It Takes Energy to Get Energy

Abstract

Imagine you are a prehistoric hunter-gatherer. Your primary motivation is to find food, as that is your only source of the energy which your body needs to stay alive and without it you will slowly starve and die. The balance between the amount of food energy gained in hunting and gathering, and the amount of energy expended in those activities is critical. If that ratio is not high enough you will still die from starvation, just more slowly than if you had no food at all. Let us say that for every usable calorie of energy you gain, you expend 1 calorie in the hunting and gathering process. Then you would be fine, would you not? Unfortunately not, as you would still starve to death, just even more slowly. Your body has a whole host of functions which are not directly related to finding food but critical to your survival. First of all, there is the need for water, without which you will die in about 5–10 days. Then, you have to digest the food, to transform it into useful calories, and you have to excrete the processed food and water otherwise your bladder and intestines would swell up rendering you painfully immobile. So, let us say all these other functions require a doubling of calorific intake, so you now get 2 calories for every calorie spent hunting and gathering. Now you are good, right? Still the answer is no as the human body also has the annoying need to sleep for approximately one third of the day otherwise you will slowly malfunction and start going somewhat mad. So, let us add another calorie for that. Therefore, 3 calories gained for every calorie spent in hunting and gathering make for a good balance.