Hotter and sicker: External energy expenditure and the tangled evolutionary roots of anthropogenic climate change and chronic disease.

Journal Article (Journal Article)


The dual crises of climate change and chronic, or non-communicable, disease (NCD) have emerged worldwide as the global economy has industrialized over the past two centuries.


In this synthesis I examine humans' dependence on external (non-metabolic) energy expenditure (e.g., fire, fossil fuels) as a common, root cause in these modern crises.

Materials and methods

Using fossil, archeological, and historical evidence I show that the human lineage has been dependent on external energy sources since the control of fire in the Paleolithic. This reliance has grown with the development of agriculture, the use of wind- and water-power, and the most recently with industrialization and the transition to fossil fuels. To place industrialization in context I develop a Rule of 50, whereby individuals in industrialized economies consume roughly 50-times more external energy and manufacture roughly 50-times more material than do hunter-gatherers.


Industrialization and mechanization, powered by fossil fuels, have promoted centralization and processing in food production, reduced physical activity, and increased air pollution (including greenhouse gas emissions). These developments have led in turn to NCD and climate change.

Discussion and conclusion

Climate change and NCD are connected both to one another and to our species' deep evolutionary dependence on external energy. Transitioning to carbon-free energy is essential to reduce the existential risks of climate change, but will likely have only modest effects on NCD. With the impending exhaustion of oil, coal, and natural gas reserves, developing replacements for fossil fuels is also critical to maintaining our species' external energy portfolio.

Full Text

Duke Authors

Cited Authors

  • Pontzer, H

Published Date

  • July 2021

Published In

Volume / Issue

  • 33 / 4

Start / End Page

  • e23579 -

PubMed ID

  • 33629785

Electronic International Standard Serial Number (EISSN)

  • 1520-6300

International Standard Serial Number (ISSN)

  • 1042-0533

Digital Object Identifier (DOI)

  • 10.1002/ajhb.23579


  • eng