why inequality is fatal

Nature | 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.

The Spirit Level: Why More Equal Societies Almost Always Do Better by Richard Wilkinson and Kate Pickett