102 Darwin- Wallace Celebration. 



seasons, must necessarily obtain and preserve a superiority 

 in population ; while those species which from some defect 

 of power or organization are the least capable of counteract- 

 ing the vicissitudes of food supply, &c., must diminish in 

 numbers, and, in extreme cases, become altogether extinct. 

 Between these extremes the species will present various 

 degrees of capacity for ensuring the means of preserving, 

 life ; and it is thus we account for the abundance or rarity 

 of species. Our ignorance will generally prevent us from 

 accurately tracing the effects to their causes ; but could we 

 become perfectly acquainted with the organization and habits 

 of the various species of animals, 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 %>rovide 

 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 

 consideration of varieties, t0 which the preceding remarks 

 have a direct and very important application. 



Most or perhaps all the variations from the typical form o 

 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 

 might modify their habits. More important changes, such 

 as an increase in the power or dimensions of the limbs or any 

 of the external organs, would more or less affect their mode 

 of procuring food or the range of country which they inhabit. 

 It is also evident that most changes would affect, either 

 favourably or adversely, the powers of prolonging existence. 

 An antelope with shorter or weaker legs must necessarily 

 suffer more from the attacks of the feline carnivora ; the 

 passenger pigeon with less powerful wings would sooner or 

 later be affected in its powers of procuring a regular supply 

 of food ; and in both cases the result must necessarily be a 



