170 SECTIONAL ADDRESSES. 



owiug to lack of knowledge of the workiugs of llie hereditary process, 

 merely the visible consequence — the final result of a chain of events. 

 Now, however, that we have made a beginning in our analysis of the 

 stages which culminate in the appearance of any character, a certain 

 looseness becomes apparent in our oi'dinary use of the word Heredity, 

 covering as it does the two concomitant essentials, genetic potentiality 

 and somatic expression — a looseness which may lead us into the para- 

 doxical statement that inheritance is wanting in a case in which never- 

 theless the evidence shows that the genetic constitution of the children 

 is precisely like that of the parents. When we say that a character is 

 inherited no ambiguity is involved, because the appearance of the 

 character entails the inheritance of the genetic potentiality. But when 

 a character is stated not to be inherited it is not thereby indicated whether 

 this result is due to environmental conditions, to genetic constitution, 

 or to both causes combined. That we are now able in some measure 

 to analyse the genetic potentialities of the individual is due to one of 

 those far-reaching discoveries wMch change our whole outlook, and 

 bring immediately in their train a i-apidly increasing array of new facts, 

 falling at once into line with our new conceptions, or by some orderly 

 and constant discrepancy pointing a fresh direction for attack. An 

 historical survey of the steps by which we have advanced to the present 

 state of our knowledge of Heredity has so frequently been given during 

 the last twenty years that the briefest reference to this part of my 

 subject will suffice. 



The earliest attempts to frame some general law which would co- 

 ordinate and explain the observed facts of inheritance were those of 

 Galton and Pearson. Galton's observations led him to formulate two 

 principles which he believed to be capable of general application — the 

 liaw of Ancestral Heredity and the Law of Eegression. The Law of 

 Ancestral Heredity was intended to furnish a general expression for the 

 sum of the heritage handed on in any generation to the succeeding off- 

 spring. Superposed upon the working of this law were the effects of 

 the Law of Eegression, in which the average deviation from the mean 

 of a whole population of any . fraternal group within that population 

 was expressed in terms of the average deviation of tTie parents. These 

 expressions represent statements of averages which, in so far as they 

 apply, hold only when large numbers are totalled together. They afford 

 no means of certain prediction in the individual case. These and all 

 similar statistical statements of the effects of inheritance take no account 

 of the essentially physiological nature of this as of all other processes 

 in the living organism. They leave us unenlightened on the funda- 

 mental question of the nature of the means by which the results we 

 witness came to pass. We obtain from them, as from the melting-pot, 

 various new products whose properties are of interest from other view- 

 points, but, corresponding to no biological reality, they have failed to 

 bring us nearer to our goal — a fuller comprehension of the workings 

 of the hereditary mechanism. Progress in this direction has resulted 

 from the opposite method of inquiry — the study of a single character 

 in a single hne of descent, the method which deals with the unit in 

 place of the mass. The revelation came with the opening of the present 



