80 THE THEORY OF EVOLUTION 



diately negatived by the contrast between the blood 

 of mammals and that of birds. It could hardly be 

 maintained that an ostrich and a parrot are more 

 nearly allied than a wolf and a hyena and yet that 

 would be the inference from the blood tests. Like 

 all other anatomical and physiological characters, 

 the chemical composition of the blood is subject to 

 change in the course of evolution and these develop- 

 mental changes do not keep equal pace in all parts 

 of the organism. It is the rule rather than the ex- 

 ception to find that one part of the structure ad- 

 vances much more rapidly than other parts, such as 

 the teeth, the skull, or the feet. The human body 

 is, fortunately for us, of rather a primitive kind, 

 while the development of the brain is far superior 

 to that of any other mammal and this great brain- 

 development has necessitated a remodeling of the 

 skull. On the other hand, the skeleton, limbs, 

 hands and feet are but slightly specialized. In 

 the elephant tribe, so far as we can trace them 

 back in time, there has been little change, save in 

 size, in the structure of the body or limbs, while the 

 teeth and skull have passed through a series of re- 

 markable changes. It is for this reason that it is 

 unsafe to found a scheme of classification, which is 

 meant to be a brief expression of relationship, upon 

 a single character, for the result is almost invariably 

 misleading. The results of blood tests must be 

 critically examined and checked by a comparison 

 with the results obtained by other methods of inves- 



