WHAT EVOLUTION IS 63 



new forms have burst forth? To this 

 question no biologist has a clear and 

 unequivocal answer. It is this uncer- 

 tainty that has been seized upon by a 

 few thoughtless critics who have at- 

 tempted to discredit in the eyes of the 

 general public the well established fact 

 of descent with modification by con- 

 fusing it with the explanations of de- 

 scent. This confusion, commonly due 

 to ignorance, is the source of most of 

 the contentions now met with in evo- 

 lutionary controversies. It does not 

 characterize the clear thinker. Be- 

 cause biologists have not as yet dis- 

 covered how evolution takes place is 

 no reason for denying evolution itself. 

 The explanations of the evolution- 

 ary process thus far offered are large 

 in number. They include, to mention 

 only some of the most important, 

 Lamarck's hypothesis, Darwin's nat- 

 ural selection, Naegeli's idioplasmic 



