to form Varieties, 



6303 



others requiring the same kind of food must diminish in proportion. 

 The numbers that die annually must be immense ; and as the indi- 

 vidual existence of each animal depends upon itself, those that die 

 must be the weakest — the very young, the aged, and the diseased, — 

 while those that prolong their existence can only be the most perfect 

 in health and vigour — those who are best able to obtain food regularly, 

 and avoid their numerous enemies. It is, as we commenced by remark- 

 ing, *'a struggle for existence," in which the weakest and least perfectly 

 organized must always succumb. 



Now it is clear that what takes place among the individuals of a 

 species must also occur among the several allied species of a group, — 

 viz., that those which are best adapted to obtain a regular supply of 

 food, and to defend themselves against the attacks of their enemies and 

 the vicissitudes of the 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 counteracting 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 indi- 

 viduals which is the necessary result. 



If now we have succeeded in establishing these two points — 1st, 

 fhat ike animal population of a country is generally stationary, being 

 kept down by a periodical deficiency of food, and other checks ; and, 

 2nd, tliat 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 consideration of varieties, to which the preceding remarks have 

 a direct and very important application. 



Most or perhaps all the variations from the typical form of a species 

 must have some definite effect, however slight, on the habits or 



