Chap. HX] GEOMETKICAL KATIO OF INCKEASE. 81 



of the animals or plants has been suddenly and 

 temporarily increased in any sensible degree. The 

 obvious 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 

 extraordinarily 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 

 animals tends, I think, to mislead us : we see no great 

 destruction 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 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 



