Salt, Sweat, and Survival The Strange Science of How Bodies Beat the Heat

On a hot afternoon on an open plain, almost every large mammal around you can outrun you. The antelope can, the horse can, and so can the lion, at least for a few hundred meters. But the sprint isn't what decides who survives an afternoon like that. What decides it is the number on an internal thermometer, and on that measure the human body is one of the most remarkable machines evolution has produced.

Most running animals overheat. A galloping antelope generates enormous quantities of metabolic heat, and its fur traps it. Its main escape valve is panting, which works, but with a catch. An animal can't pant efficiently while galloping, because its breathing is tied to the rhythm of its stride. So it has to stop, stand in the shade, and breathe heavily until its temperature falls. Humans have no such limit. We can run, walk, haul loads, and keep going while the air around us is hotter than our own skin, because we carry a cooling system across nearly our whole body surface.

This episode is about that system. We'll look at how sweat works, and why it is stranger and more costly than it seems. We'll examine the idea that our ancestors used it to wear down prey across the savanna. We'll ask how different human populations have tuned their bodies to different climates, and what is learned and what is inherited. And we'll finish at the frontier, where researchers are finding that the true limit of human heat tolerance sits lower than anyone assumed, in a world that is growing warmer.