EXTINCTION OF SPECIES. 435 



a species may have been originally adapted to exist in, will 

 militate against that existence in a degree proportionate to 

 the bulk of the species. If a dry season be gradually pro- 

 longed, the large Mammal will suffer from the drought sooner 

 than the small one ; if such alteration of climate affect the 

 quantity of vegetable food, the bulky Herbivore will first feel 

 the effects of stinted nourishment; if new enemies be intro- 

 duced, the large and conspicuous animal will fall a prey, 

 while the smaller kinds conceal themselves and escape. Small 

 quadrupeds are more prolific than large ones. Those of the 

 bulk of the Mastodons, Megatheres, Glyptodons, and Diproto- 

 dons are uniparous. The actual presence, therefore, of small 

 species of animals in countries where larger species of the 

 same natural families formerly existed, is not the consequence 

 of degeneration — of any gradual diminution of the size of such 

 species — but is the result of circumstances which may be il- 

 lustrated by the fable of the "oak and the reed ;" the smaller 

 animals have bent and accommodated themselves to changes 

 to which the larger species have succumbed. 



That species, or forms so recognized by their distinctive 

 characters and the power of propagating them, have ceased to 

 exist, and have successively passed away, is a fact no longer 

 questioned. That they have been exterminated by exceptional 

 cataclysmal changes of the earth's surface has not been proved. 

 That their limitation in time, in some instances or in some 



dition of things, if followed out to its full consequences, seems to lead only 

 to my original inference, viz., an extinction of species ; for, when the hares 

 were all destroyed the long-legged dogs would perish. At most there could 

 but be a reversion to the first form and conditions. For, as the hares 

 decreased in number, that of the rabbits would increase ; the changes of 

 organization that fitted the dogs for catching hares being such as would detract 

 from their power of unearthing rabbits. A variety with a shorter and stronger 

 foot might arise, and would be the first to profit by the preponderance of the 

 burrowing rodents. The individual dogs with the strongest and shortest limbs, 

 let the difference be ever so small, would be slightly favoured, live longer, rear 

 more young inheriting the rabbit-catching peculiarities ; the less fossorial varie- 

 ties would be rigidly destroyed, etc. It is an argument in a circle. 



