188 
THE DESCENT OF MAN. 
Part I. 
mals as are these two latter groups conjoined. This 
yiew has not been accepted, as far as I am aware, by 
any naturalist capable of forming an independent judg- 
ment, and therefore need not here be further con- 
sidered. 
We can understand why a classification founded on 
any single character or organ — even an organ so won- 
derfully complex and important as the brain— or on the 
high development of the mental faculties, is almost sure 
to prove unsatisfactory. This principle has indeed been 
tried with hymen opterous insects; but when thus classed 
by their habits or instincts, the arrangement proved 
thoroughly artificial . 3 Classifications may, of course, be 
based on any character whatever, as on size, colour, or 
the element inhabited ; but naturalists have long felt a 
profound conviction that there is a natural system. This 
system, it is now generally admitted, must be, as far 
as possible, genealogical in arrangement, — that is, the 
co-descendants of the same form must be kept together 
in one group, separate from the co-descendants of any 
other form ; but if the parent-forms are related, so will 
be their descendants, and the two groups together will 
form a larger group. The amount of difference between 
the several groups — that is the amount of modification 
which each has undergone — will be expressed by such 
terms as genera, families, orders, and classes. As we 
have no record of the lines of descent, these lines can 
be discovered only by observing the degrees of re- 
semblance between the beings which are to be classed. 
For this object numerous points of resemblance are of 
much more importance than the amount of similarity 
or ; dissimilarity in a few points. If two languages 
were found to resemble each other in a multitude of 
Westwood, ‘ Modern Class, of Insects/ vol. ii. 1840, p. 87. 
