Human beings have grown large, energy-hungry brains, which require us to eat far more calories than our closest relatives. The same does not seem to hold up for the amount of water we get.
Compared to apes, a remarkable new study has found that our bodies mash through less moisture each day.
The researchers found that, on average, people consumed 3 liters, or about 12 cups, of water per day. On the other hand, zimpanzees, bonobos, and zoo-dwelling gorillas pass through nearly twice as much.
The results were something unexpected. Since humans have 10 times as much sweat glands as chimps, and are, on the whole, much more active than apes, you would expect us to lose more water each day, not less.
But even when accounting for outdoor temperature, body size and activity levels, people still needed less water to maintain a healthy balance.
“Compared to other apes, people in this study had significantly lower water conversion and consumed less water per unit of metabolic food energy,” the authors write.
This suggests that early hominins are somehow developing a way or means of maintaining their body filters, allowing them to travel from the rainforest to more acidic areas. It is not clear how this was achieved.
“Even being able to go a little further without water would have been a huge benefit as early humans began making a living in dry, savannah landscapes,” explained the study’s lead author and anthropologist mid- Herman Pontzer grew up from Duke University.
In the study, researchers monitored daily water turnover of 72 apes, in all zoos and rainforest sanctuaries, using double-labeled water containing deuterium and oxygen-18 as tractors. This was able to tell researchers how much water was obtained through food and drink and lost through excretion, urine, and the GI system.
The results were then compared to 309 people today who drank the same water with double labels. These people came from a range of lifestyles, including farmers, hunter-gatherers, and silent office workers.
Even among a small sample of adults in rural Ecuador, who drink a lot of water for cultural purposes (more than 9 liters per day for men and nearly 5 liters per day for women), the overall ratio was water to energy still matches people elsewhere, about 1.5 milliliters for every calorie consumed.
Indeed, it is worth noting that this same ratio is evident in human breast milk. On the other hand, onion breast milk has a water to energy ratio that is 25 percent lower.
These results show that the body’s thirsty response to the human body is ‘reconstituted’ over time, which means that we may want less water per calorie than our body’s counterparts. our ape grandchildren.
In the rainforest, apes get most of their water from plant foods, which means they can go days or weeks without drinking directly at all. People, however, cannot survive about three days without water, probably because our food is not so wet.
This inevitably requires us to drink alcohol more often than apes, which means we can’t stray too far from our connection to lakes and streams (or running water).
Pontzer refers to this as an ‘ecological leash’, and argues that natural selection has given people a longer direction so that we can travel farther without water, allowing hominins early expansion into drier environments where heat stress is greater and finding food requires more work.
However, there is another way our bodies can be modified to retain water. Unlike apes, humans have external nostrils, which are thought to reduce water loss when we breathe.
These obvious snores first appeared in the fossil record about 1.6 million years ago, when they appeared Homo erectus, and since then, noses have been so prominent that they have continued to move away from the flatter quartz.
More space inside nasal passages allows water to cool and condense, allowing water to recapture instead of expelling the liquid into the air. In addition to our thirsty response, these new noses may have been instrumental in allowing people to be more active in dry environments.
“Mystery remains to be solved, but clearly people are saving water,” Pontzer says.
“Finding out just how we do it is where we go, and that’s going to be a lot of fun.”
The study was published in Conventional biology.