386 THE EVOLUTION THEORY 



the complete orgaiiisin, and as soon as a variation would be of 

 advantage it arises — given that it is within the possibilities of the 

 physical constitution of the species. It occurs because its potentialities 

 are already ]Dresent, but it persists and follows a definite course 

 because this is the one that is favoured. In other words, it is 

 primarily fixed by germinal selection alone, but is then preferred by 

 personal selection above the variants running parallel with it. In my 

 opinion the definite direction of the chance germinal variations is 

 determined only by the advantage which it affords to the species with 

 regard to its capacity for existence. But according to Nageli the 

 direction of a variation is quite independent of its utilitj^, which may 

 or may not exist. From Nageli's point of view we could never under- 

 stand the all-prevailing adaptation, but if the utility of a variant is 

 itself sufficient to raise it to the level of a persistent variational 

 tendency, then we understand it. 



Years ago (1883) I compared the species to a wanderer who has 

 before him a vast immeasurable land, through which he is at liberty 

 to choose whatever path he prefers, and in which he may sojourn 

 wherever and for as long as he pleases. But although he may go or 

 stay entirely of his own free will, yet at all times his going or stay- 

 ing will be determined — it must be so and cannot be otherwise — by 

 two factors : first, by the paths available at each place — the variations 

 which crop up — and secondly, b}^ the prospects each of these avail- 

 able paths open up to him. He is striving after a restful place of 

 abode which shall afford him comfortable subsistence, his former 

 home having been spoilt for him Ity increasing expensiveness or too 

 great competition. Even the direction of his first journey will not 

 depend upon chance, since of the many paths available he will, and 

 must, choose that which leads to a habitable and not too crowded 

 spot. If this has been reached — that is to say, if the species has 

 adapted itself to the new conditions — the colonist sets up his abode 

 there, and remains as long as a comfortable existence and a com- 

 petence are secure ; but if these fail him, if grain becomes scarce, or 

 if prices rise, or if a dangerous epidemic breaks out, then he makes 

 up his mind to wander anew, and once more he will choose, among 

 the many available paths, that which offers him the prospect of the 

 speediest and most certain exit from the threatened region, and leads 

 him to another where he may live without risk. There, too, he will 

 remain as long as he is comfortable and not exposed to want or 

 danger, for the species as a whole only becomes transformed when it 

 must. And so it will go on ad riiflidtu'in ; the traveller will, when he is 

 scared away from one dwelling-place, be able to continue his journey in 



