CHAP. VII. J THEORY OF NATURAL SELECTION. 157 



made by writers who have not taken the trouble to understand 

 the subject. Thus a distinguished German naturalist has asserted 

 that the weakest part of my theory is, that I consider all organic 

 beings as imperfect : what I have really said is, that all are not 

 as perfect as they might have been in relation to their conditions ; 

 and tlu's is shown to be the case by so many native forms in many 

 quarters of the world having yielded their places to intruding 

 foreigners. Nor can organic beings, even if they were at any 

 one time perfectly adapted to their conditions of life, have re- 

 mained so, when their conditions changed, unless they themselves 

 likewise changed ; and no one will dispute that the physical con- 

 ditions 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 advantage to all species, so that 

 he who believes in natural selection " must arrange his genea- 

 logical 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 advan- 

 tages gained through natural selection, survive from year to year 

 by means of its seeds, or ova? Mr. E. Ray Lankester has recently 

 discussed this subject, and he concludes, as far as its extreme 

 complexity 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 reproduc- 

 tion 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 through the modifica- 

 tion of their original types. The many animals which have 

 remained unchanged since the commencement of the glacial period, 

 would have been an incomparably stronger case, for these have 

 been exposed to great changes of climate and have migrated over 

 great distances ; whereas, in Egypt, during the last several thousand 

 years, the conditions of life, as far as we know, ..have remained 

 absolutely uniform. The fact of little or no modification having 

 been effected since the glacial period would have been of some 

 avail against those who believe in an innate and necessary law of 

 development, but is powerless against the doctrine of natural 



