No part of me wants to go out there this morning. It is already 75 F and 0615. I'm late for my run on the hottest morning of the year. I have coffee and a slice of bread with peanut butter. I remember yesterday's 7 miler. To run like that is to completely embrace sweat. It runs down my entire body, stinging my eyes. It is an embrace of what humans evolved to be. We evolved sweat glands as we chased prey across the savanna. But upright, we have an advantage. With each gallop, our target's hind legs come forward together, compressing its abdominal cavity and pushing up against its diaphragm. This compresses the area available for the lungs to expand, hindering its inhalation. Humans, however, run unimpeded, with the additional benefit that we can carry weapons with our non-running limbs to make up for our lack of claws and teeth.
It is hot out there, in contrast to my dry home, cooled to a comfortable 76 F. But being cool and comfortable is not natural. It is not even healthy.