An Introduction to a Biology 



Imagine that I am before you and that I have 12 dice in 

 a dice-box. I shake it and throw them. The result happens 

 to be 7 dice with 4-or-more-bearing faces uppermost. I 

 pick up all the dice, put them back into the dice-box, shake 

 it and throw them again ; the result happens to be 5 such 

 dice. What I want you to observe is that in this pair of 

 throws the two throws which compose it are absolutely inde- 

 pendent of one another ; the result of the second is not 

 affected by the result of the first ; a knowledge of the result 

 of the first does not help us to predict the result of the 

 second. 



Let us think of some way of making the two throws in 

 such a pair dependent, of making the result of the second 

 affected by the result of the first, and of bringing it about 

 that a knowledge of the result of the first shall help us to 

 predict the result of the second. 



I suggest to you that a good way of doing this is to 

 leave half the dice, which formed the first throw, lying on 

 the table, and allow them to form half of the second throw. 

 If I do this, the second throw will consist of six dice lying 

 exactly as they did in the first throw and of six dice thrown 

 afresh. Six of the twelve results which determine the total 



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