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392 activities working together. Instead of being isolated from them, as an organ of knowing from organs of motor response, it is the organ by which they interact responsively with one another. The brain is essentially an organ for effecting the reciprocal adjustment to each other of the stimuli received from the environment and responses directed upon it. Note that the adjusting is reciprocal; the brain not only enables organic activity to be brought to bear upon any object of the environment in response to a sensory stimulation, but this response also determines what the next stimulus will be. See what happens, for example, when a carpenter is at work upon a board, or an etcher upon his plate—or in any case of a consecutive activity. While each motor response is adjusted to the state of affairs indicated through the sense organs, that motor response shapes the next sensory stimulus. Generalizing this illustration, the brain is the machinery for a constant reorganizing of activity so as to maintain its continuity; that is to say, to make such modifications in future action as are required because of what has already been done. The continuity of the work of the carpenter distinguishes it from a routine repetition of identically the same motion, and from a random activity where there is nothing cumulative. What makes it continuous, consecutive, or concentrated is that each earlier act prepares the way for later acts, while these take account of or reckon with the results already attained—the basis of all responsibility. No one who has realized the full force of the facts of the connection of knowing with the nervous system and of the nervous system with the readjusting of activity continuously to meet new conditions, will doubt that knowing has to do with reorganizing activity, instead of being something isolated from all activity, complete on its own account.

(ii) The development of biology clinches this lesson, with its discovery of evolution. For the philosophic significance of the doctrine of evolution lies precisely in its emphasis upon