Chap. VII.] THEORY OF NATURAL SELECTION. 263 



they were at any one time perfectly adapted to their con- 

 ditions of life, have remained so, when their conditions 

 changed, unless they themselves likewise changed 

 and no one will dispute that the physical conditions of 

 each country, as well as the numbers and kinds of its 

 inhabitants, have undergone many mutations. 



A critic has lately insisted, with some parade of 

 mathematical accuracy, that longevity is a great advan- 

 tage to all species, so that he who believes in natural 

 selection " must arrange his genealogical tree " in such 

 a manner that all the descendants have longer lives 

 than their progenitors ! Cannot our critic conceive that 

 a biennial plant or one of the lower animals might range 

 into a cold climate and perish there every winter ; and 

 yet, owing to advantages gained through natural selec- 

 tion, survive from year to year by means of its seeds or 

 ova ? Mr. E. Eay Lankester has recently discussed this 

 subject, and he concludes, as far as its extreme com- 

 plexity allows him to form a judgment, that longevity 

 is generally related to the standard of each species in 

 the scale of organisation, as well as to the amount of 

 expenditure in reproduction and in general activity. 

 And these conditions have, it is probable, been largely 

 determined through natural selection. 



It has been argued that, as none of the animals and 



plants of Egypt, of which we know anything, have 



changed during the last three or four thousand years, 



so probably have none in any part of the world. But, 



as Mr. G. H. Lewes has remarked, this line of argument 



proves too much, for the ancient domestic races figured 



on the Egyptian monuments, or embalmed, are closely 



similar or even identical with those now living ; yet all 



naturalists admit that such races have been produced 

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