144 THE DESCENT OF MAN. 



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

 every reason to believe that Ihe 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 Marsu- 

 pials and the Monotremata; so that he makes man as distinct 

 from 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 judgmentj 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 arrangement proved thor- 

 oughly artificial." Classifications may, of course, be based on any 

 character whatever, as on size, color, 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; b.ut 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 — 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- 

 blance are of much more importance than the amount of sim- 

 ilarity 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 recognized 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 life: two animals may, for in- 

 stance, have had their whole frames modified for living in the 

 water, and yet they will not be brought any nearer to each other 

 in the natural system. Hence we can see how it is that resem- 

 blances in several unimportant structures, in useless and rudi- 

 mentary organs, or not now functionally active, or in an embry- 



" WestwooU, 'Modern Class of Insects,' vol. ii. 1840, p. 87. 



