190 THE THEORIES OF EVOLUTION 



the burning question in transformism, and for very 

 good reasons. If the modifications undergone by the 

 organism under the influence of its mode of life are 

 transmitted to the offspring, the evolution of species 

 is easily explained without the help of elaborate sys- 

 tems, of auxiliary hypotheses or of logical subter- 

 fuges. 



This is the first explanation suggested by all the 

 facts known about the influence of the use or disuse 

 of organs and about the action of the environment 

 on the structure of individuals. We observe every 

 day that the parts of the body which are particularly 

 active become more developed and that, on the other 

 hand, the organs which are seldom used become 

 atrophied. The strong muscles of a blacksmith's arm, 

 the "horny hands" of a workingman, the small hands 

 of individuals whose ancestors never did any manual 

 labour, the development of certain faculties by con- 

 stant use, the stamp which certain professions put 

 upon a man's physical appearance, are familiar to 

 everybody, and though there is no absolute evidence 

 that such characteristics can be transmitted heredita- 

 rily, there has existed in all times a universal belief in 

 their heritability. In the animal kingdom, the long 

 legs of wading birds, the neck of the giraffe, the 

 degeneration caused by disuse in cases of parasitism, 

 the blindness of animals living in darkness, the atrophy 

 of the whale's forelimbs, are so many examples prov- 



