CAN WE SEE EVOLUTION OCCURRING? 



ing the characteristics illustrated by their representatives in 

 the figure. A single stock, derived by fission from a single 

 parent, has gradually diversified itself into many stocks that 

 are hereditarily different. 



What the doctrine of evolution asserts is therefore true 

 for Difflugia. It does gradually transform and produce new 

 races. If this is what evolution means, we have here seen 

 evolution occurring. 



A number of other lower organisms have been studied in 

 a similar way, and with similar results. They do not remain 

 entirely constant. Although the process is excessively slow, 

 they gradually transform into hereditarily diverse races, in 

 accordance with the doctrine of evolution. 



To observe such changes in higher animals and' plants is 

 much more difficult. Each generation requires a longer 

 time; in a human life few can be observed. But a greater 

 difficulty lies in the fact that most of the higher organisms 

 reproduce from two parents. The two parents always differ 

 in their hereditary constitution, so that the offspring are 

 usually a combination of two hereditarily diverse stocks. 

 In forming that combination, each parent loses half of its 

 genes — that is, half of the thousand different chemicals on 

 which depend the way it develops and its later characteristics. 

 The remaining halves from the two parents then unite to 

 form a new combination of genes, from which the offspring 

 develops. For every single offspring the process is repeated, 

 but in each case it is a different set of genes that is lost 

 from each parent, a different set that remains. Consequently 

 through the union of the two remaining halves there is in 

 every case a new and diverse combination of the genes pro- 

 duced; so that every one of the offspring of a pair of parents 

 differs in its hereditary constitution from every other one; 



[29] 



