CHAPTER VIII 

 TRANSFORMISM 



By transformism we mean that some of the individuals of a 

 naturally occurring category of organisms undergo changes in their 

 morphology, such that the definition of the category no longer 

 describes them. In this statement we necessarily (but provision- 

 ally) restrict the conditions of the problem, (i) We must, first 

 of all, consider naturally occurring categories of organisms because 

 we have to apply the conception of transformism to organisms 

 living in the wild and apart from deliberate human control and 

 (2) we must mainly consider the structure, or morphology, of 

 organisms because w^e only know the structures of most of the 

 organisms that lived in the past. It will be necessary, of course, 

 to consider also the results of domestication of plants and animals, 

 and it is also necessary that we consider the changes of organic 

 functioning and behaviour that are, in a way, expressed in changes 

 of morphology. 



84. ON CATEGORIES OF ORGANISMS 

 We can form really clear ideas of the categories, species and 

 local races and it is from these that we start our discussion. 

 Resuming what has been said before (in Section 77^) we note that 

 a species is a group, or category, of organisms such that all the 

 individuals resemble each other more than they resemble the 

 individuals of other categories. Thus well-known species can 

 always be easily recognized. Further, the individual organisms 

 belonging to the same category are immediately and ultimately 

 fertile with each other. Local races are categories within the 

 species such that the individuals belonging to one of them resemble 

 each other more than they resemble the individuals belonging 

 to other local races. The organisms in all the local races of a 

 species are usually immediately fertile with each other, though 

 the ultimate interfertility of the individuals of diflferent local races 



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