yet, recent
centuries have also seen the emergence of prominent
egalitarian philosophies, such as
Marxist socialism and Rawlsian liberalism, that challenge
the notion of human social dominance
hierarchy as a default mode by which groups and individuals should organize and function.
Such
heterogeneity of views reveals a spectrum
of ideals regarding fundamental questions about the extent to which social
dominance hierarchy or egalitarianism is preferable as a guiding principle in
our collective social life.
Social
dominance hierarchy is a core principle underlying social structure across the
animal
kingdom.
Across
species and human cultures, dominant social groups and individuals within the
hierarchy often have primary access to
precious resources (e.g., territory, food, mates) relative to those of lower rank.
Modern social
psychologists have discovered that people
vary in the degree to which they prefer
their own social group to dominate
others, a phenomenon
known as social dominance orientation (SDO).
Across
human cultures, SDO is a stable and unique personality trait that predicts a wide variety of social and
political attitudes.
For
instance, people who strongly prefer
social hierarchy (higher in SDO) have been shown to support political
ideologies that promote social hierarchy rather than egalitarianism (e.g., politico-economic
conservatism), oppose public policies intended to attenuate group-based social inequality
(e.g., civil rights, women’s rights, gay and lesbian rights), and seek societal
roles that reify dominance hierarchy within social institutions (e.g., law
enforcement rather than social work).
Notably, empathic concern is an important
attenuator of preference for social hierarchy. Individuals
who exhibit strong empathic concern, a capacity
to both share and feel concern for other people’s emotion, tend to prefer
egalitarian rather than hierarchical social relations between groups.
Despite a
solid understanding of how SDO affects a wide range of social cognition and behavior,
little is known about the neurobiological
mechanisms underlying an individual’s preference for social dominance
hierarchy versus egalitarianism.
Because of
the near ubiquitous presence of social hierarchy across species and cultures,
it is
plausible
that the human ability to successfully navigate
hierarchical social interaction arises
from adaptive mechanisms in the mind and brain that support the emergence and maintenance
of social hierarchies within and across social groups.
Given the
prior social psychological evidence that empathic concern is inversely related
to preference for social hierarchy, we examined the possibility that neural regions
associated with empathy underlie the preference for human social hierarchy.
Empathya is supported by a distinct neural matrix of limbic and
paralimbic brain regions,
including anterior insula (AI), anterior cingulate
cortex (ACC), lateral cerebellum, and
brainstem.
AI and ACC
are two major regions of the pain matrix thought to code the autonomic and affective
dimension of pain and, in particular, the subjective experience of empathy when
perceiving pain or distress in others. AI is thought to support experience of
social emotions while ACC is thought to code the affective components of pain.
Prior
evidence suggests that empathic neural responses within AI and ACC can vary as
a function of several modulatory factors of the empathizer, such Empathy is a
term that can refer to a number of distinct affective and cognitive processes.
Here we
use the termempathy to refer to individuals’ ability to both share and feel
concern for other people’s emotional welfare. as their gender, age, and
dispositional empathy. Although the
relationship between activity in AI and ACC and the affective components of
empathic concern are well established,
the neural
basis of preference for social dominance hierarchy or egalitarianism remains unknown.
Here we
used functional magnetic resonance imaging (fMRI) to examine the association
between SDO and empathic neural responses during perception of pain in others.
We
hypothesized that the degree of preference for social dominance hierarchy would
significantly vary as a function of neural responses associated with empathy
when controlling for other known modulatory factors, such as gender, age, and
dispositional empathy.
Correlation between SDO and Empathic Neural
Response
Consistent
with our neural predictions, the degree of SDO correlated significantly and negatively
with response to perceived pain in others within left AI and ACCs.
Additional
regions that showed significant correlation with SDO and neural response to
painful relative to neutral scenarios include regions previously associated
with the mirror neuron system, including right inferior parietal lobe and left
inferior frontal gyrus .
There were
no additional significant correlations between left AI and ACC activation and age
and dispositional empathy. Multiple regression analysis indicated that SDO was
the only significant negative predictor of left insula and ACC activity
controlling for age and dispositional empathy (e.g., all IRI subscale scores
separately).
Discussion
Our
findings show for the first time that individual differences in the preference
for social dominance hierarchy predict neural response within left AI and ACCs.
Individuals
who indicated a greater desire for social dominance hierarchy showed less
response when perceiving pain in others within fronto-insular regions critical
to the ability to share and feel concern for the emotional salience of another
person’s misfortune. This modulation of fronto-insular neural responses by preference
for social hierarchy and egalitarianism is not explainable by other characteristics
of the empathizer, such as gender, age, or dispositional empathy.
Activation
of ACC in response to other people’s pain observed in the current study is
consistent
with a number
of prior studies showing that ACC responds to one’s own experience of pain as
well as knowledge that another person is in pain, a process that is thought to
reflect neural simulation of their pain.
In
addition to coding the affective attributes of pain, ACC has also been
previously associated with self-regulation and conflict-monitoring, a process by
which individuals detect when their habitual
response
is incongruent with the appropriate response given the current situation.
A recent study
showed that stronger conservatism is
associated with less neurocognitive
sensitivity
to response conflicts and greater
persistence in habitual response patterns.
By
extension to the current study, we show that individuals who prefer social hierarchy across social groups and
individuals (e.g., politico-economic conservatism) show less neuroaffective sensitivity to other
people’s pain.
Hence,
activity within the ACC reflects both affective and cognitive processes that
contribute to the neurobiological basis of political attitudes.
These
findings compliment growing evidence of a pivotal role for insular cortex and social emotions
in judgments of fairness and justice.
Anthropologists,
sociologists, and economists have documented a number of instances in economic
games whereby humans will reject a monetary reward if they perceive it as
unfair relative to the rewards that others are receiving, a phenomenon known as
“inequity aversion.”
Recent
neuroeconomic studies have associated insular
cortex activity with inequity
aversion during economic exchanges. In one prior neuroimaging study, greater
insula activity predicted the likelihood
of
rejecting an unfair offer of monetary reward for one’s self during the ultimatum game.
A more
recent neuroimaging study showed that activity within insular cortex similarly
predicted
the
likelihood that a person would reject an unfair allocation of monetary
resources for other
people
during a charitable donation task.
The recruitment
of insular cortex in the experience of physical and moral disgust indicates
that social emotions underlie one’s aversion for inequitable monetary offers
both for one’s self and others.
Importantly,
our results broaden this notion by showing that insula activity is associated not only with aversion to inequity during economic exchanges (e.g., whether one
accepts a fair or unfair monetary allocation for oneself or another person) but
more generally with an aversion for any
kind of group-level social inequality (e.g., whether different social
groups should have equal right to vote or equal access to educational
opportunities).
Because social dominance orientation has been
shown to be reliably associated with preference for
social
hierarchy across many different kinds of social systems (e.g., economic,
political, religious,
educational),
the inverse relationship between empathic neural response and SDO observed in
the current study suggests that insular cortex
codes aversion to inequality across a broad range of social situations,
from decisions made during small-scale economic interactions to those involving
support for social and political attitudes that shape large-scale social and political
systems.
The extent
to which a person is able to share the emotional
salience of another person’s pain or misfortune may subsequently guide their preference for political
ideologies, public policies, and societal roles that either promote or attenuate group-based social hierarchy and intergroup
conflict.
Future
research is needed to determine the precise
causal relationship between preference for social hierarchy or
egalitarianism and empathic neural response.
Nevertheless,
the current evidence reveals SDO as a
unique modulator of fronto-insular regions and suggests that these regions may serve as a neural foundation for
social and political attitudes underlying prosocial behavior.
Address for correspondence: Joan
Y. Chiao, Department of Psychology, Northwestern University, 2029 Sheridan
Road., Evanston, IL 60208. Voice:+1 847 467 0481; jchiao@northwestern.edu
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