Walden (part 1) Henry David Thoreau

By the words, necessary of life, I mean whatever, of all that man obtains by his own exertions, has been from the first, or from long use has become, so important to human life that few, if any, whether from savageness, or poverty, or philosophy, ever attempt to do without it. To many creatures there is in this sense but one necessary of life, Food. To the bison of the prairie it is a few inches of palatable grass, with water to drink; unless he seeks the Shelter of the forest or the mountain's shadow. None of the brute creation requires more than Food and Shelter. The necessaries of life for man in this climate may, accurately enough, be distributed under the several heads of Food, Shelter, Clothing, and Fuel; for not till we have secured these are we prepared to entertain the true problems of life with freedom and a prospect of success. Man has invented, not only houses, but clothes and cooked food; and possibly from the accidental discovery of the warmth of fire, and the consequent use of it, at first a luxury, arose the present necessity to sit by it. We observe cats and dogs acquiring the same second nature. By proper Shelter and Clothing we legitimately retain our own internal heat; but with an excess of these, or of Fuel, that is, with an external heat greater than our own internal, may not cookery properly be said to begin? Darwin, the naturalist, says of the inhabitants of Tierra del Fuego, that while his own party, who were well clothed and sitting close to a fire, were far from too warm, these naked savages, who were farther off, were observed, to his great surprise, "to be streaming with perspiration at undergoing such a roasting." So, we are told, the New Hollander goes naked with impunity, while the European shivers in his clothes. Is it impossible to combine the hardiness of these savages with the intellectualness of the civilized man? According to Liebig, man's body is a stove, and food the fuel which keeps up the internal combustion in the lungs. In cold weather we eat more, in warm less. The animal heat is the result of a slow combustion, and disease and death take place when this is too rapid; or for want of fuel, or from some defect in the draught, the fire goes out. Of course the vital heat is not to be confounded with fire; but so much for analogy. It appears, therefore, from the above list, that the expression, animal life, is nearly synonymous with the expression, animal heat; for while Food may be regarded as the Fuel which keeps up the fire within us—and Fuel serves only to prepare that Food or to increase the warmth of our bodies by addition from without—Shelter and Clothing also serve only to retain the heat thus generated and absorbed.

The grand necessity, then, for our bodies, is to keep warm, to keep the vital heat in us. What pains we accordingly take, not only with our Food, and Clothing, and Shelter, but with our beds, which are our night-clothes, robbing the nests and breasts of birds to prepare this shelter within a shelter, as the mole has its bed of grass and leaves at the end of its burrow! The poor man is wont to complain that this is a cold world; and to cold, no less physical than social, we refer directly a great part of our ails. The summer, in some climates, makes possible to man a sort of Elysian life. Fuel, except to cook his Food, is then unnecessary; the sun is his fire, and many of the fruits are sufficiently cooked by its rays; while Food generally is more various, and more easily obtained, and Clothing and Shelter are wholly or half unnecessary. At the present day, and in this country, as I find by my own experience, a few implements, a knife, an axe, a spade, a wheelbarrow, etc., and for the studious, lamplight, stationery, and access to a few books, rank next to necessaries, and can all be obtained at a trifling cost. Yet some, not wise, go to the other side of the globe, to barbarous and unhealthy regions, and devote themselves to trade for ten or twenty years, in order that they may live—that is, keep comfortably warm—and die in New England at last. The luxuriously rich are not simply kept comfortably warm, but unnaturally hot; as I implied before, they are cooked, of course à la mode.

Thoreau is amazingly accurate in his allegory of food being the fuel of life. It is, as everyone knows, where we get our energy from, but maybe the realization that food is literally fuel is lost on some people. If you take a lighter and hold it to a nice oily nut like a brazil nut or a walnut, it will just burn like a sooty candle. Doritos and dry spaghetti and just about any food that isn’t filled with water will burn. It’s no coincidence that the amount of heat given off burning an almond is the same as the amount of heat that your body can generate by metabolizing it. It’s also no coincidence that carbon dioxide is the chemical byproduct of both reactions.

We use little molecular machines to accomplish all of the chemistry that our body needs. If you think about a fish in the ocean, the chemical environment inside the fish is very (and obviously) different than the chemical environment outside the fish. Most of the little reactions that take place in any plant or animal that keep their chemistry just right for their own bodies are facilitated by the little molecular machines, or enzymes. You’ve heard the term for these machines before but you might not know what they did. Enzymes are used for all kinds of different tasks of chemical housekeeping in our bodies, and each task has a unique type of enzyme assigned to it.

Enzymes, like any machine, operate best in a certain temperature range. Your car doesn’t get very good mileage until the engine warms up, but if it gets too hot, it might leave you stranded on the side of the road. Enzymes are the same way. They don’t work very efficiently when they are cold, and if they get too hot, they break down all together. “Cold blooded” animals get most of their body heat from the environment, and that’s why you’ll see snakes and lizards sunning themselves on the rocks. All that warmth gives a their enzymes a boost in efficiency, and gets their body’s chemistry back in order. With cold, inefficient enzymes, those lizards and snakes would soon be up to their ears in a backlog of chemical chores that needed to be carried out. Cold blooded animals that don’t have a chance to warm up in the sun, like cold water fish, have evolved to have enzymes that have their most efficient temperature much lower. This is a good arrangement so long as the fish don’t find themselves in literal, and figurative hot water.

Fortunately for the sake of ice hockey leagues everywhere, your ancestors evolved a body chemistry that produced enough heat to keep enough your enzymes at a consistent and toasty warm temperature. It takes a lot more food to keep up all that body temperature, but it allows you to run long distances, and get up and be active early in the morning before the sun warms you up. I guess caffeine helps with that too.