Humans are undoubtedly the most dominant species on Earth. But when did it begin? Understanding the origin of global human ecological dominance is central to discussions of the Anthropocene. We use macroecological rules, species distribution modeling, and bioenergetics to quantify how a world of just hunter-gatherers would compare to other populations of land mammals and to today’s human population of more than 7.8 billion.
Results/Conclusions
Species distribution models using environmental drivers of environmental productivity, biodiversity, and infectious disease burdens predicts a global carrying capacity of hunter-gatherers to be ~12 million people. Metabolic scaling suggests that hunter-gatherers, who were powered by biological metabolism of ~100 watts or ~2000 kcals/day/person, lived at densities below mammalian expectation (< 0.1 person/km2). In contrast to these estimates, modern humans now mostly residing in cities, occur at densities up to four orders of magnitude greater than hunter-gatherers and use up to ~10,000 watts per capita from calories and extra-metabolic energy mostly in the form of fossil fuels. Our preliminary analyses suggest that humans living as hunter-gatherers were appropriating energy similar to other land mammal species, per unit area, as well as globally. Total modern human metabolic (biological) energy use is still within the distribution of total energy use by other mammals. The combined effects of population and per capita energy use now exceeds global energy use by any other species and is approaching limits set forth by net global primary productivity.