The theory of everything

The opening sentence of their new book, The Spirit Level, cautions, "People usually exaggerate the importance of their own work and we worry about claiming too much" - yet by the time you reach the end you wonder how they could have claimed any more. After all, they argue that almost every social problem common in developed societies - reduced life expectancy, child mortality, drugs, crime, homicide rates, mental illness and obesity - has a single root cause: inequality.

And, they say, it's not just the deprived underclass that loses out in an unequal society: everyone does, even the better off. Because it's not absolute levels of poverty that create the social problems, but the differentials in income between rich and poor. Just as someone from the lowest-earning 20% of a more equal society is more likely to live longer than their counterpart from a less equal society, so too someone from the highest-earning 20% has a longer life expectancy than their alter ego in a less equal society.