AFFINITIES AND GENEALOGY. 169 



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 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 multi- 

 tude 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 adapta- 

 tions 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 use- 

 less and rudimentary organs, or not now functionally active, 

 or in an embryological condition, are by far the most serv- 

 iceable for classification ; for they can hardly be due to 

 adaptations within a late period; and thus they reveal the 

 old lines of descent or of true affinity. 



We can further see why a great amount of modification 

 in some one character ought not to lead us to separate 

 widely any two organisms. A part which already differs 

 much from the same part in other allied forms has already, 

 according to the theory of evolution, varied much; conse- 

 quently it would (as long as the organism remained exposed 

 to the same exciting conditions) be liable to further varia- 

 tions of the same kind; and these, if beneficial, would be 

 preserved, and thus be continually augmented. In many 

 cases the continued development of a part, for instance, of 

 the beak of a bird, or of the teeth of a mammal, would not 

 aid the species in gaining its food, or for any other object; 

 but with man we can see no definite limit to the continued 

 development of the brain and mental faculties, as far as 

 advantage is concerned. Therefore in determining the 

 position of man in the natural or genealogical system the 

 extreme development of his brain ought not to out- 

 weigh a multitude of resemblances in other less important 

 or quite unimportant points. 



The greater number of naturalists who have taken into 



