Why is the mutual trust of British lower than Japanese? Why is teen pregnancy rate in the United States higher than France? Why are Swedes thinner than Australians? All social problems point to the same answer. The effect of social justice and income distribution on human society is surprising. With a large number of accurate statistics, The Spirit Level: Why Equality is Better for Everyone reveals the non-negligible influence of inequality on the mutual trust, life span, teen pregnancy, obesity, mental illness, crime rate, social mobility, education and other aspects of every member in the society.