104 DARWINISM AND HUMAN LIFE 



varies, in many cases, as a unity, not in this 

 corner and that — like a machine that is perfected 

 by the accumulation of little patents, — but through 

 and through and all at once. As Darwin pointed 

 out, there is a " correlation of variations." One 

 change brings another in its train, and the one 

 that is for the time most important may evolve 

 another much more important. Thus a variation 

 too small in itself to be of value may be carried 

 over the dead point into effectiveness because it 

 is physiologically bound up with another variation. 



Another aspect of the same idea is that what 

 seem to be new departures in widely separated 

 parts of the animal may be really diverse outcrops 

 of one deep physiological change. We may have 

 thought of this in connection with some disease 

 that we have watched : it has very different 

 expressions in different parts of the body, though 

 it is due to a single slight derangement in the 

 normal sequence of chemical events. We may 

 have thought of the same idea in connection 

 with sex, where changes apparently confined 

 to minute and superficial and unconnected parts 

 may be, as it were, the correlated outcrop of 

 one deep physiological change.^ It is a famihar 

 fact that numerous apparently distant and un- 

 connected changes of adolescence are all funda- 

 mentally one. Similarly, when an individual plant 

 or animal varies as a whole, when compared with 

 its parent, this means that the potential individual, 

 the germ-cell, has varied as a imity. 



(4) Brusque Variations more Frequent than 

 was formerly supposed. — But the most important 



1 " The Evolution of Sex," by P. Geddes and J. Arthur Thomson, 

 "Contemporary Science Series " (1889). Bevised Edition (1001). 



