10 The Common Sense of the Evolution Question 



efforts at understanding, it is not of itself so simple as to 

 " explain " events and experiences automatically. Most of 

 our common thinking about cause and effect is carried on in 

 mechanical terms — push and pull, levers and wheels, ham- 

 mer and tongs, the workings of our common implements 

 and tools. The cause-and-effect relationship of many of the 

 processes going on around us are not as easily restated from 

 the observed facts. A person of ordinary intelligence can 

 understand the working of a pair of shears, or the connection 

 between winding a watch and the movement of the hands. 

 One has to have an exceptional amount of intelligence as 

 well as of special information to understand what connec- 

 tion there is between turning the knob on the radio receiver 

 and " tuning in " for a given broadcasting station. Strictly 

 speaking, nobody understands what connection there is be- 

 tween the properties of common salt and the properties of 

 the two elements, sodium and chlorine, of which it consists. 

 We nevertheless assume that here as in the more familiar 

 experience the principle of causation applies. Nothing 

 happens without a cause and, generally speaking, nothing 

 happens without causing something else to happen. 



Now, any child who gets this notion into his head, and 

 who is also observant enough to see that things around him 

 are different from what they were a few weeks or months 

 ago, will soon come to another common-sense idea. And 

 that is, since everything that happens causes other things to 

 happen, and so on indefinitely, the passing of time will wit- 

 ness a more or less gradual change in all things — faster in 

 some, slower in others, but still a constant and progressive 

 change. 



Assumptions Cannot be Proved 



In our practical affairs and in our reasoning, most of 

 us accept without question these two principles — the princi- 

 ple of causation and the principle of uniformity. We could 

 hardly carry on our daily affairs without accepting them. 



