44 THE PRINCIPLES OF HEREDITY 



particular structures, the race follows the gradual trans- 

 formation in its surroundings. Always there is minute 

 adaptation. If the progressive change (e.g. increased size 

 and vigour), instead of affecting the whole organism, 

 affected only particular organs, the species would not only be 

 thrown out of harmony with its environment, but the different 

 structures of the body would be thrown out of harmony with 

 each other. In either case Natural Selection could not 

 remedy the defect, for if the whole species were acted on 

 there could be no regressive variations by the selection of 

 which the specific mean could be restored. If the whole 

 species were not acted on Natural Selection could only destroy 

 the individuals that were affected. In the former case there 

 would be no adaptive change ; in the latter no specific change 

 whatever. 



74. On the other hand, if the agency were an injurious one, 

 one which caused regressive variations, for example a virulent 

 toxin like that of malaria which circulates for prolonged 

 periods in the blood of almost every individual within certain 

 areas, then the race would helplessly degenerate, for here 

 there would by no progressive variations by means of which 

 Natural Selection could restore the balance. 



75. If we conceive the species as exposed to a number of 

 influences, part of which produced progressive and part re- 

 gressive changes, exactly the same results would follow. The 

 species would still drift helplessly in the direction of the sum 

 of these changes. Once again Natural Selection could not 

 possibly act. Again there could be no adaptation to the 

 environment. 



76. Very dearly, then, the doctrine that variations are 

 commonly caused l)y the action of the environment on the germ- 

 plasm is incompatible with the doctrine of Natural Selection. 

 Indeed it is incompatible with every conceivable theory of evolu- 

 tion. Adaptation to the environment by Natural Selection can 

 proceed only when the environment has little or no part in the 

 causation of variations, when variations are wholly or almost 

 wholly spontaneous. The Lamarckian doctrine is nothing 

 more than a special application of the doctrine that variations 

 are caused by the action of the environment. In multicellular 

 organisms the immediate environment of the germ-plasm is 

 the soma. Lamarck imagined that adaptive changes in the 

 soma so affects the germ-plasm that they are reproduced as 

 variations in the offspring. He forgot that all changes in the 

 soma are not adaptive, and that adaptive changes would be 

 of little avail if the rest were non-adaptive. Nevertheless 



