Our abstract thought, which we use even in the pursuit of popular science, which we regard today as quite natural — this thinking activity was by no means always so natural and simple. In order to illustrate what I say, let me give you a radical example. You will think it strange that while for all of you it is quite natural to speak of a “fish,” it was by no means natural for primitive peoples to do so. Primitive peoples are acquainted with trout and salmon, cod and herring, but “fish” they do not know. They have no such word as “fish,” because their thought does not extend to such abstract generalization. They know individual trees, but “tree” they do not know. Thinking in such general concepts is by no means natural to primitive races even in the present time. This mode of thinking has indeed only entered humanity in the course of its evolution.
Source: Rudolf Steiner – GA 146 – The Occult Significance of the Bhagavad Gita: Lecture 2 – Helsinfors, 29th May 1913