Energy and sociality in human populations.

In order to characterize and define human populations from a thermodynamic point of view, and considering that human societies are complex systems whose global description can be obtained by their energetic balance, the relationship was evaluated between individual energy consumption and the demographic and social-economic variables in all provinces of Spain. Pearson bivariate correlation, lineal regression analysis, and the coefficient of determination were applied. The results obtained show that individual energy consumption is associated with almost all the variables considered, in provinces with fewer than 400,000 inhabitants. However, in provinces having a population larger than 400,000, the association is reduced to about 50 percent. The positive or negative association between individual energy consumption and certain variables, especially those that determine reproductive success, suggests that the consumption of energy is explained both by the irreversible thermodynamics in relatively small populations and by the optimization principle in relatively large populations.