WHAT IS THE ORIGIN OF SPECIES? 1 93 



peated. This leads us to the further analysis of this process 

 — the plasticity or \.\\c permanency of the characters. 



Plasticity of Characters.— In the characters recognized as 

 plastic in the development of the individual there is possible 

 adjustment to changed conditions. So long then as any char- 

 acter is in a plastic, undeterminate condition, it is evidently 

 not essential. All varietal characters may be regarded as in 

 such a condition. The theory of Darwin explains that these 

 tentative characters will necessarily prove of advantage or of 

 disadvantage; it may be extremely slight, but, in a close con- 

 test, sufficient to give the possessor greater or less chance of 

 success in the struggle for life ; and the perpetuation of such 

 characters will be brought about by the living of the possessor 

 of the favorable variation to perpetuate its kind, and the 

 death of the others. 



Origin of Species from the Physiological Point of View. — At 

 this point we need to consider the origin from the physiologi- 

 cal standpoint. The name for the process of assuming mor- 

 phological and physiological characters by the individual is 

 development, as has already been explained. Reproduction is 

 that process by which one set of individuals initiates the cycle 

 of development for a new individual. The principle deter- 

 mining the repetition of like characters in the parent and off- 

 spring is called Heredity or InJieritance. Variability is the 

 principle expressed in the tendency of all vigorous organisms 

 to exceed the mere repetition of ancestral characters by diver- 

 gences. Darwin's theory of the origin of species was pro- 

 posed to account for the existence of different species by a 

 physiological process. 



Darwin's Theory of the Origin of Species. — The full title of 

 Darwin's work is, " Theory of the Origin of Species by Means 

 of Natural Selection, or the Preservation of Favored Races in 

 the Struggle for Life," and its chief points are the following: 



1. Variability Darwin found to be a natural law in the 

 development of all plants and animals. 



2. Artificial Selection. — Darwin observed that men, by 

 selecting, under domestication, plants or animals which 

 already possess particular varietal characters, can, by breeding 

 them together, and by preventing their mixing with other 



