94 MODES OF RESEARCH IN GENETICS 



Baltimore, as a population. This may be useful. 

 What we are now considering, though, is knowl- 

 edge about individual cases. 



Let us see what a totally different kind of 

 ability to predict the future event in an individual 

 case is gained when we take into account one 

 single biological fact of an individualistic instead 

 of a statistical character. Suppose, that is to 

 ; say, that we are informed that the mother of the 

 next baby to be born in Baltimore is black. It 

 needs no argument to show how much more 

 precise is our prediction as to the color of the 

 next baby under these conditions. 



This illustration brings out clearly the difference 

 between the two possible bases for the prediction 

 of a future event. On the one hand, such pre- 

 diction may be based on statistical ratios. This 

 means merely a count of an indefinitely large past 

 experience regarding the occurrence or failure of 

 the event, but in no way takes into account the 

 causes which underlie the happening of the event 

 in any particular case. On the other hand, we 

 have the prediction which is based on a definite 

 knowledge of the determinative causes which bring 

 about the happening of a particular individual 

 event of the sort in which we are interested and 

 about which we are to predict. There can be, it 

 would seem, no comparison between the usefulness, 

 in the pragmatic sense, of these two kinds of 

 knowledge. The statistical knowledge on which 



