A lot has happened in the five years since we published our book, The Spirit Level.
In the UK, New Labour (the period in the history of the British Labour Party from the mid-1990s to the early 2000s, under former British prime ministers Tony Blair and Gordon Brown) were still perhaps too relaxed about people becoming “filthy rich.”
And there was an assumption that inequality mattered only if it increased poverty, and that for most people “real” poverty was a thing of the past.
How things change. In the aftermath of the financial crash and the emergence of Occupy, there has been a resurgence of public interest in inequality. About 80 percent of Britons now think the income gap is too large, and the message has been taken up by world leaders.
According to US President Barack Obama, income inequality is the “defining challenge of our times,” while Pope Francis argues that “inequality is the roots of social ills.”
The unexpected success of The Spirit Level owes more to luck than judgment.
We now feel a bit like the dog being wagged by its tail: In the past five years, we have given more than 700 seminars and lectures. We have talked to academics, religious groups, thinktanks, and to agencies such as the UN, the WHO, the Organisation for Economic Co-operation and Development (OECD), the EU and the International Labor Organisatio (ILO).
The truth is that we have deep-seated psychological responses to inequality and social hierarchy. Our tendency to equate outward wealth with inner worth means that inequality colors our social perceptions. It invokes feelings of superiority and inferiority, dominance and subordination — which affect the way we see, relate to and treat each other.
As we looked at the data, it became clear that, as well as health and violence, almost all the problems that are more common at the bottom of the social ladder are more common in more unequal societies — including mental illness, drug addiction, obesity, loss of community life, imprisonment, unequal opportunities and poorer well being for children.
The effects of inequality are not confined to the poor. A growing body of research shows that inequality damages the social fabric of the whole society.
When he found how far up the income scale the health effects of inequality went, Harvard professor Ichiro Kawachi, one of the foremost researchers in this field, described inequality as a social pollutant.
The health and social problems we looked at are between twice and 10 times as common in more unequal societies. The differences are so large because inequality affects such a large proportion of the population.
To the political defenders of inequality, the idea that too much inequality was an obstacle to a better society was a monstrous suggestion. They accused us of conjuring up the evidence with smoke and mirrors.
However, since our book, research confirming both the basic pattern and the social mechanisms has mushroomed. It is not just rich countries or US states where greater equality is beneficial, it is also important in poorer countries. Even the more equal provinces of China do better than the less equal ones.
Most important has been the rapid accumulation of evidence confirming the psychosocial processes through which inequality gets under the skin.
When we were writing, evidence of causality relied often on psychological experiments that showed how extraordinarily sensitive people are to being looked down on and regarded as inferior. They demonstrated that social relationships, insecurities about social status and how others see us have powerful effects on stress, cognitive performance and the emotions.