SEGREGATION A FUNDAMENTAL LAW IN THE ORGANIC WORLD. 47 



and partition. The need of such terms will, I am sure, be recognized 

 by many, though some may not consider the words I have chosen the 

 best. 



2. Segregation is a Fundamental Law in the Organic World. 



One sphere in which it operates is racial (or aptitudinal) segrega- 

 tion, produced by the intcrgeneration of individuals with like innate 

 characters. Another sphere is social (or habitudinal) segregation, 

 produced by the association with each other of individuals with like 

 acquired characters. Segregate generation (i. c., the generation of 

 like with like), is a condition on -which the present structure of the organic 

 world depends. Without segregate generation the differences of 

 races, species, genera, and the higher groups could never have arisen, 

 and if it were possible that it should cease, all these distinctions 

 would ere long be obliterated. The fact that race characters are 

 hereditary renders it certain that freely intergenerating races will, in a 

 few generations, become one race. But the fundamental .nature of 

 the organic world is such that the only cases in which the law of segre- 

 gation can be broken down are those in which the divergence is com- 

 paratively small. When amalgamation takes place it is usually 

 varieties of the same species that unite. When physiological incom- 

 patibility has once been fully established, the segregation is never 

 broken down ; but, on the other hand, as long as there is any plasticity 

 in a race, it is possible that new segregations may be introduced and 

 one race divided into two or more races. 



Having observed that segregate generation is the fundamental 

 principle by which the world of sexually reproducing organisms is 

 maintained, and having discovered that the art of breeding, by which 

 the multitude of domestic races has been produced, rests on the 

 control of segregate breeding, we propose to make careful investiga- 

 tion of the different forms of control influencing this principle and of 

 the effects thus produced. 



As an equivalent for segregate generation (or the breeding of like 

 individuals with like), Romanes has proposed the term "homogamy." 

 An objection to its use in this meaning is, however, found in the fact 

 that in botanical language the same term has a somewhat different 

 meaning. 



It should be noted that this statement concerning the breeding of 

 like with like does not imply that creatures freely mating with each 

 other are entirely free from differences. Of multicellular organisms 

 no two were ever found to be exactly alike ; if, therefore, there is any 

 mating of these creatures, it must be the mating of creatures that 

 are not completely the same, either in structure or function. The 



