LIMITS OF NATURAL SELECTION. 3 



there was a causal relation between environment 

 and useful variations. That this causal relation 

 existed to a limited degree has been generally recog- 

 nised in the accepted theory of the growth or 

 degeneration of organs through use or disuse, the 

 effects of which were supposed to be inherited. 

 Also, the acquired habits of animals were supposed 

 to become the instincts of their later posterity. 

 The reaction of an animal to the influences of its 

 environment was thus supposed to produce- certain 

 changes in the animal, — changes which were called 

 acquired characters, as distinguished from hereditary 

 characters, — and these acquired characters were 

 supposed to be inherited by the posterity of the 

 animal, and thus become hereditary characters. 

 This theory suggests the only clue to a relation 

 between environment and useful variations and 

 development. The biologists who have adhered to 

 these views have been dubbed the " Neo-Lamarck- 

 ian School," while differing from them are others 

 bearing the name of " Neo-Darwinian School." 



In these two schools we have represented the 

 tendencies of the two conceptions of evolution which 

 have existed since Darwin's time. The Neo-Dar- 

 winists have held that natural selection — the 

 potency of which was universally recognised — was 

 alone sufficient to account for all the phenomena 



