34 ON THE TENDENCY OF VAEIETIES TO DEPART 



organization and habits of the various species of ani- 

 mals, and could we measure the capacity of each for 

 performing the different acts necessary to its safety 

 and existence under all the varying circumstances by 

 which it is surrounded, we might be able even to 

 calculate the proportionate abundance of individuals 

 which is the necessary result. 



If now we have succeeded in establishing these 

 two points 1st, that the animal population of a 

 country is generally stationary, being kept down by a 

 periodical deficiency of food, and other checks; and, 

 2nd, that the comparative abundance or scarcity of the 

 individuals of the several species is entirely due to their 

 organization and resulting habits, which, rendering it 

 more difficult to procure a regular supply of food and 

 to provide for their personal safety in some cases than 

 in others, can only be balanced by a difference in the 

 population which have to exist in a given area we 

 shall be in a condition to proceed to the consider- 

 ation of varieties, to which the preceding remarks 

 have a direct and very important application. 



Useful Variations will tend to Increase ; useless or hurt- 

 fid Variations to Diminish. 



Most or perhaps all the variations from the 

 typical form of a species must have some definite 

 effect, however slight, on the habits or capacities of 

 the individuals. Even a change of colour might, by 

 rendering them more or less distinguishable, affect 

 their safety; a greater or less development of hair 



