CAN WE SEE EVOLUTION OCCURRING? 



experiments and similar ones on other organisms is given in the 

 author's book "Life and Death, Heredity and Evolution in Uni- 

 cellular Organisms" (R. Badger, Boston, 1920) . An account of 

 racial changes observed in the fruit-fly is given in T. H. Morgan's 

 "Evolution and Genetics." (Princeton Univ. Press, 1925.) 



The evidence of evolution has been read in the rocks and the structures 

 of plants and animals, but under the miscroscope Dr. Jennings is able to 

 follow evolution not as a theory but as a thing that is actually taking place. 

 Intensified study reveals that the hereditary characteristics do become 

 changed by external conditions. Through such diversities, continuing for 

 great numbers of generations, single stocks, uniform in their hereditary 

 characteristics, gradually differentiate into many faintly differing hereditary 

 features. 



In higher organisms the state of knowledge of this point appears less 

 satisfactory. But the evidence, so far as it goes, indicates that processes here 

 are in agreement with those in lower organisms. 



"The organisms whose bodies are condensed into a single cell have, too, 

 a life condensed into a few hours. They present a wonderful opportunity 

 for solving in a brief period some of the deeper problems of life. 



"In a watch glass on our table we may in a week see generations come 

 and go. "We may follow in successive generations the struggle for existence 

 and the results of natural selection. 



"In a few days we may see the birth, babyhood, youth, and age of 

 individuals and their replacement by descendants. We may study the 

 inheritance of parental traits by the new generation or the appearance of 

 new traits. We may observe how the population changes with the passage 

 of ages — all while we wait for one of the changes of the moon. 



"What have the simple organisms to teach us on youth and age, death 

 and rejuvenescence, heredity, variation, evolution?" — Dr. Jennings. 



"In scientific deductions one single divergency suffices to demolish the 

 structure on which they are based." 



Evolution is not a force, but a process; not a cause, but a law. — Lord 

 Morley. 



[33] 



