Convergence of Evidence 119 



the more impressed we are with the fundamental identities 

 in detail and with the probability of kinship roughly pro- 

 portional to degrees of resemblance. 



However much we may wonder at the multiplicity of 

 living forms, we accept it as after all entirely reasonable, in 

 view of the great variety of conditions to which life has had 

 to adapt itself — or to which living beings have had to be 

 adapted. The marvelous adaptations presented by each 

 species of plant and animal that we take the trouble to ex- 

 amine in detail are accompanied by marvelous adaptations 

 in detail on the part of every organ and process. The same 

 functions are carried on by different plants and animals by 

 means of a great variety of special structures. At the same 

 time we find that all living things are built upon a com- 

 paratively small number of general plans or patterns. This 

 brings about the seeming anomaly that many organs which 

 serve similar functions in many different kinds of organ- 

 isms are fundamentally unlike in their development and 

 structure, whereas numerous structures of identical origin 

 and pattern serve a great variety of functions. We have 

 homologous organs that are not analogous, and analogous 

 organs that are not homologous. Moreover, in a group of 

 organisms that present the same general plan of structure 

 some species show certain organs in a functional state, 

 whereas in other species they are quite without function, 

 and may even be a source of serious harm; and in still other 

 species such unused organs appear to be reduced to mere 

 rudiments or vestiges. 



The unity of life indicated by the identity of funda- 

 mental functions is accompanied by a unity in plan of struc- 

 ture extending to many details that are not in themselves 

 significant as adaptations. There is thus raised a serious 

 doubt as to the specific purposefulness in the origin or cre- 

 ation of a given species, or of all species of plants and ani- 

 mals. And there is thus added a strong appearance of proba- 

 bility to the assumption of the common origin of large 

 groups, with modification in the course of descent. 



