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Comment by doc4t | Hacker News Reader

A horse can't sweat (at least not enought to reduce body temp. sufficiently) and thus can only get rid of the heat through breathing. Eventually it will overheat and either rest or die.

Humans don't suffer from this limitation. If you're curious I suggest you read Born To Run

http://www.amazon.co.uk/Born-Run-Hidden-Ultra-Runners-Greate...

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Where does the phrase "Sweating like a horse" come from then?

And I've often heard people complaining that training horses in hot weather is horrible because they get sweaty and all the dust sticks to them.

While I have never myself witnessed a horse sweat, I've read/heard enough references to the sweatines of horses that I assume horses do in fact ... sweat.

They key is "not efficiently enough". The body volume (where heat is produced) is propoprtional to the cube of linear dimensions, when surface area is proportional only to the square — hence the bigger you are the harder it is to get read of extra heat. And vice versa: the smaller you are the more effort it takes to keep yourself warm.

> (...) get read of extra heat.

rid

There's a tool for grooming horses called a "sweat scrapper" for a reason. :)

If you ever watch a horse race or any other time a horse is working hard and fast, you'll see white foam near where the reins touch the horse's neck and and anywhere else there's friction. That's frothed up sweat.

Horses absolutely do sweat.... however, this is where the bipedal aspect comes into play.

Not only is a bipedal gait more efficient over long distances, but the fact that humans have a mostly hairless torso which is directly perpendicular to the direction they are running means two things: a maximum amount of surface area of sweaty skin is being exposed to moving air vs. body mass it has to cool. Much greater than a quadraped's.

I think the BBC 'Origins of us' series covered this in an episode also. They conclude that where humans evolved from in Africa changed from being lush forest to grassy plains at one time. We as a result had to evolve to catch prey and as there was nowhere to hide, we had to out-run the prey, hence no hair and sweating.

Wikipedia says horses do sweat.

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