For it points to the importance of the part which the principle of individuality plays in the great drama daily enacting before our eyes, and which we know as evolution.

It shows, as I shall hope to prove, that individuality bears the same relation to the development of mind that the differentiation of species does to the evolution of organic life: that the degree of individualization of a people is the self-recorded measure of its place in the great march of mind.
All life, whether organic or inorganic, consists, as we know, in a change from a state of simple homogeneity to one of complex heterogeneity.

The process is apparently the same in a nebula or a brachiopod, although much more intricate in the latter.

The immediate force which works this change, the life principle of things, is, in the case of organic beings, a subtle something which we call spontaneous variation.

What this mysterious impulse may be is beyond our present powers of recognition.