Things Are Not What They Used to Be ii 



But most people also accept them without reaHzing that they 

 are assumptions which, from the very nature of things, 

 cannot be proved. If we find a satisfactory cause for an 

 event 999,999 times, we cannot "prove" that things will 

 work the same way the millionth time. 



The principle of uniformity is also a pure assumption, 

 in the sense that it can never be proved. After a million 

 trials we may feel confident, for example, that a pound of 

 lead will take up less space than a pound of marble the next 

 time we have anything to do with lead and marble; but we 

 cannot " prove " that this has always been the case, or that 

 it would be true on Mars, or next year. 



Of course we do not have to make these assumptions 

 if we do not choose to. We do, however, have to be clear 

 about them, as assumptions, when we are discussing evolution 

 (or any other subject for that matter) else we are apt to 

 become confused. 



From these assumptions it follows that any inference 

 we may draw as to past events must be in terms of known 

 materials and forces and relations. The methods of science 

 when applied to the materials of the earth, organic and in- 

 organic, lead to inferences regarding ancient shore lines and 

 glaciers, regarding the antiquity of various structures and 

 formations, regarding the anatomy and even activities of 

 plants and animals that no human being ever saw. The re- 

 sults constitute the descriptive material of evolution. 



Things Are Not What They Used to Be 



If you go away from home for a year, you will find on 

 your return that things are not what they used to be. Even 

 without any special disaster or epidemic, ten to a dozen people 

 out of every thousand have died since you left. Many babies 

 were born in your absence. Some of the houses have burned 

 down, and new ones have been built. The fields and orchards 

 may look the same as they did, but millions of seeds have 

 sprouted; millions of plants have grown to maturity, pro- 



