Figure 2. Life history traits as functions of per capita energy use.

(a) Birthrate. The slopes linking birthrate to per capita energy use are similar for mammals and industrial populations and both are near the predicted value of −1/3¹². (b) Mortality under age five is a steeply negative function of per capita energy use (slope near −1) among industrial nations. (c) Lifespan. Curved solid line is an asymptotic fit to the industrial population data: log(lifespan) = 4.56+(4.84)*exp(−0.36*log(energy)). The dotted line is the linear fit to the nonhuman primate data. Note that the primate data are maximum lifespans whereas the industrial nations are life expectancy at birth. Exactly comparable data for primates would cause the primate data points to shift downward noticeably. (d) Age at first reproduction for industrial nations, nonhuman primates, and an average hunter-gatherer.