138 ECONOMIC MAMMALOGY 



nent ice of that inhospitable region. Now the whole group of elephants 

 is entirely extinct over the greater part of its former range. The 

 sloth family, once represented by gigantic ground sloths in portions 

 of the United States, is now represented only by the much smaller tree 

 sloths of South America. These are but a few of the multitude of ex- 

 amples that might be cited to show that mammalian life has long been 

 dwindling, large groups becoming extinct and no new ones developing 

 to replace them. Quite possibly there are just as many species and 

 individuals still living as at any time in the past, but that would be 

 because of the small rodents, such as mice and their allies, of which 

 there are very numerous species and vast hordes of individuals. 



Probably under natural conditions of the past the development and 

 extinction of species and higher groups proceeded in a slow and orderly 

 fashion. It is very probable that at no time during the past ages have 

 such faunal changes been wrought within a short time as within the 

 past century or two. This is due to the rapid development and spread 

 of civilization and the rapid increase in human population. A large 

 amount of destruction of wild life was unavoidable, as agriculture and 

 stock-raising on a large scale developed, but much that was unneces- 

 sary was made possible by the invention of more efficient modern 

 weapons, placed in the hands of thoughtless and selfish human beings. 

 In ordinary times under natural conditions the mortality of all species 

 of mammals just about balances the birth rate. If the mortality of a 

 species much exceeded the birth rate, it would not long be able to 

 maintain its existence, but would dwindle away to extinction. If the 

 mortality fell very far below the birth rate, in time the species would 

 become so abundant as to be self-destructive through competition for 

 food. Modern man, having stepped in and changed the face of nature 

 by wholesale and widespread agricultural operations and the destruc- 

 tion of forests, and invented deadly, rapid-fire guns, placing all these 

 in the balance on the side of destruction, the larger animals have little 

 chance for survival unless something equally effective be done to even 

 up the balance, and this has not yet been done. 



It has been said that man, who complains of the destructiveness of 

 certain species of rodents, is himself the most destructive animal. No 

 other animal has exterminated so many species of other animals or 

 been so generally destructive to nature in its various aspects. Dr. Os- 

 borne, in his Foreword to Hornaday's timely book, Our Vanishing 

 Wild Life, says, among other things: 



