50 THE HISTORY OF CREATION. 
all organic individuals which were very similar, or almost 
identical in form, and which could only be distinguished 
from one another by very unimportant differences. On the 
other hand, they considered as different species those 
individuals which presented more essential or more striking 
differences in the formation of their bodies. But of course 
this opened the flood-gates to the most arbitrary proceedings 
in the systematic distinctions of species. For as all the 
individuals of one species are never completely alike in 
all their parts, but as every species varies more or less, no 
one could point out which degree of variation constituted 
a really “good species,’ or which degree indicated a “mere 
variety.” 
This dogmatic conception of the idea of species, and 
the arbitrary proceedings connected with it, necessarily 
led to the most perplexing contradictions, and to the most 
untenable suppositions. This is clearly demonstrable in 
the case of the celebrated Cuvier (born in 1769), who 
next to Linneeus has exercised the greatest influence on 
the study of zoology. In his conception and definition of 
the idea of species, he agreed on the whole with Linnzeus, 
and shared also his belief in an independent creation of 
individual species. Cuvier considered their immutability 
of such importance that he was led to the foolish asser- 
tion—“ The immutability of species is a necessary con- 
dition of the existence of scientific natural history.” As 
Linnzeus’ definition of species did not satisfy him, he 
made an attempt to give a more exact and, for syste- 
matic practice, a more useful definition, in the following 
words: “ All those individual animals and plants belong to 
one species which can be proved to be either descended 
