ORIGIN OF THE SPECIFIC TYPE 331 



have to adapt themselves ma,y be thought of as the distant goal, 

 and the processes in the germ-plasm which give rise to variation in 

 a definite direction may be compared to numerous human beings 

 scattered irregularly over the surface of the snow. If the sleigh 

 receives from one of these a push which chances to be in the direction 

 of the goal, it rushes on towards this and ultimately reaches it if the 

 person pushing continues to push in the same direction. So far, then, 

 it seems as if the transformation of the part concerned depended upon 

 germinal selection alone, but we must not forget that the germ-plasm 

 does not contain only one determinant for every part of the body, but 

 as many determinants as there are ids. We must therefore increase 

 the number of our sleighs, and now it is obvious that the pushers of 

 the sleighs, that is, germinal selection, may push one sleigh on toward 

 the goal, but others in the opposite or in any other direction. If we 

 assume that all the sleighs which have taken a wrong direction must 

 reach dangerous ground, and ultimately plunge into an abyss, but 

 that from a neighbouring point sleighs were being dispatched to 

 replace all that came to grief, that these in their turn might attempt 

 to reach the goal, it would ultimately come about that the requisite 

 number of sleighs would arrive at the goal — that is to say, that the 

 new adaptation would be attained. 



The abysses represent the elimination of the less favourable 

 variational tendencies, and the constant replacing of sleighs represents 

 the intermingling of fresh ids through amphimixis. If all the sleighs 

 run in the wrong direction they all come to grief, that is, the individual 

 concerned is eliminated with all the ids of its germ-plasm — it dis- 

 appears altogether from the ranks of the species. But if only 

 a portion of them run in the right direction, care is taken that in 

 following generations, that is, in the continuation of the sleigh-race, 

 this portion combines with those of another group which are also 

 running in the right direction — that is, with the half number of ids 

 from another germ-plasm in amphimixis. 



It is not possible to follow the analogy further, but perhaps it 

 may serve to illustrate how germinal selection may be the only 

 impelling force in the organisms, and yet only a small part of its 

 results are determined by itself, and by far the larger part by external 

 conditions. We understand how a variation in a definite direction 

 can exist, and yet it is not that which creates species, genera, orders, 

 and classes; it is the selection and combination of the variational 

 tendencies by the conditions of life, which occurs at every step. There 

 was no variational tendency leading from terrestrial mammals to 

 Cetaceans, but there was a variational tendency moving the nostrils 



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