THE FACTS AND LAWS OF VAKTATTOy 47 



discovered. For, whatever be said to the contrary, 

 the two sexes, from the biological point of view, arc 

 strictly equal and complementary. 



CHAPTER V 



THE FACTS AND LAWS OF VARIATION 



A CHAPTER is formally devoted to this subject simply 

 for the sake of emphasis. The reader has already 

 seen that in discussion of strict correlatives, such as 

 heredity and variation, the two cannot be dissociated, 

 since each implies the other. Thus in the preceding 

 and following chapters we find as much to say of 

 variation as of heredity. But the emphasis of a 

 separate chapter may be of use in enabling us fully 

 to appreciate the conclusion which has been reached 

 by the a loosteriori study of variation. 



We have already argued that certain current ways 

 of looking at variation are untenable. Not concern- 

 ing ourselves with the detailed facts that may be 

 observed, we have argued deductively from certain 

 principles that variations cannot be regarded as 

 arbitrary or as outside the law of causation, or as 

 incalculable or as accidental lapses on the part of the 

 law of heredity, and that, as believers in the Uni- 

 formity of Nature, we must hold to our view in spite 

 of appearances. 



But the fact here to be insisted upon is that 

 " appearances " are for us and not against us. We 

 find that when we come systematically to study the 

 facts of variation, they are not arbitrary or incalcul- 



