14 Heredity. 



a complete explanation of tlie origin of species, and that 

 it is exposed to certain Yery serious difficulties. 



Still he concludes that the theory is supported by sucli 

 a mass of evidence that we may fairly believe that our 

 own knowledge, not natural selection, is at fault, and 

 that further research will remove the difficulties by the 

 discovery of other laws. 



Naturalists all over the world have acknowledged the 

 justice of this claim, and some, less candid and broad- 

 minded than Darwin, seem to have even lost sight of the 

 difficulties. 



Now natural selection can act only by the preserva- 

 tion of such variations as chance to appear, and until we 

 know the laws which govern the appearance of variations 

 it must be impossible to decide how far the course of or- 

 ganic evolution has been determined by these unknown 

 laws, and how far by natural selection. 



We may therefore entertain a reasonable hope, that 

 when the true theory of heredity is discovered, it will, 

 by revealing to us the laws and causes of variation^ place 

 the law of natural selection upon a firmer basis, anal show 

 that its apparent difficulties are simply due to the nar- 

 row limits of our knowledge. 



With this introduction I will pass to the discussion of 

 our subject, the nature of heredit}^ 



The attempt to generalize from the whole field of nat- 

 ural science is beset with many difficulties, s'nce the 

 field is so vast that an attempt to give in advance a 

 statement of all the facts upon which reasoning is based 

 would simply confuse the mind of the reader, and bur- 

 den him with a mass of detail. 



It seems best then to start with the generalizations 

 which are believed to bind the facts together, so that the 

 reader may then approach the specific proofs with more 



