The basis for terrestrial life in Aristotle’s biology is the nutritive process by which living things (plants and animals) produce and maintain their uniform parts and the organs made of these uniform parts. The nutritive process is thus extremely general, across all kinds. But it is also general in being present in all stages of the life cycle. Thus, it starts with the beginning of life, increases as the living thing grows, and subsides and is extinguished with the end of life. This variation in quantity is possible because there are two sides to the process, one is the heat necessary for “cooking” food into the parts of the living thing, and the other is the soul which informs this cooking. While the heat can be more or less, the soul is either there or not. The process of feeding (trephein) is shown to be Aristotle’s single sufficient and necessary condition for all natural life. It is the assimilation of food (trophê) to the living thing in question, an activity which the soul performs, thus producing and maintaining the living body, using the body’s heat as an instrument to work on food.