104 THE ORIGIN OF SPECIES 



of species? The amount of life (I do not mean the number of 

 specific forms) supported on an area must have a limit, depend- 

 ing so largely as it does on physical conditions; therefore, if an 

 area be inhabited by very many species, each or nearly each species 

 will be represented by few individuals; and such species will be 

 liable to extermination from accidental fluctuations in the nature 

 of the seasons or in the number of their enemies. The process of 

 extermination in such cases would be rapid, whereas the produc- 

 tion of new species must always be slow. Imagine the extreme case 

 of as many species as individuals in England, and the first severe 

 winter or very dry summer would exterminate thousands on thou- 

 sands of species. Rare species, and each species will become rare if 

 the number of species in any country becomes indefinitely in- 

 creased, will, on the principle often explained, present within a 

 given period few favorable variations; consequently, the process 

 of giving birth to new specific forms would thus be retarded. When 

 any species becomes very rare, close interbreeding will help to 

 exterminate it; authors have thought that this comes into play in 

 accounting for the deterioration of the aurochs in Lithuania, of 

 red deer in Scotland, and of bears in Norway, etc. Lastly, and this 

 I am inclined to think is the most important element, a dominant 

 species, which has already beaten many competitors in its own 

 home, will tend to spread and supplant many others. Alph. de 

 Candolle has shown that those species which spread widely tend 

 generally to spread very widely, consequently they will tend to 

 supplant and exterminate several species in several areas, and thus 

 check the inordinate increase of specific forms throughout the 

 world. Dr. Hooker has recently shown that in the south-east corner 

 of Australia, where, apparently, there are many invaders from dif- 

 ferent quarters of the globe, the endemic Australian species have 

 been greatly reduced in number. How much weight to attribute to 

 these several considerations I will not pretend to say; but con- 

 jointly they must limit in each country the tendency to an indef- 

 inite augmentation of specific forms. 



SUMMARY OF CHAPTER 



If under changing conditions of life organic beings present indi- 

 vidual differences in almost every part of their structure, and this 

 cannot be disputed; if there be, owing to their geometrical rate 

 of increase, a severe struggle for life at some age, season, or year, 

 and this certainly cannot be disputed; then, considering the in- 

 finite complexity of the relations of all organic beings to each other 

 and to their conditions of life, causing an infinite diversity in 



