Political economists speak of the productiveness and prospectiveness of capital. We may well borrow these terms, using them in a somewhat modified sense. In our sense capital is productive in so far as it gives an immediate return; it is prospective in proportion as the return is expected largely in the future. A "pocket" may yield an immediate very large return of gold nuggets at a very slight expense of labor and appliances, but it is soon exhausted. In a mine the ore may be poor near the surface, but grow richer as the shaft deepens; the vein is narrow above, but widens below. The returns are at first small, its inexhaustible richness becomes apparent only after considerable time and labor. The value of the "pocket" is purely productive, that of the mine largely or purely prospective. Indeed it may be opened at a loss. But even a rich mine may be worked purely for its productive value; it may be "skinned." Let us apply this thought to the development of a species; although what is true of the species will generally be true of the individual also, for the development of the two is, in the main, parallel. In the animal all functions are to a certain extent productive, and all directly or indirectly prospective. When we examine the sequence of functions we cannot but notice how largely their value is prospective. As long as a lower function is rising to supremacy in the animal, it appears to be retained purely for its productive value; thus digestion in hydra or gastræa. But after a time animals appeared which had some muscle and nerve. And, by the process of natural selection, those animals which used digestion as an end for its productive value became food for, and gave place to, those using it as a means of supporting muscle and nerve of greater prospective value. And similarly, those animals which used muscle, or even mind, productively gave place to others using these prospectively. In other words, the functions and capacities of any animal, the extent of its conformity to environment, may be regarded as its capital. The animal may use this capital productively or prospectively. It may spend its income, and more too; it may increase its capital. Now social capital will always fall sooner or later to those communities whose members use it most prospectively, who are willing to forego, to quite an extent, present enjoyment, and look for future return. The same is true of all development. Sessile forms and mollusks, and, in a less degree, crabs and reptiles, worked for immediate return. They are like extravagant heirs who draw on their capital and sooner or later come to poverty. The primitive vertebrate, the mammal, and the other ancestors of man used their capital prospectively, and it increased, as if at compound interest.