CHAPTER VI 



TRANSFORMISM 



The species is therefore a group of organisms all of 

 which exhibit the same morphological characters. 

 This sameness is not absolute, for the individuals 

 composing the species may vary from each other 

 with respect to any one character. But the range of 

 these variations is limited. They fluctuate about an 

 imaginary mean value which remains constant in the 

 case of a species which is not undergoing selection, 

 and is therefore nearly the same throughout a series 

 of generations. The formal characters which we 

 regard as diagnostic of the species are these imaginary 

 mean ones. 



It is possible to breed from stock a very great 

 number of animals, all of which are connected by a tie 

 of blood-relationship, that is, all have descended from 

 the same ancestor or ancestors. Such an assemblage 

 of animals would resemble those assemblages living 

 in the wild which we call species, in that a certain 

 morphological similarity would be exhibited by all the 

 individuals. If the breeding were conducted so as to 

 avoid selection, the range of variability would be very 

 much the same as that observed in the wild race. The 

 two groups of animals — that bred artificially, and that 

 observed in natural conditions — would be very much 

 alike, and it is impossible to resist the conclusion that 

 the natural race, like the artificial one, is a family in 



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