EXTINCTION. 349 



conditions were Avhicli checked its incre<ase, whether Roine 

 one or several contingencies, and at what pericxl of tlje 

 horse's life, and in what degree tliey severally acLod. If 

 the conditions had gone on, however slowly, becomii\g less 

 and less favorable, we assuredly should not have perceived 

 the fact, yet the fossil horse would certaiiily have become 

 rarer aiul rarer, and finally extinct — its place being seizx'd 

 on by some more successful competitor. 



It is most difficult always to remember that the increase 

 of every creature is constantly being checked by unper- 

 ceived hostile agencies; and tliat these same unper- 

 ceived agencies are amply sufficient to cause rarity, and 

 fi.ually extinction. So little is this subject understood, 

 that I have heard surprise repeatedly expressed at such 

 great monsters as the Mastodon and the more ancient I)in- 

 osaurians having become extinct; as if mere bodily strength 

 gave victory in the battle of life. Mere size, on the con- 

 trary, would in some cases determine, as has been remarked 

 by Owen, quicker extermination, from the greater amount 

 of requisite food. Before man inhabited India or Africa, 

 some cause must have checked the continued increase of 

 the existing elephant. A highlj capable judge. Dr. Fal- 

 coner, believes that it is chiefly insects which, from inces- 

 santly harassing and weakening the elepliant in India, 

 check its increase; and this was Bruce's conclusion with 

 respect to the African elephant in Abyssinia. It is certain 

 that insects and blood-sucking bats determine the existence 

 of the larger naturalized quadrupeds in several parts of 

 South America. 



We see in many cases in the more recent tertiary forma- 

 tions that rarity precedes extinction; and we know that 

 this has been the progress of events with those animah 

 which have been exterminated, either locally or wliollv, 

 tliroudi man's agency. I may repeat what I i)ul)lished in 

 1845,^namelv, that to admit that species generally become 

 rare before they become extinct— to feel no surpn.-e at the 

 rarity of a species, and yet to marvel greatly when the spe- 

 cies ceases to exist, is much the same as to adnnt that sick- 

 ness in the individual is the forerunner of deatii— to feel 

 no surprise at sickness, but, when the sick man dies, to 

 wonder and to suspect that he died by some deed of 

 violence. 



