LORD SALISBURY ON EVOLUTION. 577* 



tongued will fail where a number of the longer-tongued succeed. 

 As every creature multiplies up to the limits set by the means of 

 subsistence, herds of giraffes must be from time to time under- 

 fed. At such times the short-tongued ones must be more under- 

 fed than the long-tongued ones. The difference of feeding may 

 not be such as to produce in a direct way greater mortality in the 

 one class than in the other, but it may readily tell indirectly. 

 Especially will there be more deaths of the weaker adults, and 

 the less vigorous young they have produced, when the herd is 

 chased by carnivores. Those which are a yard or two behind the 

 rest lose their lives ; and a very small defect in the constitutional 

 state of the adults, or the strength of the young, may entail the 

 slight difference in speed implied. So that, other things equal, 

 more of the short-tongued and their offspring will die than of the 

 long-tongued and their offspring. Hence, without any special 

 choice of mates, it will result that in the next generation the aver- 

 age of length of tongue will be greater. Through subsequent 

 generations the same process will go on increasing this advan- 

 tageous variation, until some limit is reached at which disadvan- 

 tages check it, or at which the life- sustaining advantages from 

 some other variation become greater. 



So that in the absence of any such improbable events as those 

 Lord Salisbury supposes to be necessary, there are two co-operat- 

 ing ways in which survival of the fittest establishes in a species a 

 useful modification of structure. 



The great length of time required for the production of species 

 by the evolutionary process, is supposed by Lord Salisbury to 

 furnish a reason for disbelief. In support of his argument he 

 cites Lord Kelvin's conclusion that life can not have existed on 

 the Earth more than a hundred millions of years. Respecting 

 Lord Kelvin's estimate it may be remarked that the truth of a 

 conclusion depends primarily on the character of the premises ; 

 that mathematical processes do not furnish much aid in the 

 choice of premises ; that no mathematical genius, however trans- 

 cendent, can evolve true conclusions out of premises that are 

 either incorrect or incomplete ; and that while putting absolute 

 faith in Lord's Kelvin's reasonings, it is possible to doubt the 

 data with which he sets out. Suppressing criticism, however, let 

 us accept in full the hundred million years, and see what comes 

 of it. Lord Salisbury argues : 



" If we think of that vast distance over which Darwin conducts us, from 

 the jelly-fish lying on the primeval heach to man as we know him now ; 

 if we reflect that the prodigious change requisite to transform one into the 

 other is made up of a chain of generations, each advancing by a minute 

 variation from the form of its predecessor, and if we further reflect that 



TOL, XLVIII. 41* 



