3 io STATISTICAL STUDY OF INHERITANCE 



greatly assisted by crucial experiments — e.g., on the role of 

 atmospheric dust in connection with the precipitation of water 

 vapour. 



Similarly, in regard to the complex facts of inheritance we 

 may pursue the same two methods. We may collect statistics 

 as to the resemblances and differences — e.g. as regards stature, 

 colour of eyes, intellectual ability, in successive generations — 

 and try to arrive at some general induction, which will show 

 the inherent orderliness even in a domain where occurrences 

 seem at first sight as capricious as those of weather. On the 

 other hand, we may focus our attention on the detailed course 

 of events in particular cases — we may inquire, for instance, into 

 the behaviour of the germ-cells before, during, and after ferti- 

 lisation — and try to understand how certain conditions are 

 necessarily followed by certain results. In so doing, we fall 

 back on the general laws of biology, and we are greatly assisted 

 by crucial experiments. 



It is the aim of this chapter to illustrate what has been done 

 by following the statistical method of inquiry into the facts of 

 inheritance, and to state some of the inductions which have 

 rewarded this mode of procedure. As the subject is not an easy 

 one, and as it has been recently discussed by modern masters 

 like Francis Galton and Karl Pearson, and in expository works 

 such as Dr. H. M. Vernon's Variation in Plants and Animals 

 (London, 1903), and Mr. R. H. Lock's Variation, Heredity, and 

 Evolution (London, 1906), we shall confine ourselves to a brief 

 sketch. 



When we have to study results that depend upon numerous 

 complicated conditions, the statistical method is of special 

 service. Not that it can ever tell us how the conditions lead up 

 to the results, but it will tell us what regularity there is in the 

 occurrence of the results, and by displaying some unexpected 

 correlation between certain antecedents and certain results, it 

 may put us on the track of discovering the mechanism that 



