The process of absorption of smaller groups and their unification into larger ones, when carried out completely in any land, tends to arrest all further growth, not simply because there is no further room for expansion by the absorption of other divergent tribes, but also because the "cake of custom" is apt to become so hard, the uniformity enforced on all the individuals is liable to become so binding, that fruitful variation from within is effectually cut off. The evolution of relatively isolated or segregated groups necessarily produces variety; and the process whereby these divergent types of life and thought and organization are gradually brought together into one large community provides wide elements of variation, in the selection and general adoption of which the evolution of the whole community may be secured. But let the divergent elements of the lesser groups once be entirely absorbed by the composite community and let the "cake of custom" become so rigid that every individual who varies from it is branded as a heretic and a traitor, and the progressive evolution of that community must cease. The great problem, therefore, which then confronts man and seems to threaten all further progress is, how to break the bondage of custom so as to secure local or individual variations. This can be done only through some form of individualism. The individual must be free to think and act as experience or fancy may suggest, without fear of being branded as a traitor, or at least he must have the courage to do so in spite of such fears. And to produce an effect on the community he must also be more or less protected in his idiosyncrasies by popular toleration.