USE AND DISUSE 37 



grow into the possession of full adult size and power in the 

 total absence of all exercise. We know that it cannot do so. 

 In the human being, especially civilized human being, the 

 latest product of evolution, the descendant of thousands of 

 generations during which acquirements were constantly made 

 to a larger extent than by any other animal, we should find 

 the largest number of acquirements crystallized into inborn 

 traits. The exact contrary is the fact. Owing to evolution 

 of man's great power of making acquirements, his inborn 

 traits have actually undergone regression. He attains 

 maturity only by making afresh the same acquirements his 

 near and remote ancestors made. Without them he is 

 incapable of independent existence. 



62. It may be argued that amongst the higher animals 

 use increases, not only the number of acquirements, but the 

 power of making them as well, and that it is the latter 

 acquirement that is transmitted. But this view likewise is 

 plainly erroneous. In the human being, for instance, the 

 power of making acquirements, mental and physical, is 

 greatest in infancy, and it is mainly by virtue of it that the 

 infant develops into adult man. But the power constantly 

 declines during the passage from infancy to old age, till it 

 almost disappears in the old man, who can grow neither 

 physically nor mentally. Here again, since nothing is 

 acquired, nothing can be transmitted. 



63. Moreover, it is to be noted that this power of develop- 

 ing, of growing in response to the stimulation of use and 

 exercise, is not equally distributed to all parts of the body. 

 By labour almost any man may, if he chooses, increase the 

 size of his muscles or the thickness and density of his skin 

 (e. g. on his hands), but, though no parts are more used than 

 the joints, the teeth, and the tongue, no man can by exercise 

 increase their size. The power of growth in response to 

 exercise resides, therefore, not especially in the parts which 

 are most used, but in the parts in which it is most useful in 

 other words, in those parts where it has been evolved, not 

 by use, but by Natural Selection. 



63a. Very clearly the appeal to evolution affords no support 

 to the Larnarckian doctrine of heredity. The Bathmic 

 doctrine we have already rejected. There remains only the 

 Neo-Darvvinian doctrine. It has been declared inadequate 

 by its opponents. Whether or not it accords with, and is 

 capable of explaining, all the facts of evolution, may next be 

 examined. 



