THE STRUGGLE FOE EXISTENCE 35 



tiou upon itself of the activity of the animal or plant. 9 

 The occupation of a blacksmith is one which develops 

 the muscles of the arm by the continuous and vigorous 

 form of exercise of hammering iron. If the blacksmith 

 has a son who becomes a bookkeeper, does the son have 

 any stronger right arm than he would have had if his 

 father had been an office clerk? Certainly the size of 

 a muscle is increased by use, and .decreased size results 

 from disuse. Are these effects inherited by the off- 

 spring? One point must be noted carefully: the 

 fact that the blacksmith does develop strong muscles as 

 a result of the exercise shows that he must have an in- 

 born capacity for developing strong muscles by exer- 

 cise. But if the blacksmith inherited from his parents 

 the ability to develop strong muscles by exercise, his 

 son in turn would inherit from him the same ability. 

 Exercise or the lack of it would therefore only bring 'out 

 the latent tendency or simply leave the natural tendency 

 to work itself out. The innate capacity would be in- 

 herited, not the accentuated development induced by ex- 

 ercise. The child is not the child of the biceps muscle 

 of the parent, but the child of the germ cells of the 

 parent. The biceps muscle of the parent has little to do 

 with these germ cells. How therefore, could the use of 

 biceps muscle in the arm of the parent so affect the off- 

 spring that he would have stronger biceps than if his 

 parent had not developed his own through exercise? 

 There is little evidence to support the doctrine of trans- 

 mission of acquired characteristics. 



But if there is no direct transmission of the individual 

 modifications produced by environment, wherein does 

 the importance of function and environment consist? 



d., p. 75, 



