This story is part of Record High, a Grist series examining extreme heat and its impact on how — and where — we live.
Under the relentless sun in Africa, the birthplace of humanity, every living thing had to find a way to beat the heat. Lions rested in the shade, termites built giant ventilation mounds, and elephants evolved giant ears that could flap like fans. Around 2 million years ago, our ancestors perfected the weirdest technique of them all: pushing water from inside our bodies to outside, a gift for enduring sweltering temperatures.
Other animals can sweat a bit, but not like us. Running around in the heat, a person can shed more than two gallons of water each day, draining one of life’s precious resources at a speedy pace. As the body tries to cool down, blood vessels widen, redirecting hot blood from the core of your body toward…