Chap. III. HIGH RATE OF INCREASE. 65 



of the plants now most numerous over the wide plains of 

 La Plata, clothing square leagues of surface almost to 

 the exclusion of all other plants, have been introduced 

 from Europe ; and there are plants which now range in 

 India, as I hear from Dr. Falconer, from Cape Comorin 

 to the Himalaya, which have been imported from America 

 since its discovery. In such cases, and endless instances 

 could be given, no one supposes that the fertility of 

 these animals or plants has been suddenly and tempo- 

 rarily increased in any sensible degree. The obvious 

 explanation is that the conditions of life have been very 

 favourable, and that there has consequently been less 

 destruction of the old and young, aud that nearly all the 

 young have been enabled to breed. In such cases the 

 geometrical ratio of increase, the result of which never 

 fails to be surprising, simply explains the extraordinarily 

 rapid increase and wide diffusion of naturalised produc- 

 tions 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 aud animals are tending to increase at a geo- 

 metrical ratio, that all would most rapidly stock every 

 station in which they could any how 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 



