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Re:Humans can't endure temperatures and humidities as high a... by dalbasal on Wednesday June 29, 2022 @08:09AM (#31919035)
It's interesting that many/most organisms are more sensitive to heat than cold. Cattle, dogs and whatnot usually enjoy room temperature, 20C-25C... like us. At 30-35, may will start to struggle. At 40-45, deaths start. Even heat adapted desert species need shade, burrows and such to survive 40+ temps.

Meanwhile, life at cold temperatures goes on. A lot of animals can adapt to a temperate 0C-20C conditions, and colder. Humans adapted and thrived, like many/most megafauna to pretty cold conditions. The far north has been inhabited by people for half a million years. You can get a lot further from comfort and still make it in the cold.

Heat is deadly.

Re:Humans can't endure temperatures and humidities as high a... by 323 on Wednesday June 29, 2022 @08:30AM (#31919227)
A body can burn energy to create heat. But it can't burn energy to remove heat.

That's a fundamental asymmetry.

Maybe it's also the reason why body core temperature is close to environment maximum temperature - since you can't really decrease your temperature you might as well learn to live at the upper extreme.

Re:Humans can't endure temperatures and humidities as high a... by chaorace on Wednesday June 29, 2022 @09:09AM (#31919590)
Indeed, it's why sweat was such an evolutionary leap for humankind. Our species didn't necessarily invent the sweat gland, but we certainly did become the sweatiest of the Great Apes -- by an order of magnitude in some measures.

I wonder how much of the species' worldwide dominance can be attributed to the evolutionary diceroll that placed our ancestors in subsaharan Africa? Could we have survived in Egypt, Mesopotamia, or India without sweat?

Re:Humans can't endure temperatures and humidities as high a... by dalbasal on Wednesday June 29, 2022 @09:21AM (#31919716)
In the sweatiest of those places, our sweaty strategy is imperfect.

Sweating works well in dry climates, not as well in humid ones. In high enough humidity, the sweat doesn't evaporate, doesn't cool you, and the whole system becomes a moist, messy loop.

In dry, hot climates sweating works well, but increases our water consumption... these are the habitats where water is often scarce.

Tradeoffs.

Re:Humans can't endure temperatures and humidities as high a... by acoard on Wednesday June 29, 2022 @11:16AM (#31921380)
Are there better natural responses to heat that we see in mammals?

I know sweating isn't perfect, for the reasons you mentioned, but do we see nature evolving any better solutions at a mammalian level?

My armchair understanding is sweating is a natural marvel with nothing else like it seen in creatures as large as us. That it truly is a differentiator between humans and other animals (or mammals at least). Sweating is the foundation of humans ability to engage in long-distance endurance running which is one of our unique features, also called persistence hunting[0]. You can easily draw a line between this sweating and our ability to travel large distances and hunt the way we did, which in turn can be connected to humanity's success as a species on earth.

[0] https://en.wikipedia.org/wiki/Persistence_hunting

Re:Humans can't endure temperatures and humidities as high a... by dalbasal on Wednesday June 29, 2022 @12:41PM (#31922559)
All true, and impressive considering that we recently evolved from tree dwelling primates but... There are plenty of animals adapted to heat, and can perform similar feats.

African wild dogs, dingos and other canines can persistent hunt in similar hot conditions. They're much faster than us, so it's not as extreme a strategy as human "track and spook" methods... but arguably better.

Elephants manage to carry those huge, heat retaining bodies. Our Savannah nurseries are full of megafauna like us that live in these conditions effectively.

Re:Humans can't endure temperatures and humidities as high a... by 323 on Wednesday June 29, 2022 @11:27AM (#31921531)
In general there is no single reason for our success.

Some argue sweating, others that we outsourced digestion (fire cooked food), others that we are bipedal, ... not to mention later stuff like language/intelligence.

Re:Humans can't endure temperatures and humidities as high a... by Tagbert on Wednesday June 29, 2022 @10:48AM (#31920916)
And it was evolved for the African savanna which is relatively dry. We already had enhanced sweating by the time we moved into more humid locales.
Re:Humans can't endure temperatures and humidities as high a... by drew55555 on Wednesday June 29, 2022 @10:07AM (#31920308)
I wonder if dogs would still be a popular pet if they sweat like people.
Re:Humans can't endure temperatures and humidities as high a... by staplung on Wednesday June 29, 2022 @10:55AM (#31921050)
Horses also sweat. We don't seem to be too bothered by it (although I cannot claim to know what a sweaty horse smells like).

Also, cats and dogs do sweat a little, mostly through their paws.

Re:Humans can't endure temperatures and humidities as high a... by cwillu on Wednesday June 29, 2022 @10:04PM (#31927999)
Fun fact: part of the scary-effective logistics of the mongols was curing fresh meat into jerky using horse sweat during the ride.
Re:Humans can't endure temperatures and humidities as high a... by mrtranscendence on Wednesday June 29, 2022 @10:46AM (#31920895)
You ever smell a dog after she's been playing hard in the sun for a half hour? It doesn't last that long, but they can get a bit fragrant.
Re:Humans can't endure temperatures and humidities as high a... by Cerium on Wednesday June 29, 2022 @10:16AM (#31920438)
I have known some dogs that drool more than any person can sweat.
Re:Humans can't endure temperatures and humidities as high a... by titzer on Wednesday June 29, 2022 @09:38AM (#31919943)
Heatpumps are a thing, it's just that evolution never stumbled on them.
Re:Humans can't endure temperatures and humidities as high a... by mmastrac on Wednesday June 29, 2022 @10:10AM (#31920347)
Evolution seems to prefer proteins that denature at higher temps instead:

https://en.wikipedia.org/wiki/Hyperthermophile

Re:Humans can't endure temperatures and humidities as high a... by laci37 on Wednesday June 29, 2022 @09:49AM (#31920073)
I don't think there are any coolants that would be appropriate for life's temperature ranges at the right pressures that can be synthesized biochemically.
Re:Humans can't endure temperatures and humidities as high a... by 323 on Wednesday June 29, 2022 @09:58AM (#31920173)
People are working on propane biochemical synthesis: https://pubmed.ncbi.nlm.nih.gov/25181600/

I don't know about the other part (temperature/pressure).

Re:Humans can't endure temperatures and humidities as high a... by warble on Wednesday June 29, 2022 @01:55PM (#31923548)
Sweat is an open heatpump loop. You're intending a closed loop of course in your comment, but same process.
Re:Humans can't endure temperatures and humidities as high a... by titzer on Wednesday June 29, 2022 @03:51PM (#31924926)
It isn't though, because powered mechanical compression and decompression is what allows a heat pump to outperform the inherent thermodynamic limit of evaporative cooling.
Re:Humans can't endure temperatures and humidities as high a... by eternityforest on Wednesday June 29, 2022 @04:35PM (#31925408)
Is that possible? Could there be a biochemical equivalent of a Peltier junction?
Re:Humans can't endure temperatures and humidities as high a... by bicolao on Wednesday June 29, 2022 @10:57AM (#31921071)
> since you can't really decrease your temperature you might as well learn to live at the upper extreme

There is a MinuteEarth video about this YouTube if I remember correctly and the reason is well.. more reasonable. Our body works better at higher temperature, but of course if it gets too high everything breaks down. So the optimum temp is somewhere closer to the upper limit.

Re:Humans can't endure temperatures and humidities as high a... by dalbasal on Wednesday June 29, 2022 @09:15AM (#31919658)
Hah. Interesting point that I hadn't thought of at all. Very simple.
Re:Humans can't endure temperatures and humidities as high a... by tialaramex on Wednesday June 29, 2022 @08:27AM (#31919206)
Almost (?) all life runs off chemical reactions that are temperature sensitive and produce heat. In a closed system these reactions stop, they are able to continue (and so life continues) only within a context where the heat is lost.

You can adjust the gradient so as to change the rate of heat loss, you can grow fur, shunt blood flow away from outer surfaces - or the reverse. Humans have clothes and even buildings to do this even more. Say you're losing 10K per hour and producing 5K per hour, if you cut the gradient to 50% you break even and your temperature remains viable indefinitely.

But that only works when you're losing heat. If you can't lose heat, this doesn't help. You will die.

Re:Humans can't endure temperatures and humidities as high a... by jcranmer on Wednesday June 29, 2022 @09:54AM (#31920123)
The human body needs to maintain core body temperature at 37°C. Whenever we extract energy from our food to do stuff, some of that energy gets dumped into heat. If we assume (just for round numbers) that we eat 2000 Calories/day, and that 10% of that energy is heat, then that's 200 Calories/day of heat that needs to be dumped into our environment. Abusing units somewhat, if a human being is 100 kg of mostly water, that's 2°C/day of heat. If we didn't dump that heat, in a day, core body temperature rises to 39°C and we get heatstroke.

Heat naturally flows from hot to cold at a rate proportional to the difference in temperature. If we're fully passively cooled at an environmental temperature 25°C at a rate of 2°C/day, then at 1°C, we'd be passively cooled at 6°C/day. However, we can also modulate heat flow by introducing some thermally nonconductive layers--or, in layman's terms, put on a sweater. When it's cold, all you have to do is slow down the rate of heat flow.

But hotter temps are more difficult. We can't take off thermal insulators or modulate the main thermal barrier between core body temperature and the outside world (i.e., skin). At 31°C, passive cooling is down to 1°C/day, and we need to turn to active cooling. Sweating is the main mechanism for humans: it takes heat for liquid water to become water vapor, and this heat is drawn from your skin surface, cooling it (this kind of allows heat to move from a colder to a hotter environment, unlike passive cooling). At 37°C, there's no longer any passive cooling, and active cooling needs to handle 2°C/day.

But hotter than that, and things get worse: the environment is now passively warming you up. By 43°C, that's now 3°C/day of heat that needs to shed, and 49°C ups it to 4°C/day. At some point, you're going to overwhelm the ability of active cooling to cool you down, and the passive heating is still going to warm you up even if you shut down metabolism. Even worse is if sweating isn't effective at cooling down--at high humidities, the sweat won't evaporate and the cooling effect won't happen. (This also illustrates why heat-and-humidity can be deadly even at below-body-temperature environments.)

This analysis was purely done for humans, but it's pretty similar for most organisms, just with different set points for core body temperature and active cooling mechanisms. Fundamentally, extreme cold is "easy" to handle--just slow down heat loss; extreme heat requires developing ways of pumping heat from a hot reservoir to a cold reservoir, which thermodynamics does not look kindly on.

Re:Humans can't endure temperatures and humidities as high a... by krzat on Wednesday June 29, 2022 @08:11AM (#31919047)
Well it's easier to make fire than a fridge.
Re:Humans can't endure temperatures and humidities as high a... by wongarsu on Wednesday June 29, 2022 @08:26AM (#31919200)
And you can insulate from cold with fat, but insulating against heat is difficult because you have to get rid of the waste heat from muscles and other body functions somehow.
Re:Humans can't endure temperatures and humidities as high a... by racl101 on Wednesday June 29, 2022 @10:35AM (#31920721)
You can put on a sweater to sleep on a very cold night.

But you can't take off your skin to sleep on a very hot night.

Re:Humans can't endure temperatures and humidities as high a... by dorgo on Wednesday June 29, 2022 @11:50AM (#31921866)
I don't see how a naked human can survice 0C for long. Maybe our gear and technology is better suited for cold temperatures.

All in all I would say the temperature tolerance is the same in both directions.

Re:Humans can't endure temperatures and humidities as high a... by warble on Wednesday June 29, 2022 @01:58PM (#31923589)
0C is pretty cold, but the Yaghan indians seemed to handle it, or close to it, basically naked:

https://www.ancientpages.com/2016/09/19/mystery-yaghan-peopl...

Re:Humans can't endure temperatures and humidities as high a... by swayvil on Wednesday June 29, 2022 @09:02AM (#31919529)
You see it working outside (building fences or whatever). You can work all day in the cold but heat cuts your day in half. It drains your energy.
Re:Humans can't endure temperatures and humidities as high a... by amelius on Wednesday June 29, 2022 @08:36AM (#31919294)
Makes sense, given that people often store biological specimens at -80C, not at +50C.
Re:Humans can't endure temperatures and humidities as high a... by codewritero on Wednesday June 29, 2022 @08:26AM (#31919191)
It wasn’t that long ago that an article making the exact opposite point was at the top of this site.
Re:Humans can't endure temperatures and humidities as high a... by dalbasal on Wednesday June 29, 2022 @08:30AM (#31919237)
got link?
Re:Humans can't endure temperatures and humidities as high a... by codewritero on Wednesday June 29, 2022 @09:46AM (#31920025)
Can’t find it. The title was along the lines of global warming might result in a net increase in usable land.
Re:Humans can't endure temperatures and humidities as high a... by kjs3 on Wednesday June 29, 2022 @10:28AM (#31920606)
How is "land which is too cold to use now might be useable on a warmer world" and "human beings aren't as tolerant to higher heat as we once thought" the 'exact opposite' of each other?
Re:Humans can't endure temperatures and humidities as high a... by schoen on Wednesday June 29, 2022 @10:23AM (#31920547)
Well, it might!

It might also be necessary for many people to migrate to cooler areas than where they currently live.

Re:Humans can't endure temperatures and humidities as high a... by namlem on Wednesday June 29, 2022 @10:50AM (#31920958)
While I suspect this is probably not true, it is plausible due to the fact that there is a lot of land in the northernmost regions of the world.