108 Dynamic Theory. 



abound in every animal and which have become f unctionless by disuse. 

 Every one can recall examples of modifications of the functional power 

 of organs by disuse or by greater use of them. Skill in the performance 

 of any action depends upon practice or use. The. eye of the Dakota 

 Indian hunter is quicker to discern distant objects than is that of an or- 

 dinary watchmaker or tailor. The ear of a musician will detect an in- 

 harmony quicker than that of the Dakota. The hand of the blacksmith 

 is not generally well adapted for fingering a piano, nor that of the parlor 

 belle for shoeing a horse. Now it is always admitted that such differ- 

 ences in functional value are brought about by habit and use ; but it is 

 assumed that the organs are essentially the same. This assumption is 

 incorrect. A full appreciation of the structural differences caused by 

 habit goes a long way toward an understanding of evolution. The fact 

 is that every movement of an organism implies waste of tissue, the re- 

 pair of which depends on the environment. This process of the waste 

 and repair of infinitessimal parts is incessant throughout life. The new 

 parts that are incorporated in the system are in every case in some de- 

 gree different from the old parts that the} T replace. Habit or use deter- 

 mines the parts in which the greater amount of waste and repair shall 

 take place. No animal is precisely the same for two days in succession 

 and it is chiefly the nature of his activity, in short his habit, that deter- 

 mines his modification. This point will be insisted upon further on. 



Habit is determined in its turn directly by the necessities of the en- 

 vironment the climate, soil, vicissitudes of heat and cold, dry ness and 

 moisture, light and darkness, and indirectly by these same necessities in 

 their influence on the food supply as to quality and quantity, and yet 

 more indirectly by their influence in the production of competitive 

 races of animal and vegetable organisms. And when we come to speak 

 of competition we must see at once not only that such competition nec- 

 essarily exists between different races, but also between individuals of 

 the same race. Most animals and all vegetables produce a large num- 

 ber of germs and seeds. If it were possible for all these to live and 

 continue to reproduce without check, the world would long since have 

 become too small to hold them. 



The human race under favorable conditions will double in numbers 

 every twenty years. Let the present population of the earth be esti- 

 mated at 1,200,000,000, the total amount of land on earth at 52,000,- 

 000 square miles, and the increase of population to be a doubling once 

 in fifty years. On these conditions in one thousand } r ears, or in A. D. 

 2892, there will be people enough to cover the entire land area and al- 

 low each one a space of only twelve by fourteen inches to stand and 

 make their living on. If they could be conceived to stand thus and live 

 on air and continue to increase, the succeeding generations arranged 



