Sentence:  That he mastered every aspect of his medium according to his own great talents and contemporary judgments , is a good and solid symbol of his people under the tremendous pressures of proclaiming and practising the rigors of a new culture ; and perhaps of even greater significance - his music is strong 20 th Century evidence of the <WSD>effectiveness</WSD> of Evolution , based on a broad Traditionalism for the creative art of music . 
Meaning of the word marked with <WSD> tags:  power to be effective; the quality of being able to bring about an effect