THEORIES OF EVOLUTION 55 



times, held that natural selection played the greatest part 

 in the development of new characters. The speed of the 

 deer will serve again in order to explain the working of 

 natural selection. In this case the explanation is, that those 

 deer which possessed the greatest inborn capacity for de- 

 veloping speed were those that escaped from the animals 

 that hunted them. Thus deer possessing this inborn char- 

 acter would survive and produce offspring in greater numbers 

 than those that lacked it. The offspring would vary from 

 the parents and from each other, some towards a greater 

 capacity for developing the speed, some remaining about 

 the same and varying perhaps in other characters, and 

 others again would vary towards less speed. With the 

 offspring the same thing would happen again ; those with 

 the greatest speed would have the best chance of escaping 

 from their enemies, and would thus survive and produce 

 offspring. At every generation, in fact, those individuals 

 which varied toward less speed would be eliminated ; while 

 those which varied toward greater speed would possess even 

 greater advantages than their parents. As long, therefore, 

 as the selection was kept up, that is, as long as other animals 

 continued to hunt the deer, the deer would go on developing 

 greater speed until they reached a point where the race 

 had attained a considerable amount of safety by this means. 

 And even then, the high standard of speed would be main- 

 tained by the elimination of individuals which varied toward 

 less speed, as long as beasts of prey continued to hunt the 

 deer. 



The theory that evolution is due to natural selection 

 acting upon inborn characters, and upon inborn characters 

 only, is due to Weismann. Weismann formulated his idea 

 in his theory of the continuity of the germ-plasm. His 

 theory is that the hereditary substance (the germ-plasm) 

 always remains distinct in the body of the multicellular or- 

 ganism. When the single cell the fertilised ovum divides 

 into two, one of these daughter cells is destined to produce 

 the reproductive cells (the sperms or ova), the other is' 



