CAN WE SEE EVOLUTION OCCURRING? 



the naked ones, are designated by other names. One 

 called Dijfiugia corona (Fig. 1) was selected for observa- 

 tion and breeding. It is a miscroscopic creature about 

 1-1 50th of an inch in diameter. 



These creatures multiply for long periods without any 

 sexual process; that is, each individual divides into halves, 

 and each half then develops into a complete cell, which is 

 later in turn subjected to the same dividing process. Any 

 individual is therefore the offspring of but a single parent; 

 not of two parents, as in the higher animals. The method 

 of reproduction in Difjiugia is shown in Figure 2. A new 

 generation is produced about every two to four days, so 

 that in the course of a year or two many generations may 

 be followed through thousands of descendants produced 

 from one individual. 



Do these thousands of descendants all remain hereditarily 

 alike.'* Or do they gradually and slowly diverge, becoming 

 hereditarily different, as the doctrine of evolution sets 

 forth? 



This was studied by allowing a single individual to repro- 

 duce for many generations, until it had produced thousands 

 of offspring. In the early generations of such an experi- 

 ment, hereditary changes cannot be detected. The offspring 

 often differ from the parents in certain respects, but most 

 of these differences appear not to be inherited. The next 

 generation shows similar differences, but as the genera- 

 tions increase in number we find that certain diversities 

 accumulate and become hereditary. In some descendants the 

 spines become longer; in others they remain shorter. In 

 some the bodies are larger; in others they are smaller. Dif- 

 ferent combinations of size of bodies and of length of spine 

 appear. These differences are inherited. In time from the 

 original single individual a number of diverse stocks have 



[27] 



