Via The New York Times, an opinion piece by two major researchers: How Inequality Hollows Out the Soul. Excerpt (but read the whole article):
One of the well-known costs of inequality is that people withdraw from community life and are less likely to feel that they can trust others. This is partly a reflection of the way status anxiety makes us all more worried about how we are valued by others. Now that we can compare robust data for different countries, we can see not only what we knew intuitively — that inequality is divisive and socially corrosive — but that it also damages the individual psyche.
Our tendency to equate outward wealth with inner worth invokes deep psychological responses, feelings of dominance and subordination, superiority and inferiority. This affects the way we see and treat one another.
A few years ago, we published evidence that showed that in developed countries, major and minor mental illnesses were three times as common in societies where there were bigger income differences between rich and poor. In other words, an American is likely to know three times as many people with depression or anxiety problems as someone in Japan or Germany.
These differences are not a matter of awareness, definitions or access to treatment: To compare mental illness rates internationally, the World Health Organization asked people in each country about their mood, tiredness, agitation, concentration, sleeping patterns and self-confidence. These have been found to be good indicators of mental illness.
More recent studies have affirmed the pattern we found. One, looking at the 50 American states, discovered that after taking account of age, income and educational differences, depression was more common in states with greater income inequality. Another, which combined data from over 100 surveys in 26 countries, found that schizophrenia was about three times as common in more unequal societies as it was in more equal ones.
So what is happening?
In a study published in 2012, Sheri L. Johnson, a psychologist at the University of California, Berkeley, and colleagues reviewed a vast body of evidence from biological, behavioral and self-reported accounts, and concluded that a wide range of mental disorders might originate in a “dominance behavioral system.” This part of our evolved psychological makeup, almost universal in mammals, enables us to recognize and respond to social ranking systems based on hierarchy and power. One brain-imaging study discovered that there were particular areas of the brain and neural mechanisms dedicated to processing social rank.
Ms. Johnson concludes that psychiatric conditions like mania and narcissism are related to our striving for status and dominance, while disorders such as anxiety and depression may involve responses to the experience of subordination. Similarly, she suggests that the pressures of coping with social hierarchies may contribute to other conditions such as antisocial personality disorder and bipolarism.
If mental illness is related to dominance and subordination, you might assume that disorders like narcissism would be more common at the top of the social hierarchy while others, like depression, would occur more frequently at the bottom. The full picture, however, is more complicated.