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Beating the Summer Heat — Thanks to Human Exceptionalism

David Klinghoffer

It’s hot out. While this is fueling fears about how “Climate change is supercharging a hot and dangerous summer,” with “Heatwaves from the Arctic to Japan,” be glad that you’re a human being, and not some other kind of mammal.

I enjoy University of Washington climatologist Cliff Mass and his blogging on local weather and more. He commented the other day on the fact that Seattle has fewer air conditioners per capita than any other big city. That’s a tribute to the lower summer temperatures in our area but also to the fact that the summer air here is dry (contrary to the stereotype). He notes the interesting fact about human beings that dry air is comfortable for us when it’s hot. Why?

Humans are unique in our ability to sweat from our skin. No other mammal other than horse[s] can do so effectively….and according to what I read, horses sweat differently than us (mainly in their armpit area)…. With millions of sweat glands and naked skin…..we are the superstars of sweat. And evaporation of water requires huge amounts of energy (heat), and thus is an enormously effective cooling mechanism.

His takeaway has to do with the pleasant climate we enjoy, but Professor Mass has actually hit on a point made by Discovery Institute biologist Michael Denton. 

Privileged Species

Denton shows how chemistry, physics, and biology work together in a way reflecting a design that appears to have had us in mind. From the video Privileged Species:

[Denton:] The evaporative cooling of water is one of the greatest of any fluid that’s known.

[Narrator:] The human metabolism produces large amounts of heat that needs to be discharged or the body will overheat and die. The evaporation of water through perspiration is one of the key ways our body gets rid of excess heat. Water is especially fit for the task of cooling us because it absorbs a large amount of heat when it evaporates. 

In fact more heat is absorbed by the evaporation of water than by the evaporation of almost any other known fluid at ambient temperatures and pressures. 

Water is uniquely suited to help us shed excess heat in hot climates. When the outside temperatures exceed the level of your body temperature, other ways of getting rid of heat won’t work. 

[Denton:] Because the only way to lose heat when the environment around you is reaching 38 degrees centigrade is by evaporative cooling, because you can’t radiate the heat out because the environment is 38 degrees, warmer than you. So it’s absolutely critical to warm-blooded organisms like ourselves that the evaporative cooling of water is very high. It’s one of the highest of any common fluids.

[Narrator:] The high evaporative cooling of water appears to benefit humans more than any other animal. Being relatively hairless, humans lose heat through evaporative cooling more efficiently than any other mammal. Consequently in the heat of the day, humans can exert themselves continuously for longer periods of time than other mammals.

This is not something that Denton is alone is noticing. 

An Abundance of Eccrine Glands

From Scientific American:

Fur-covered mammals forced to exercise energetically or for prolonged periods in the heat of day will collapse from heat exhaustion.

Humans, in addition to lacking fur, possess an extraordinary number of eccrine glands — between two million and five million — that can produce up to 12 liters of thin, watery sweat a day. Eccrine glands do not cluster near hair follicles; instead they reside relatively close to the surface of the skin and discharge sweat through tiny pores. This combination of naked skin and watery sweat that sits directly atop it rather than collecting in the fur allows humans to eliminate excess heat very efficiently. In fact, according to a 2007 paper in Sports Medicine by Daniel E. Lieberman of Harvard University and Dennis M. Bramble of the University of Utah, our cooling system is so superior that in a marathon on a hot day, a human could outcompete a horse.

“Outcompete a horse”…what’s that you say about humans and our “unintelligent design”? Denton’s insight is that nature appears to be specially designed for creatures like us. That’s a cool thought. Enjoy your summer weekend!