CAN WE SEE EVOLUTION OCCURRING? 



the circle; yet men have discovered this fact and have meas- 

 ured the present rate of the motion. The fixed stars are 

 not in fact fixed in their relation to one another; slight 

 changes of position occur, some of them requiring centuries 

 for detection; yet men have detected them. Certain radio- 

 active substances disintegrate so slowly that it requires mil- 

 lions of years for a given portion to transform, yet the 

 changes have been detected and their rate has been measured. 

 If we can detect these things why should we not be able to 

 detect — to catch in progress — the changes that we call evolu- 

 tion? We cannot directly see the growth of a tree, but by 

 taking photographs at intervals and running them through 

 a moving picture machine we can see the tree grow, and 

 we can determine how its growth occurs. Ought we not 

 to be able to get some sort of a moving picture of evolu- 

 tionary change? 



The task is bound to be difficult. The process of evolu- 

 tion is complex. Evolutionary changes move in many dif- 

 ferent directions. Some organisms degenerate; others grow 

 more complex and become adapted to more varied condi- 

 tions; still others change hardly at all. The process cannot 

 be uniform ; it produces diversity, not simplicity. What sort 

 of changes should we expect to find if we could watch certain 

 organisms closely enough to see the evolutionary changes 

 that occur in them during a human lifetime? 



We should have to study some organism that produces 

 many generations while man passes through but one. For- 

 tunately, there are many such organisms — creatures that 

 produce a new generation every day or every few days. We 

 should have to begin with a single individual and follow 

 its offspring for many generations, obtaining great numbers 

 of descendants. According to the theory of evolution, slight 

 changes would occur as the generations pass. These changes 



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