When you think about what separates humans from chimpanzees and other apes, you may think of our big brains or the fact that we move on two legs instead of four. But we have another distinguishing feature: water efficiency.
This is home to a new study that for the first time measures exactly how much water they lose and replace each day compared to our closest living relatives.
Our bodies constantly lose water: when we sweat, go to the toilet, even when we breathe. This water must be replenished to keep the volume of blood and other body fluids within normal limits.
Still, a study published March 5 in the journal Modern biology shows that the human body uses 30% to 50% less water per day than our closest animal cousins. In other words, among primates, humans have become a low-flow model.
An ancient change in our body̵
“Even just being able to stay a little longer without water would be a big advantage, as the early people began to make a living in dry savannah landscapes,” Ponzer said.
The study compared the water turnover of 309 people with different lifestyles, from farmers and hunter-gatherers to office workers, to that of 72 monkeys living in zoos and shrines.
To maintain fluid balance within a healthy range, the body of a person or other animal is a bit like a bathtub: “The water that enters must be equal to the water that comes out,” Ponzer said.
You lose water by sweating, for example, and the body’s thirst signals are activated by telling us to drink. Squeeze more water than your body needs, and the kidneys get rid of excess fluid.
For each individual in the study, the researchers calculated water intake through food and drink, on the one hand, and water lost through sweat, urine, and the gastrointestinal tract, on the other.
When they add up all the inputs and outputs, they find that the average person processes about three liters or 12 glasses of water each day. Chimpanzees or gorillas living in a zoo spend twice as much.
Ponzer says the researchers were surprised by the results because among primates, humans have an incredible ability to sweat. “People have 10 times more sweat glands per square centimeter of skin than chimpanzees,” Ponzer said. This allows a person to sweat more than half a gallon during a one-hour workout – the equivalent of two large sips of 7-Eleven.
Add to that the fact that great apes – chimpanzees, bonobos, gorillas and orangutans – live lazy lives. “Most monkeys spend 10 to 12 hours a day resting or eating and then sleep for 10 hours. They really only move a few hours a day,” Ponzer said.
But researchers are monitoring differences in climate, body size and factors such as activity levels and calories burned per day. Thus, they came to the conclusion that water savings for people are real, not just a function of where people live or how physically active they are.
Findings show that in the course of human evolution, something has changed that reduces the amount of water our body uses every day to stay healthy.
Then, as now, we could probably still survive only a few days without drinking, Ponzer said. “You’re probably not breaking the eco-leash, but at least you’re getting longer if you can stay without water longer.”
The next step, Ponzer says, is to point out exactly how this physiological change happened.
One hypothesis suggested by the data is that our body’s thirst response is readjusted, so we generally crave less water per calorie than our monkey relatives. Even as babies, long before our first solid food, the water / calorie ratio of human breast milk is 25% less than that of other great apes.
Another possibility lies ahead: Fossil data show that about 1.6 million years ago, with the advent of Homo erectus, humans began to develop a more noticeable nose. Our cousins gorillas and chimpanzees have much flatter noses.
Our nasal passages help retain water by cooling and condensing water vapor from exhaled air, turning it back into a liquid on the inside of our nose where it can be reabsorbed.
Having a nose that sticks out more may have helped early people retain more moisture with each breath.
“There is still a mystery to be solved, but apparently people are saving water,” Ponzer said. “Finding out exactly how we’re doing this is where we’re moving forward, and it’s going to be really fun.”
Elephants have been found to have the highest volume of daily water loss ever recorded in a terrestrial animal.
“Evolution of water saving in humans”, Herman Ponzer, Mary H. Brown, Brian M. Wood, David A. Reichlen, Audax. ZP Mabulla, Jacob A. Harris, Holly Dunsworth, Brian Hare, Kara Walker, Amy Luke, Lara R. Dugas, Dale Schoeller, Jacob Plange-Rhule, Pascal Bovet, Terrence E. Forrester, Melissa Emery Thompson, Robert W. Shumaker, Jessica M. Rothman, Erin Vogel, Francisco Sulistio, Shauhin Alavi, Didick Piglet, Samuel S. Urlacher and Stephen R. Ross. Modern biology, March 5, 2021. DOI: 10.1016 / j.cub.2021.02.045
Provided by Duke University School of Nursing
Quote: A new study suggests that humans have evolved to work with less water than our closest relatives (2021, March 5), obtained on March 5, 2021 from https://phys.org/news/2021-03 -humans-evolved-closest-primate-relatives .html
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