STRUGGLE FOR EXISTENCE 61 



explains the extraordinarily rapid increase and wide 

 diffusion of naturalised productions in their new homes. 



In a state of nature almost every plant produces seed, 

 and amongst animals there are very few which do not 

 annually pair. Hence we may confidently assert, that 

 all plants and animals are tending to increase at a 

 geometrical ratio, that all would most rapidly stock 

 every station in which they could anyhow exist, and 

 that the geometrical tendency to increase must be 

 checked by destruction at some period of life. Our 

 familiarity with the larger domestic animals tends, 

 I think, to mislead us : we see no great destruction 

 falling on them, and we forget that thousands are 

 annually slaughtered for food, and that in a state of 

 nature an equal number would have somehow to be 

 disposed of. 



The only difference between organisms which annually 

 produce eggs or seeds by the thousand, and those which 

 produce extremely few, is, that the slow-breeders would 

 require a few more years to people, under favourable 

 conditions, a whole. district, let it be ever so large. 

 The condor lays a couple of eggs and the ostrich a score, 

 and yet in the same country the condor may be the 

 more numerous of the two : the Fulmar petrel lays 

 but one egg, yet it is believed to be the most numerous 

 bird in the world. One fly deposits hundreds of eggs, 

 and another, like the hippobosca, a single one ; but 

 this difference does not determine how many indi- 

 viduals of the two species can be supported in a district. 

 A large number of eggs is of some importance to those 

 species which depend on a rapidly fluctuating amount 

 of food, for it allows them rapidly to increase in 

 number. But the real importance of a large number 

 of eggs or seeds is to make up for much destruction 

 at some period of life ; and this period in the great 

 majority of cases is an early one. If an animal can in 

 any way protect its own eggs or young, a small number 

 may be produced, and yet the average stock be fully 

 kept up; but if many eggs or young are destroyed, many 

 must be produced, or the species will become extinct 



