43 THE PHYSICAL KINSHIP 



If we knew by actual observation as little con- 

 cerning the evolution of individuals as we do of 

 the evolution of species if we had always been 

 used to seeing animals, including ourselves, in full 

 bloom had never watched the tadpole, the pupa, 

 and the babe pass through their wonderful meta- 

 morphoses on their way to maturity, it would 

 probably be just as hard for many minds to 

 believe that animals evolve individually to be 

 what they are as it is for them to believe that 

 species have grown to be what they are. In the 

 case of individuals, however, the evolution takes 

 place right before our eyes largely, while the 

 evolution of species goes on so slowly and stretches 

 back so far into the past that it can only be 

 inferred. 



Second, the fact that animals, no matter how 

 much they may differ from each other at maturity, 

 all begin existence at the same place. Every 

 animal commences its organic existence as an egg 

 as a one-celled animal as an organism identical 

 in structure with the simplest protozoan. The 

 ova of whales ' are no larger than fern seeds.' 

 The eggs of the coral, the crab, the ape, and the 

 man are so precisely alike that the highest powers 

 of the microscope cannot distinguish between 

 them. 



Third, the fact that the members of the same 

 great group of animals in their individual develop- 

 ment pass through similar stages of evolution. The 

 ' worm ' stage in the development of most insects 

 and the 'fish' stage of frogs are well known. 



