EVOLUTION AS SHOWN BY THE DEVELOPMENT 

 OF THE INDIVIDUAL ORGANISM 



By Ernest William MacBride 



Professor of Zoology, Imperial College of Science and Technology, 

 London; Vice President of the Zoological Society of London 



According to the theory of evolution as it is applied to 

 20ology the fundamental likenesses or homologies among 

 animals are the expressions of blood relationship. We 

 believe, for example, that all the various species which belong 

 to the cat tribe — such as the domestic cat, the leopard, the 

 jaguar, the puma, the lynx, the lion, and the tiger — are the 

 descendants of a primeval species of cat, just as the dog, 

 the fox, the jackal, and the wolf are the descendants of a 

 primeval species of dog. Furthermore, we believe that the 

 primeval dog and the primeval cat were distant cousins, and 

 that millions of years ago both were represented by one 

 species of primitive carnivore, from which both have been 

 derived. 



Now the human body resembles the body of a higher ape 

 just as the body of the cat resembles that of the dog; and if 

 our ideas as to the relationship between cats and dogs are 

 sound it must follow that apes and men have been gradually 

 developed out of one and the same ancestral species. But 

 we assume that evolution proceeds very slowly — that great 

 changes require millions of years — so that direct evidence of 

 it is impossible to obtain. To get such evidence, indeed, we 



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