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 W orld. 
One sphere in which it operates is racial (or aptitudinal) segrega- 
tion, produced by the intergeneration 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 (1. e., the generation of 
like with like), 7s 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 
