not always as we find them today, but that the more per- 

 fect had developed from simpler forms through a series 

 of modifications. These thoughts were at first advanced 

 with some hesitation, and were confined to narrow circles. 

 They received, however, maiterial support when, during the 

 fourth decade of the 19th century the splendid discovery 

 was made (by K. E. von Baer) that every organism is slow- 

 ly developed from a germ, and in the process of develop- 

 ment passes through temporary lower stages to a perma- 

 nent higher one. Even at that time many naturalists be- 

 lieved in a corresponding development of the whole series 

 of organisms, without of course being able to form a clear 

 conception of the process. Such was the state of affairs 

 when Darwin in the year 1859 published his principal work, 

 The Origin of Species by Means of Natural Selection. In 

 this work for the first time an exhaustive attempt was 

 made to sketch a clear and completely detailed picture of 

 the process of development. 



Darwin started with the fact that breeders of animals 

 and growers of plants, having at their disposal a large 

 number of varieties, always diverging somewhat from eacli 

 other, choose individuals possessing characteristics which 

 they desired to strengthen, and use only these for procrea- 

 tion. In this manner the desired characteristic is gradually 

 made more prominent, and the breeder appears to have 

 obtained a new species. Similar conditions are supposed 

 to prevail in Nature, only that there is lacking the select- 

 ing hand of the breeder. Here the so-called principle of 

 Natural Selection holds automatic sway by means of the 



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