It is therefore a matter of the first importance to consider how character is produced or modified. Possibly to some it may appear presumptuous to apply to the mind those natural laws which it is now generally agreed apply to bodily development. Yet even the probabilities of chance distribution may be shown to apply to the varieties of mind; both by rough observation in general, and also by a test case quantitatively applied (see _Religion and Conscience in Ancient Egypt_). A feeling against this treatment of the mind by material law is based on the idea that it implies an absence of free-will. But, to take an illustration, a railway company may be certain of carrying very closely the same number of passengers each day, without in the least embarrassing the free-will of any passenger as to whether or no he will travel. Let us notice, therefore, how the various principles of physical modification are applicable also to mental change. Whether it may be that changes take place by the inheritance of acquired characteristics, or whether they occur solely by accidental variation which proves beneficial, is a much debated question which is not requisite for us to settle here. It is agreed that in the physical life of all animals it may be seen that: (1) Favourable variations give a determining advantage to one individual over another, or to one more than another against a common enemy; (2) Useful variations tend to be maintained in successive generations; (3) Artificial conditions tend to produce variation; (4) Greater variability accompanies unusual developments; (5) Growth is directed and encouraged by use; and (6), as the total activity is limited, therefore disuse causes atrophy and degradation, by favouring of parts more used. To these follows the important corollary (7): Variation being only of benefit where there is competition in which it gives an advantage, its improvements will cease to be maintained in the absence of competition; it is only competition which makes improved variations permanent. For instance, if there were no carnivora the swifter deer would not have found their pace a benefit, and there would be no sufficient cause for their attaining their present swiftness. In place of looking on selection as merely a struggle we must look on it as the sole physical means of permanent elevation, the motor which has raised every species to its present point of ability.