Diversity begets diversity in human cultures and mammal species

A key feature of the distribution of life on Earth is the positive correlation between environmental productivity and biodiversity. This correlation also characterizes the distribution of human cultural diversity, which is highest near the equator and decreases exponentially toward the poles. Moreover, it is now understood that the tropics house more biodiversity than would be expected from energy availability alone suggesting "diversity begets diversity". Here we show the same is also true for human cultural diversity. This convergence is particularly striking because while the dynamics of biological and cultural evolution may be similar in principle the mechanisms and time scales involved are very different. However, a common currency underlying all forms of diversity is ecological kinetics; the temperature-dependent fluxes of energy and biotic interactions that sustain life at all levels of biological and social organization. Using macroecological theory and the analysis of global databases we show both mammal diversity and cultural diversity scale superlinearly with environmental productivity at rates predicted by the ecological kinetics of environmental productivity. Diversity begets diversity in human cultures and mammal species because the kinetics of energy availability and biotic interactions result in superlinear scaling with environmental productivity.