Chap. IV.] SUMMARY. 159 



have thought that this comes into play in accounting 

 for the deterioration of the Aurochs in Lithuania, of 

 Bed Deer in Scotland, and of Bears in Norway, &c. 

 Lastly, and this I am inclined to think is the most im- 

 portant 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 S.E. comer 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 conjointly they must 

 limit in each country the tendency to an indefinite aug- 

 mentation of specific forms. 



Summary of Chapter. 



If under changing conditions of life organic beings 

 present individual 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 in- 

 finite diversity in structure, constitution, and habits, to 

 be advantageous to them, it would be a most extraor- 



