What Is a Fish? 13 



dividing itself up into separate forms. The rainbow trout 

 has become the golden trout in the isolation of the high 

 mountains. The salmon of the Atlantic has become the steel- 

 head trout of the Pacific or vice versa, and if, as one au- 

 thority states, there is no single external feature by which 

 all members of these two species can at all times be told 

 apart, then it is clear that the number of dead forms inter- 

 vening between the two is just about zero. 



Finally, it must be pointed out that, in spite of all that 

 has been said, it is not compulsory to believe in evolution. 

 Up to eighty years ago, most people had never heard of it, 

 and they were just as happy as they are now. To be sure, 

 three or four men, including the old Swedish naturalist 

 Linnaeus back in the eighteenth century, had gone sniffing 

 around the theory, picking at the wrappings that hid it, get- 

 ting an intriguing but unrevealing glimpse of one part or 

 another of it, but quite unable to understand what it was all 

 about, to see it as a whole. That has often been the way when 

 some new and universal principle was about to be revealed to 

 the world. Then suddenly two Englishmen, one in Kent and 

 one in Malaya, lifted the veil at the same time, one as a 

 result of long and painstaking piecing together of fact and 

 theory, the other as a result of a sudden brilliant inspiration j 

 and it is because the younger man, with a generosity for- 

 tunately sometimes found among scientists, recognized that 

 his lucky guess could not justifiably be placed on a par with 

 the other man's far-reaching labor of synthesis, that the 

 name of Charles Darwin, and not that of Alfred Russell 

 Wallace, is taught to school children today as the founder 

 of the theory of evolution. 



Fish, then, are backboned animals which live In the water, 

 breathe through gills, and have fins. As usual, there are ex- 

 ceptions. Some breathe with lungs, and some have no recog- 

 nizable fins. Lung-fish and eels are fishes, but whales and 



