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 the surface. In tandem, sweat glands pump water, drawn from that blood, onto your skin. When those tiny beads evaporate, they carry heat off the body and into the air.
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