Chap. 111.] GEOMETRICAL RATIO OP INCREASE. 81 



the animals or plants has been suddenly and tem- 

 porarily increased in any sensible degree. The ob- 

 vious explanation is that the conditions of life have 

 been highly favourable, and that there has consequently 

 been less destruction of the old and young, and that 

 nearly all the young have been enabled to breed. 

 Their geometrical ratio of increase, the result of which 

 never fails to be surprising, simply explains their ex- 

 traordinarily rapid increase and wide diffusion in their 

 new homes. 



In a state of nature almost every full-grown plant 

 annually 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 rapidly stock every station in which they could 

 anyhow exist, — and that this geometrical tendency to 

 increase must be checked by destruction at some period 

 of life. Our familiarity with the larger domestic ani- 

 mals tends, I think, to mislead us: we see no great de- 

 struction falling on them, but we do not keep in mind 

 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 an- 

 nually 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 favour- 

 able 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 



