Our body’s thousands of specialized proteins, such as the actin and myosin that make up the molecular gadgetry of our muscles, can do their jobs because of their precise three-dimensional shapes. Warm those proteins just a few notches above 98.6 degrees and the chemical fasteners maintaining these shapes begin to loosen and the proteins can’t function properly. Heat those proteins to, say, 106 or higher, and they can’t hold it together at all. If the proteins in the brain cells that help regulate breathing reach such temperatures, for example, you’ll stop breathing.
Luckily, evolution has come up with some basic, commonsense coping mechanisms. For animals known as Washingtonians, this almost always means seeking air conditioning. (This is common sense as long as you ignore the climate-changing consequences.) Small animals with big enough tails, such as the Cape ground squirrel of southern Africa, can sometimes use their rear appendage like a parasol. A standard hippo option is to bask in cool river water.
But in places where it’s boiling hot in the shade for days, months or even longer, some resourceful animals resort to estivation, the hot-climate version of hibernation. One of the most extreme estivators is the lungfish, according to Gregory Florant, a zoologist at Colorado State University in Fort Collins.
Several species of African lungfish, eellike creatures with lungs that enable them to breathe air when there isn’t enough oxygenated water around, live in habitats where heat can be scorching and moisture can be minimal even for years. “Lungfish burrow in the mud, secrete a crusty mucus cocoon around themselves and drastically lower their metabolism until conditions are better for them to move around,” Florant explains. Gross and boring, yes, but effective.
Moving into shade, migrating to more temperate places and basking in the sun are behavioral tactics animals use for maintaining their cool. But they also have an array of physiological tools to manage the heat. The most familiar of these involves taking advantage of the cooling effect of evaporating water — in other words, sweating.
When the body begins to heat up, an ingenious system of temperature sensors informs the thermoregulation centers in the brain that orchestrate the body’s couple of million sweat glands. The sweat that is produced absorbs body heat as it vaporizes and dissipates, thereby keeping your body temperature close to your normal set point.
Horses, humans, donkeys and other beasts of burden are champion sweaters, which is one reason they are so good at exerting themselves for long periods of time. Those basking hippos also are famous for a sweat that is red, and a team of Japanese chemists discovered that the sweat has antibiotic and sunblocking characteristics, which might trump any role it plays in cooling.
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