Spring Books

Nature 458, 1109-1110 (30 April 2009) | doi:10.1038/4581109a; Published online 29 April 2009

Why inequality is fatal

Michael Sargent1

BOOK REVIEWEDThe Spirit Level: Why More Equal Societies Almost Always Do Better

by Richard Wilkinson & Kate Pickett

Allen Lane: 2009. 320 pp. £20

Why inequality is fatal

Why are our chances of reaching a great age so affected by wealth and status? The obvious answer is that more income buys better health. But it is a lot more subtle than that, as shown three decades ago by the Whitehall Study, in which epidemiologist Michael Marmot examined the death rates of British civil servants. To the surprise of many, he found that his subjects — all in continuous paid employment and with equal access to health care — were more likely to die in any given year if they were in a lower- grade job than a higher one. Marmot concluded that the employment hierarchy itself created status-dependent stress that affected the workers' health.

In their new book, epidemiologists Richard Wilkinson and Kate Pickett extend this idea with a far-reaching analysis of the social consequences of income inequality. Using statistics from reputable independent sources, they compare indices of health and social development in 23 of the world's richest nations and in the individual US states. Their striking conclusion is that the societies that do best for their citizens are those with the narrowest income differentials — such as Japan and the Nordic countries and the US state of New Hampshire. The most unequal — the United States as a whole, the United Kingdom and Portugal — do worst.

Many measures of the quality of life, including life expectancy, are correlated with the degree of economic equality in each country. A variety of problems such as mental illness, obesity, cardiovascular disease, unwillingness to engage with education, misuse of illegal and prescription drugs, teenage pregnancy, lack of social mobility and neglect of child welfare increase with greater inequality. Violence, from murder to the bullying of children at school, follows the same pattern. These trends are tied up with issues of trust: the authors chart a profound decline in trust in the United States from the 1960s to the present, which matches rising inequality during the long Republican ascendancy. The only statistic that defies the general trend is that for suicide, the incidence of which is higher in the most egalitarian countries, such as Sweden and Japan. Those who feel out of step with their country seem to blame themselves and not others.

The idea that income inequality within a society is more unsettling to health and welfare than income differences between societies has been hotly debated for more than two decades. In the past year alone, six academic analyses have been published in peer-reviewed journals, four of which contradict the hypothesis on statistical grounds. Yet Wilkinson and Pickett do not address these criticisms in their book. They might also have explained the occasional notable deviation from their theory, such as the unexpectedly high murder rates in egalitarian Finland and the unexpectedly low rates in very unequal Singapore.

How can inequality affect such a diverse set of social problems so profoundly? The authors make a compelling case that the key is neuroendocrinological stress, provoked by a perception that others enjoy a higher status than oneself, undermining self-esteem. This triggers the release of the hormone cortisol, which raises blood pressure and blood sugar levels, from which myriad health and social problems unfold. This seemingly hard-wired response has been well studied in social hierarchies of monkeys; low-status animals become predisposed to atherosclerosis and cardiovascular disease. Humans experiencing chronic stress exhibit similar symptoms, accumulating abdominal fat under the influence of a part of the brain associated with addiction.

Cortisol overrides 'feel-good hormones' such as oxytocin, involved in establishing trust, and dopamine, the reward signal that reinforces memory, attention and problem-solving ability. Cortisol-induced stress predisposes some individuals to mental illness or violent behaviour. It can hasten the arrival of puberty, which may prompt premature sexual adventures, providing a plausible explanation of the high prevalence of teenage pregnancies in the most unequal societies. Cortisol also transmits stress to a fetus, with lasting consequences for physical and emotional development.

The stress response could even exacerbate illiteracy and unwillingness to engage with education. Wilkinson and Pickett argue that these are more common in less equal societies, not because of poverty but because school-age students may lose self-esteem when they realize that some of their peers are better equipped than themselves for educational challenges. The stress response may also lead to illicit drug use. Monkey social hierarchies provide a clue: dominant animals secrete dopamine and feel good about their place in the world, whereas monkeys at the other end of the status scale are more inclined to self-medicate — with cocaine if given the opportunity.

The Spirit Level is a brave and imaginative effort to understand the intractable social problems that face rich democratic countries. For Wilkinson and Pickett, economic equality is the best way to improve the quality of life for all. Governments can get there by using redistributive taxation and an extensive welfare state, as in Sweden, or by restraining income disparities and minimizing public spending, as in Japan. The book ends optimistically: whatever route is chosen, the authors argue, the current economic slump may be a providential opportunity to start righting the balance.

  1. Michael Sargent is a developmental biologist at the National Institute for Medical Research in London and is author of Biomedicine and the Human Condition: Challenges, Risks and Rewards.
    Email: msargen@nimr.mrc.ac.uk


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