Did Sweating Evolve To Keep Us Cool Or Expell Excess Salt?

I've yet to break out in a sweat after eating sardines and sea-food. Once I ate so much salt water crab, I'm talking all you can eat. I sat there and ate and ate and ate more than I have ever eaten EVER. With a buddy and beer of course. Like 6 hours of eating crab! I Was sooo thirsty you couldn't believe it - for like 8 hours I was drinking water (I think I was half salt!). Don't remember breaking out in a sweat!

Anyway, in physiology class we ran experiments on Ss drinking varying levels of salt water and the DRAMATIC effects it has on urine and kidney function - no one breaks out in sweat.

 

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Sweat is a very effective coolant in dry and cold conditions, and as you point out less effective in humid conditions - such as near the ocean.

It's more common inland, where there are ponds and lakes and such not salt-contaminated.

For every river on the coast, there are two or three along a parallel transect miles inland - all the tributaries, etc.

I'm not saying that humans didn't evolve on the beach - I sort of think they probably did, in part - just that sweating as they do, an adaptation best suited to exertion in the heat of the day far from cooling factors such as ocean water, seems unlikely to be an adaptation for the beach environment.

 

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You're definitely wrong on this point. The heat can escape from the body if sweat is simply wiped off. It DOESN'T have to evaporate.

The proposed evolution would have taken place in the vast Congo estuary, so there wouldn't need to be any travel to find fresh water. The other point which everyone seems to miss is that the ancestors I am talking about would have existed tens of millions of years ago, plenty of time for genetic mutations to alter the excess salt system of the body!!

 

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Your blood is ~0.9mg/dl salt (Na more than any other ion). Your sweat is a reflection of your blood and is ~.45mg/dl saline. It would take extra work to distill your blood essentially, and expel a salt-free solution. The homeostasis involved for regulating salt is almost entirely handled by your kidneys. Considering the physiology, it's not a logical conclusion to say that sweating evolved to handle salt disposal instead of regulate heat. As far as I know, having a negative salt balance will not directly turn off the sweat mechanism as you'd expect if the system is in part designed to regulate salt balance.

 

As the sweat was already at body temperature in your body, wiping it away does not affect the temperature of your body!

It's basic calorimetry.

The only non-evaporation method by which sweat can lower your body temperature, is due to wet skin being more conductive to heat than dry skin, BUT as this requires airflow to transport away the heat (it's lost through convection, essentially, not radiation) the air causes evaporation, and the amount of heat lost by convection alone is tiny when compared to evaporation.

 

What about a combination of heat and salt regulation? The move away from the estuary to the plains would have reduced the salt balance problem and so changed the body's physiology.

My brother and I had this conversation years ago when he was marathon running. The athletic magazines say that wiping sweat away DOES aid heat loss. Simple common sense from personal experience would also confirm this. The action of wiping will remove the warm sweat, allowing more to replace it. The movement will also stimulate air convection. I agree that you can't beat a cooling sea breeze though.

 

Wiping away sweat does nothing to lower your body temperature. Drinking cooler water to replace the sweat will reduce your body temperate.

How does that make common sense to you? The fluid in your body, that is expressed as sweat, is at body temperate before you sweat it out. Does your body cool when you take a pee? No, because the pee you lose is at the same temperature as your body. If you have 1 litre of water at 37degC, and pour half into another container, you end up with two 500cc containers of water, at 37degC. Taking some away does not lower the temperature of either.

Wiping sweat away will not aid convection. Just having wet skin does that.

 

The sweat must be a higher temperature than the body´s core temperature. It is the same principle as the blood vessels dilating to allow more warm blood to reach the skin surface, which happens when we blush, for example.

 

How does sweat achieve a higher temperature than the body? Are you saying the body pushes heat into sweat? LOL !

Blood vessels dilating allows more blood to flow to the surface to be cooled.

You are clearly confused about several mechanisms.

 

So why does wiping sweat away in the gym make me feel cooler? You´re saying that it´s my imagination?

 

So you don´t think that the sweat can be a higher temperature than the body´s core temp? If so then my brother and/or the athletics magazine must have made a mistake. Isn´t the dilated blood vessels carrying blood which is of a higher temperature than the body´s core though?

edit - thinking about it, the blood and sweat only need to be warm to release heat from the body. Warm sweat which is wiped off will rid the body of the small amount of heat that the sweat contains.

The main point of early humanoid evolution occurring within the Congo delta still stands; the idea of excessive sweating to get rid of excess salt is still a logical possibility. I propose that early humans and horses evolved in similar estuarine environments. How much this idea goes against the mainstream view I don´t know. It makes sense to me.

 

Ask yourself this, how could extra heat get into the sweat? It can't. Sweat is at the same temperature as the body, period.

What did the magazine actually say?

No. Dilated blood vessels allow a larger volume of blood to be cooled. That's it.

You still don't seem grasp the fundamentals of calorimetry. It's not losing anything that cools the body. You could cut your arm off, and remain the same temperature!

Sweat cools you via evaporation, using the heat from the body to change state from liquid to vapour.

Like I said, taking a pee doesn't cool you, but you are losing warm fluid, so sweating, and losing warm fluid is not a mechanism via which you lower your temperature either.

The main point of early humanoid evolution occurring within the Congo delta still stands; the idea of excessive sweating to get rid of excess salt is still a logical possibility. I propose that early humans and horses evolved in similar estuarine environments. How much this idea goes against the mainstream view I don´t know. It makes sense to me.[/QUOTE]

 

I'm not overly interested anymore about this small point. You seem to have misquoted or something at the end; I believe the main idea is still a possibility.

 

It's not a 'small' point, it's the crux of calorimetry, and shows you don't grasp basic science. All conclusions you draw therefore, are based on incorrect assumptions, and equally incorrect.

 

Can you name any other animals apart from humans and horses which use the profuse sweating mechanism for cooling? Do you accept that this mechanism requires a substantial intake of water, so making it a poor mechanism in arid environments? Do you accept that the muscular heat produced in activity in cold environments still produces profuse sweating which can be potentially fatal due to it freezing? Do you accept that profuse sweating is a poor mechanism in humid environments? Can your brain make the connection that humans and horses are both naturally suited to coastal and esturine environments? In short, are you able to perform any kind of lateral thinking, or are you so sure of yourself that you can only repeat what you've been taught?

 

common sense do you actually HAVE any common sense?

yes sweating is tired to sympathetic activation, it may or may not be a good idea depending on the situation. However its DEFINITLY NOT A SELECTIVE MECHANISIUM FOR EXPELLING SALT. i mean are you a compleate moron, its not even ISOTONIC let alone hypertonic. Not to mention that it cant select WHICH electroylites its going to expell, it expells them ALL.

The ONLY organ which can selectivly expell ions and expell them at a greater concentration than blood are the kidneys. Now go away and do some BASIC anat and phys classes

 

I dont mean to state the obvious, but this seems similar to that idiotic question "do fish get thirsty?"

 

That idea exists only in your head. I feel sorry for that idea, being trapped in there, with you.

 

lol