Successive increments of difference in degree may gradually merge and become exalted into a difference in kind. A number of pendulums might, if unresisted, vibrate in an arc forever, but, if on one of them the movements of the others are suitably concentrated, its arc will gradually increase in amplitude until it becomes a circle.
This principle of concentration appears in organic Nature in the physiological division of labor, and in the adaptation of every organism to some particular environment which may be to it its field and kingdom. Analogy would lead us to suppose that the different duties of the brain are performed by special parts. So directly profitable has the division of labor been found in manufacturing industry, that in many cases it has been pushed to an injurious extreme, for a man is stunted in development when all his powers of mind and body but one remain unexercised. Specialists in art and science discover that their highest excellence can only come with a comprehension of wide principles and study in many various fields.
So far from concentration being invariably useful, diffusion may be a process incident to progress. A lump is soonest leavened by leaven distributed throughout it, crystallization proceeds more swiftly from separate nuclei than from a concrete mass. Analogously, the best, wisest, and most talented men of a people exert a larger influence when scattered through it than if gathered into an over-centralized capital, where they radiate chiefly on each other.
In the laws which have been considered thus briefly, it has appeared that their tendencies are continually progressive; that, while the capital of evolution is being increased, so also is the rate of compound interest by which it accumulates. It is now fitting that some of the causes should be noticed which reduce these tendencies from their theoretical power to the moderate activity we find them really presenting.
A minor and unfavorable sort of natural selection is that made by animals not carnivorous when they have a choice of food; they take the best to be had, and leave the rest to propagate its kind. This residue may be very bad indeed, when the total supply is scanty; in crowded pastures the grazing herds only permit the worst parts of the clover to come to seed, and squirrels always first eat the best nuts stored in their hiding-places, and any surplus that might germinate and grow is commonly of a very poor kind. The acquisition of new powers by an animal is usually accompanied by a gradual and injurious loss of its original ones; neither the omnivorous hog nor the higher primates can number readiness in swimming among their resources, although their inferior ancestry doubtless could. The introduction of machinery is steadily causing us to lose the deftness and dexterity of the old, unaided handicrafts, yet never so much as now were knack and skill of value, for they are indispensable to the designer and inventor in their work. A highly-cultivated citizen of New York, when he pene-
