A definition for “resource” reads: “a source of supply, support, or aid, esp. one held in reserve” (Webster's, 1996). In the context of biological organisms, this definition can be complemented in several ways. Resources of a certain type are more or less freely allocable for specific functions of the organism. As long as the functions serve an adaptive purpose, resource allocation does so as well. Because re-acquiring resources is almost always costly, natural selection gradually shapes organisms toward economic design. In biology, this principle of economization by natural selection is called “design for economy”, and it is thought to play an important part in evolutionary adaptation (Sibly and Calow, 1986; Diamond, 1993).
For example, energy is a typical resource. It is universal in the sense that almost every action of the organism, including passive maintenance of its state, requires energy. Plants typically have large and costly structures to acquire light, while many animals use most of their time in seeking food.
From another viewpoint, organisms maintain their life (homeostasis) by ranging from simple chemical loops to complex nervous systems. The former implicitly employs a very simple model of the environment, in which everything but a few parameters remain constant. On the other hand, organisms with large brains have a much richer picture of the world and relations of its constituents. Acting on the basis of complex causal relationships is much more efficient than simple momentary adaptation, because the outcomes of possible actions can be explicitly or implicitly predicted, sometimes to distant future.