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
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
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
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).
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; email@example.com