- Researchers are discovering a new feature of human evolution.
- Humans have evolved to use less water per day than other primates.
- The nose is one of the factors that can make people water efficient.
Scientists have discovered a new feature that distinguishes humans from other primates such as chimpanzees. The research shows that the human body uses 30% to 50% less water per day than our closest animal relatives.
Sure, our brain power and the ability to walk upright are critical to making us special, but the efficiency with which the human body uses water is another big difference. This trait likely originated as an evolutionary adaptation in ancient hunter-gatherers, who had to search farther from water sources in search of food, thinks lead author of the study Herman Pontzer, associate professor of evolutionary anthropology at Duke University.
“Even if we could go without water just a little bit longer, that would have been a big advantage, as the early humans began to live in arid savannah landscapes,” Pontzer said.
Since our body is constantly losing water through processes such as urination or sweating, it is imperative that the water level be restored. “To sustain life, humans and other land animals must maintain a tight balance between water increase and water loss every day,” write the paper’s authors.
For the study, the researchers looked at this cycle of water use and loss in 309 people from different backgrounds. These included farmers, hunter-gatherers, and office workers, who were compared to 72 monkeys scattered across zoos and sanctuaries.
A water change model for humans and chimpanzees with comparable lean body mass and body water pools.
Credit: Current Biology
The scientists calculated the water intake of each person in the study, whether from drinks or food. They also kept track of how much water was lost through urine, sweat, or the gastrointestinal tract. With all the numbers added together, it became clear that an average person’s body flows through about 3 liters of water every day. That’s about 12 cups. A chimpanzee or a gorilla passes twice as often.
The results were surprising because humans tend to sweat more than other primates. On a square centimeter of skin, “humans have ten times as many sweat glands as chimpanzees,” explains Pontzer. We can sweat about half a liter in a 30 minute workout. We also lead a much more active life than the monkeys at the zoo, with most monkeys only moving for a few hours a day, according to the scientists. So how come we use so much less water?
The researchers believe that the very real difference in water processing they observed in humans compared to other primates is related to evolutionary mechanisms. Our bodies had to adjust to need less water to stay healthy.
The scientists are now focused on figuring out exactly how this change happened. The data suggests that our sense of thirst was different from that of other monkey relatives. We just don’t want that much water. Notably, the water / calorie ratio is 25% less in human breast milk than in monkey milk.
It could also be that our nose has a lot to do with this. Fossils indicate that about 1.6 million years ago, with the emergence of Homo erectus, humans began to have more protruding noses than their evolutionary cousins. Gorillas and chimpanzees, on the other hand, have flatter noses.
What’s good about our noses? Since we tend to exhale water vapor, the nasal passages cool and condense it, making it liquid again. This fluid collects in the nose and is reabsorbed into the body. In essence, having a nose sticking out probably helped old people retain more moisture while breathing.
Read the study published in Current Biology.