THE DESCENT OR OBIOIN OF- MAN 199 



unsatisfactory. This principle has indeed been tried with 

 hymenopterous insects; but when thus classed by their 

 habits or instincts, the arrangement proved thoroughly arti- 

 ficial.' Classifications may, of course, be based on any char- 

 acter 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 arrange- 

 ment — 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 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 recorcf of the 

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

 serving the degrees of resemblance between the beings which 

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

 semblance 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 recog- 

 nized as having sprung from a common source, notwithstand- 

 ing that they differed greatly in some few words or points of 

 construction. But with organic beings the points of resem- 

 blance must not consist of adaptations to similar habits of 

 life: two animals may, for instance, 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 resemblances in 

 several unimportant structures, in useless and rudimentary 

 organs, or not now functionally active, or in an embryologi- 

 cal condition, are by far the most serviceable for classifica- 

 tion; for they can hardly be due to adaptations within a 



* Westwood, "Modern Class of Insects," vol. ii., 1840, p. SI. 



