EVOLUTION CAUSED BY CHANGEFULNESS 163 







Evolution may, then, be defined as the develop- 

 ment rather of impulses than of organs. Some of 

 these affect the body, others the character, and 

 in tracing the affinities of plants and animals, 

 and of races of mankind, we are as likely to find 

 clues in behaviour as in bodily features. The 

 evolution of species in the world of life has been 

 commonly attributed to natural or sexual selec- 

 tion. But this confuses a condition with a cause. 

 Evolution must proceed from a changefulness 

 that is inherent in living creatures, for, unless 

 changes occurred, there would, indeed, be nothing 

 for selection to act upon. It would be pleasing 

 to feel that this changefulness was systematically 

 directed towards the organism's benefit. But 

 against such a supposition there is an overwhelm- 

 ing mass of evidence. Variations occur in every 

 direction. Those that are harmful are eliminated 

 by the struggle for life : those that are beneficial, 

 or harmless, may survive. But we need not 

 assume, on the evidence that has been collected, 

 that variation is entirely uncontrolled that in 

 no case is it directed by outside influences. Facts 

 are very numerous which appear to indicate that 

 plants and animals may be stimulated to vary 

 their forms or dispositions by their environment, 

 by their habits, or by the imitative impulse ; 

 and in this case the variations would be generally 

 to their advantage. We cannot absolutely deny 

 that the giraffe may have been stimulated to vary, 

 so as to lengthen its neck, by continued striving 

 after higher foliage ; that the migration of swal- 

 lows is not impelled by an instinct which was 

 generated by habit, or that Arctic animals did 

 not gradually acquire the faculty of turning 

 white during winter by subconscious imitation of 

 the colour of snow, 



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