Economic activity is a strong predictor of environmental decline. Here we evaluate which aspects of the economy and of social institutions best predict biodiversity loss. In particular, we will examine how the distribution of wealth and income (economic inequality) affects biodiversity loss. Theory suggests that the relationship between inequality and environment should be U-shaped, with better conservation occurring at very high or very low levels of equality.  This has not yet been demonstrated empirically. In this analysis we examine how the size of the economy (GDP per capita) and the distribution of income in the country (Gini coefficient) can predict indices of environmental governance, and in turn how well environmental governance can predict the proportion of species in a country that are declining. Data was taken from 44 countries which together represent 53% of the Earth's inhabited landmass and 63% of its human population. Biodiversity decline was measured as the proportion of those species evaluated by the IUCN that were considered threatened in 2004. A model including population, GDP per capita, the number of native species, and the Gini coefficient was a strong predictor of threatened species (R squared = 0.85). In that model, the two most significant parameters were the number of species native to a country and the Gini coefficient. The proportion of species that are threatened increases by 1.5% for every 1% increase in the Gini coefficient. This indicates a potentially important role of economic distribution in determining the rate of species loss in a country.