14 THE PRINCIPLES OF HEREDITY 



from existence of specific or racial change, but from the fact 

 that this change (i. e. evolution) has led, since the beginning 

 of life, to the close adaptation of every race of animals and 

 plants to its own successive environments. Either the 

 environment has acted on species, which have reacted to it, 

 or their adaptive changes were miraculous. There is no third 

 alternative. If the environment caused the adaptation, it 

 must have done so by means of natural selection, 1 or by 

 causing individuals to make adaptive acquirements which 

 were transmitted to offspring. Again there is no real 

 alternative. It is significant that when structures and 

 organs, for example the limbs of snakes, lose their utility 

 that is when they are no longer used nor selected they 

 undergo degeneration, not growth. 



24. The Bathmic theory of heredity and evolution may, 

 then, be ruled out of court. We are left with the 

 Lamarckian and Neo-Darwinian doctrines. One, or the 

 other, or both combined must furnish the true explanation 

 of evolution. 



25. If we believe with Lamarck that acquirements are 

 transmissible, we find ourselves committed at once to a 

 theory of evolution. In the face of common experience, we 

 need not believe that acquirements tend to be transmitted in 

 their entirety, that a dog which has lost its tail tends to 

 have tailless puppies, or that a man who has made great 

 mental acquirements tends to have children endowed at 

 birth with all that he achieved with pain and toil. But we 

 are committed to the doctrine that the dog's loss and the 

 man's gain will be inherited to some extent, however slight, 

 and that, if many successive generations of dogs and men 

 make similar acquirements, the race of dogs will ultimately 

 become tailless and that of men highly endowed mentally. 

 In brief, the Lamarckian doctrine supposes that the effects 

 of everything that benefits or injures the individual, including 

 the effects of all use and disuse, are to some extent trans- 

 mitted to offspring, and that evolution or degeneration 

 results from the accumulation during generations of these 

 transmitted effects. It supposes, for example, that certain 

 antelopes run swiftly because ancestral antelopes, in their 

 efforts to escape enemies, developed the structures which 

 subserve speed. It supposes that stags have antlers, because 

 originally their hornless ancestors developed the habit of 



1 "Germinal Selection" and other similar hypotheses may be 

 considered as coming under the category of Natural Selection. See 

 158-9. 



