28 Darwin, and after Darwin. 



indicating natural affinities, the less is its value to the 

 creatures presenting it. 



Enough has now been said to show three things. 

 First, that long before the theory of descent was enter- 

 tained by naturalists, naturalists perceived the fact of 

 natural affinities, and did their best to construct a 

 natural system of classification for the purpose of ex- 

 pressing such affinities. Second, that naturalists had 

 a kind of instinctive belief in some one principle run- 

 ning through the whole organic world, which thus 

 served to bind together organisms in groups subor- 

 dinate to groups that is, into species, genera, orders, 

 families, classes, sub-kingdoms, and kingdoms. Third, 

 that they were not able to give any very intelligible 

 reason for this faith that was in them ; sometimes 

 supposing the principle in question to be that of a 

 supernatural plan of organization, sometimes regarding 

 it as dependent on conditions of physiology, and some- 

 times not attempting to account for it at all. 



Of course it is obvious that the theory of descent 

 furnishes the explanation which is required. For it is 

 now evident to evolutionists, that although these older 

 naturalists did not know what they were doing when 

 they were tracing these lines of natural affinity, and 

 thus helping to construct a natural classification I say 

 it is now evident to evolutionists that these naturalists 

 were simply tracing the lines of genetic relationship. 

 The great principle pervading organic nature, which 

 was seen so mysteriously to bind the whole creation 

 together as in a nexus of organic affinity, is now easily 

 understood as nothing more or less than the prin- 

 ciple of Heredity. Let us, therefore, look a little 

 more closely at the character of this network, in 



