CHAPTER III
Of all young creatures, the human infant is the most helpless, the least equipped with instinct for the battle of life; of all grown creatures the adult man is the most helpful, the best equipped with reason for the strife. Beyond all other creatures, the human being possesses the power of mentally varying in response to stimulation from the environment, and thereby bringing himself into completer harmony with it. And always, owing to the imitative instinct, as strong in him as in lower animals, his variations tend to reproduce those of his immediate predecessors. At birth his mind, mainly the product of that great mass of nerve tissue, the cerebrum, is an unploughed field, which, ploughed by experience, brings forth, according to the seed that is sown; a blank unwritten page on which chance shall write; a mass of clay ductile to the hands of the moulder.
If we bear steadily in view the two cardinal facts, (1) that the mind of man is compounded almost entirely of acquired traits,—acquired knowledge, acquired ways of thinking and acting, acquired likes and dislikes, &c.; and (2) that the action of Natural Selection has plainly been such as to cause in him, not an evolution of this or that mental trait, but mainly of a power of acquiring mental traits in response to stimulation, we are able to understand many things which at first sight seem puzzling.
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