In this theory of perfect natural adaptation, whether it be left to stand upon its old teleological basis, or be placed, as some modern investigators would place it, upon a genetic one, a very important factor has been left out, viz., the influence which plants exert upon one another. Adaptation, as the term is employed, is applied to a supposed correlation between the plant and its inorganic environment; and to this alone is attributed their entire local distribution. But facts of the class above considered prove that this is not only an inadequate explanation of such distribution, but that it is in many cases no explanation at all, since they so generally disregard inorganic conditions, and thrive equally well or better under entirely different ones from those which Nature furnished. Their distribution must, therefore, be almost entirely attributed to some other conditions; and to what other conditions are they subjected but to organic ones, to those which they reciprocally impose upon each other? It is to these organic conditions, then, to the mutual influence of different kinds of vegetation, growing, as it always does in a state of Nature, in close local proximity and contact, that we must look for the chief laws that control the local distribution of plants.
The modification, therefore, of the adaptation theory, or rather the substitute for it, which, in the light of these facts, I would propose might be called the law of mutual repulsion, by which every individual, to the extent of its influence, repels the approach of every other and seeks the sole possession and enjoyment of the inorganic conditions surrounding it—this mutual repulsion results at length in a statical condition which is always brought about through the action of the vital forces themselves, and which, as soon as reached, determines absolutely the exact place and degree of development of each species and each individual.
It is this statical condition which is apt to be lost sight of in the modern philosophy of evolution. The modification of species, the survival and advancement of some and the depauperating and extinction of others, all forms of variation and transmutation—these are dynamical phenomena, and only take place under the influence of disturbing agencies. Changes of this kind are slow and secular, and lie beyond the reach of direct observation, perceptible only to the eye of reason on the closest comparison of large masses of dependent facts. They, therefore, long escaped observation, and Nature remained until recent times a sealed book with respect to them. What wonder, then, that this still deeper and more occult law of biological statics should have remained still longer undetected, or only dimly seen? For, underlying this dynamical movement in organized beings, there must exist a universal statical condition throughout organic as throughout inorganic Nature.
The changes of which science has at length caught a glimpse can be nothing more than the regular and cyclical or fitful and spasmodic
