CHAPTER II. 



BIONOMIC LAWS. 

 I. BiONOMic Laws and the Method op their Investigation. 

 1. Bionomics and Its Scope. 



The organic world as we find it consists of many groups of individ- 

 uals, each group, with but few exceptions, being propagated by the 

 union of male and female elements produced by parents belonging to 

 the same group;* while the elements of different groups are either 

 incapable of fruitful union or in nature seldom have an opportunity 

 for such union. Each group possesses characters of its own, distin- 

 guishing it from all other groups ; and these characters are inherited 

 by each successive generation of the group, except in cases known as 

 alternating generations, in which the persistence of character is re- 

 vealed in a series of two or more generations that return to the 

 original form. These persistent groups which are prevented from 

 crossing by the incompatibility of their sexual elements or by some 

 other form of segregation are usually called species; but when the 

 difference of character is slight they are often called varieties; and 

 when the differences are not easily recognized they are not even 

 regarded as different varieties. Each persistent group differing more 

 or less from every other group, and reproducing its own form without 

 commingling with other forms, I call a type. 



The doctrine of evolution teaches that the vast multitude of organic 

 types now inhabiting the world are the descendants of but few and 

 perhaps of but one original type. Bionomics is the science that treats 

 of the origin of organic types and of the relations in which they stand 

 to each other and to the physical environment, f In this volume some 

 of the fundamental laws of bionomics will be considered. 



2. Why we Commence with the Method of Evolution without first proving 

 the Fact of Evolution. 



It may be thought by some of my readers that before discussing the 

 laws of evolution logical method would demand that I should consider 



* -Examples of these exceptions are found in plants that propagate by shoots or 

 bulbs without ever producing seed, such as banana; also in parthenogenetic 

 plants and animals. 



t Prof. E. Ray Lankester has proposed this use of the word "bionomics" in the 

 article on Zoology, in Encyc. Brit., 9th ed. 



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