WHAT IS EVOLUTION? 723 



and reaction, co-operate to produce climates and physical conditions 

 such as we now find them. This is physical geography. Or, we may 

 study the earth in its gradual progress toward its present condition 

 the changes which have taken place in all these parts, and consequent 

 changes in climate ; in a word, the gradual process of becoming what 

 it now is. This is physical geology it is evolution. 5. Lastly, we 

 may study the whole organic kingdom in its entirety as we now find 

 it the mutual relation of different classes, orders, genera, and species 

 to each other and to external conditions, and the action and reaction 

 of these in the struggle for life the geographical distribution of spe- 

 cies and their relation to climate and other physical conditions, the 

 whole constituting a complexly adjusted and permanent equilibrium. 

 This is a science of great importance, but one not yet distinctly con- 

 ceived, much less named.* Or, we may study the same in its gradual 

 progressive approach, throughout all geological times, toward the pres- 

 ent condition of things, by continual changes in the parts, and there- 

 fore disturbance of equilibrium and readjustment on a higher plane 

 with more complex inter-relations. This is development of the organic 

 kingdom. In the popular mind it is, par excellence, evolution. 



We might multiply examples without limit. There are the same 

 two points of view on all subjects. As already said, in the one we are 

 concerned with things as they are ; in the other, with the process by 

 which they became so. This " law of becoming " in all things this 

 universal law of progressive inter-connected change may be called 

 the law of continuity. We all recognize the universal relation of 

 things, gravitative or other, in space. This asserts the universal causal 

 relation of things in time. This is the universal law of evolution. 



But it has so happened that in the popular mind the term evolution 

 is mostly confined to the development of the organic kingdom, or the 

 law of continuity as applied to this department of Nature. The reason 

 of this is that this department was the last to acknowledge the suprem- 

 acy of this law ; this is the domain in which the advocates of super- 

 naturalism in the realm of Nature had made their last stand. But it 

 is wholly unphilosophical thus to limit the term. If there be any evo- 

 lution, par excellence, it is evolution of the individual or embryonic 

 development. This is the clearest, the most familiar, and most easily 

 understood, and therefore the type of evolution. We first take our 

 idea of evolution from this form, and then extend it to other forms of 

 continuous change following a similar law. But, since the popular 

 mind limits the term to development of the organic kingdom, and 

 since, moreover, this is now the battle-ground between the advocates 

 of continuity and discontinuity of naturalism and supernaturalism in 

 the realm of Nature what we shall say will have reference chiefly to 

 this department, though we shall illustrate freely by reference to other 

 forms of evolution. 



* The term chorology, used by Haeckel, nearly covers the ground. 



