The human body uses 30% to 50% less water per day than other primates:
The study compared the water turnover of 309 people with a range of lifestyles, from farmers and hunter-gatherers to office workers, with that of 72 apes living in zoos and sanctuaries.
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When they added up all the inputs and outputs, they found that the average person processes some three liters, or 12 cups, of water each day. A chimpanzee or gorilla living in a zoo goes through twice that much.
Pontzer says the researchers were surprised by the results because, among primates, humans have an amazing ability to sweat. Per square inch of skin, “humans have 10 times as many sweat glands as chimpanzees do,” Pontzer said.
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But the researchers controlled for differences in climate, body size, and factors like activity level and calories burned per day. So they concluded the water-savings for humans were real, and not just a function of where individuals lived or how physically active they were.
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One hypothesis, suggested by the data, is that our body’s thirst response was re-tuned so that, overall, we crave less water per calorie compared with our ape relatives. Even as babies, long before our first solid food, the water-to-calories ratio of human breast milk is 25% less than the milks of other great apes.
Another possibility lies in front of our face: Fossil evidence suggests that, about 1.6 million years ago, with the inception of Homo erectus, humans started developing a more prominent nose. Our cousins gorillas and chimpanzees have much flatter noses.
Our nasal passages help conserve water by cooling and condensing the water vapor from exhaled air, turning it back into liquid on the inside of our nose where it can be reabsorbed.
Having a nose that sticks out more may have helped early humans retain more moisture with each breath.
The other thing to consider is that humans mostly eat cooked food, which as I recall, requires a lot less water to process than the raw diet of apes.
There’s more than just a single adaptation that makes humans weird–Some of it is cultural, some of it is biological, and some is entirely indefinable.