4 The Problems 



cases the sudden appearance of highly prepotent forms, 

 and the like. We are now passing out of that stage. 

 It is not that the interest of particular cases has in 

 any way diminished for such records will always have 

 their value but it has become likely that general ex- 

 pressions will be found capable of sufficiently wide appli- 

 cation to be justly called "laws " of heredity. That this 

 is so was till recently due almost entirely to the work of 

 Mr F. Galton, to whom we are indebted for the first 

 systematic attempt to enuntiate such a law. 



All laws of heredity so far propounded are of a 

 statistical character and have been obtained by statistical 

 methods. If we consider for a moment what is actually 

 meant by a "law of heredity'' we shall see at once why 

 these investigations must follow statistical methods. For 

 a "law' of heredity is simply an attempt to declare 

 the course of heredity under given conditions. But if 

 we attempt to predicate the course of heredity we have 

 to deal with conditions and groups of causes wholly 

 unknown to us, whose presence we cannot recognize, 

 and whose magnitude we cannot estimate in any par- 

 ticular case. The course of heredity in particular cases 

 therefore cannot be foreseen. 



Of the many factors which determine the degree 

 to which a given character shall be present in a given 

 individual only one is usually known to us, namely, 

 the degree to which that character is present in the 

 parents. It is common knowledge that there is not that 

 close correspondence between parent and offspring which 

 would result were this factor the only one operating ; 

 but that, on the contrary, the resemblance between the 

 two is only an uncertain one. 



In dealing with phenomena of this class the study 



