148 The Descent of Man. Part 1. 



doubt the difference is bridged over by other insects ; and this 

 is not the case with man and the higher apes. But we have 

 every reason to believe that the breaks in the series are simply 

 the results of many forms having become extinct. 



Professor Owen, relying chiefly on the structure of the brain, 

 has divided the mammalian series into four sub-classes. One of 

 these he devotes to man; in another he places both the 

 Marsupials and the Monotremata; so that he makes man as 

 distinct fiom all other mammals as are these two latter groups 

 conjoined. This view has not been accepted, as far as I am 

 aware, by any naturalist capable of forming an independent 

 judgment, and therefore need not here be further considered. 



We can understand why a classification founded on any single 

 character or organ — even an organ so wonderfully 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 hymenopterous insects; 

 but when thus classed by their habits or instincts, the arrange- 

 ment proved thoroughly artificial.^ 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, apart from the 

 co-descendants of any other form ; but if the parent-forms are 

 related, so will be their descendants, and the two groups to- 

 gether will form a larger group. The amount of diiference 

 between the several groups— that is the amount of modification 

 which each has undergone — is expressed by such terms as 

 genera, families, orders, and classes. As we have no record of 

 the lines of descent, the pedigree can be discovered only by 

 observing the degrees of resemblance between the beings which 

 are to be classed. For this object numerous points of resem- 

 bl.ince 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 words and 

 points of construction, they would be universally recognised as 

 having sprung from a common source, notwithstanding that 

 they differed greatly in some few words or points of construction. 

 But with organic beings the points of resemblance must not 

 consist of adaptations to similar habits of Ufe : two animals may, 

 for instance, have had their whole frames modified for living in 



Weslwixid, ' Modern Class of Jnsects,' toV ii. 1840, p. 87. 



