44 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 



regard it as by no means absolutely necessary to that trans- 

 formation. 



Lastly, although I ascribe to sexual combination, with and 

 without the help of selection, an important influence in the 

 moulding of species, yet it cannot be granted that this 

 influence is essentially paramount, or even that it is thoroughly 

 independent in its action, if we start from the assumption 

 that sexual differentiation is itself at first an acquired 

 character. 



In reality its own beginnings are to be traced to external in- 

 fluences, and obviously it continues to serve as the means for the 

 transmission and distribution of other characters acquired by 

 the body in difterent localities under different conditions. In 

 that it unites, combines different elements, it can engender a 

 new third element (crossing). Without this mixture of what 

 is foreign — different, however, through the continued union of 

 the cognate, it leads ultimately on the contrary to equalisation, 

 not to progress. 



Thus sexual combination, like the principle of utility, can 

 only work with the material which phyletic growth offers to 

 it ; universally something new must first exist before either 

 can commence to operate. 



I years ago expressed my belief that the original directions 

 of evolution are shown by the facts to have been followed with 

 an extraordinary persistence ; let the external influences be 

 what they will, the new directions never seem to radiate from 

 the starting-point of modification — the new lines pass off at 

 an acute anc'le, at first near the original ones — onlv the 

 intermittent deviation caused by correlation forms an excep- 

 tion. But the fact of evolution in a definite direction is 

 explained neither by selection nor by sexual combination by 

 itself 



I proceed now to the closer consideration of one of the 

 most important of the causes to which I have attributed the 



