When you think about water efficiency, it might be difficult to fathom that humans have an advantage over their closest living animal relatives. However, a new study shows that people use as much as half the water that chimpanzees and other apes use daily.
This means that among primates, humans have evolved to be the “low-flow model,” which is good news.
Our bodies are constantly losing water through sweat, urination, and even when we breathe. That water needs to be replenished to keep blood volume and other body fluids within normal ranges. Being more water efficient offers the ability to better maintain fluid balances within a healthy range.
The study, published March 5 in the journal Current Biology, measured how much water humans lose and replace each day compared to those animals. It compared the water turnover of more than 300 people with a range of lifestyles to that of more than 70 apes living in zoos and sanctuaries. When all the numbers were added up, researchers found the average person processes about 12 cups of water daily while other primates were going through twice as much.
The findings suggest that something changed over the course of history to reduce the amount of water we need daily to stay healthy. A likely driving factor is an ancient shift in our body’s ability to conserve water that enabled our hunter-gatherer ancestors to venture farther from streams and watering holes in search of food, according to the study’s lead author.
One theory suggested by the data is that our body’s thirst response was re-tooled so that we crave less water per calorie compared to our ape relatives. Even as babies, long before our first solid food, the water-to-calories ratio of human breast milk is 25 percent less than the milks of other great apes. Another theory is that flatter noses helped us 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.
“There’s still a mystery to solve, but clearly humans are saving water,” said lead author Herman Pontzer, associate professor of evolutionary anthropology at Duke University. “Figuring out exactly how we do that is where we go next, and that’s going to be really fun.”