Scientific American: Human Evolution Led to an Extreme Thirst for Water

Learned something new today! This is a really cool dive into needing water. It never really occurred to me…but other primates don’t make New Years Resolutions to drink a gallon of water every day. :rofl: Is this how we are unique?

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" A recent study by Daniel Aldea of the University of Pennsylvania and his colleagues found that repeated mutations of a gene called Engrailed 1 may have led to this abundance of eccrine sweat glands." Hey, I know that paper – I’m one of the authors.

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Fascinating article. As an older guy, I am more aware of how much I drink, sweat, and urinate. You need to keep that urine light yellow to avoid kidney stones, but too much and you are up all night.

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That was a very interesting read. I remember watching a nature documentary about some desert animals whose only source of water was a particular type of plant root… and thought it was amazing since there’s no way humans could survive like that!

It reminds me of reading Antoine de Saint Exupery’s account of how he almost died of thirst after crash-landing in the desert. He compared water to an umbilical cord:

“We believe that man is free. We never see the cord that binds him to wells and fountains, that umbilical cord by which he is tied to the womb of the world. Let man take but one step too many … and the the cord snaps.”

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Congratulations, Steve @glipsnort
!
To understand how water has influenced the course of human evolution, we need to page back to a pivotal chapter of our prehistory. Between around three million and two million years ago, the climate in Africa, where hominins (members of the human family) first evolved, became drier. During this interval, the early hominin genus Australopithecus gave way to our own genus, Homo . In the course of this transition, body proportions changed: whereas australopithecines were short and stocky, Homo had a taller, slimmer build with more surface area. These changes reduced our ancestors’ exposure to solar radiation while allowing for greater exposure to wind, which increased their ability to dissipate heat, making them more water-efficient.

Other key adaptations accompanied this shift in body plan. As climate change replaced forests with grasslands, and early hominins became more proficient at traveling on two legs in open environments, they lost their body hair and developed more sweat glands. These adaptations increased our ancestors’ ability to unload excess heat and thus maintain a safe body temperature while moving, as work by Nina Jablonski of Pennsylvania State University and Peter Wheeler of Liverpool John Moores University in England has shown.

Sweat glands are a crucial part of our story. Mammals have three types of sweat glands: apocrine, sebaceous and eccrine. The eccrine glands mobilize the water and electrolytes inside cells to produce sweat. Humans have more eccrine sweat glands than any other primate. A recent study by Daniel Aldea of the University of Pennsylvania and his colleagues found that repeated mutations of a gene called Engrailed 1 may have led to this abundance of eccrine sweat glands. In relatively dry environments akin to the ones early hominins evolved in, the evaporation of sweat cools the skin and blood vessels, which, in turn, cools the body’s core.

Armed with this powerful cooling system, early humans could afford to be more active than other primates. In fact, some researchers think that persistence hunting—running an animal down until it overheats—may have been an important foraging strategy for our ancestors, one they could not have pursued if they did not have a means to avoid overheating…

Please how the article points out that climate and ecological change led to the development of sweat glands, not that sweat glands led to climate change.

This does not mean that living things can will evolutionary changes, but that mutations that would not have been “selected in” in humid conditions, were selected in during the dry conditions when hominids were becoming bipedal, which of course is another adaption to the environment. Also that this adaption was very positive in giving humans control over the environment.

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