EXCESSIVE FECUNDITY 5 



at this rate in less than a thousand years there would literally 

 not be standing-room for his progeny. Linnaeus has calculated 

 that if an annual plant produced only two seeds — and there is 

 no plant so unproductive as this — and their seedlings next year 

 produce two, and so on, then in twenty years there would be a 

 million plants. The elephant is reckoned the slowest breeder 

 of all known animals, and I have taken some pains to estimate 

 its probable minimum rate of natural increase ; it will be safest 

 to assume that it begins breeding when thirty years old, and goes 

 on breeding till ninety years old, bringing forth six young in the 

 interval, and surviving till one hundred years old. If this be 

 so, after a period of from 740 to 750 years there would be nearly 

 19,000,000 elephants aUve, descended from the first pair." ^ 



Given this enormous fecundity, it is evident that, unless 

 Nature counteracts it by means of an equally enormous elimina- 

 tion, the number of organisms in the world would very soon be 

 too great for the world to contain, for space, air, and food are 

 limited. A definite and constant balance between the rate of 

 multiplication and the rate of elimination must therefore be 

 established. The total number of individuals of a species living 

 in a given space is certainly subject to variation — ^in certain cases 

 it is extremely variable — but we must, nevertheless, accept the 

 fact that the average number of the members of a species remains 

 constant. Otherwise, if the conditions remain the same, the 

 species would be doomed to speedy annihilation. The number of 

 deaths in a city during one year may be 50,000, in another year 

 45,000, in the third year 48,000. The total varies, but the 

 average number of the inhabitants maintains itself, and must 

 maintain itself if the city in question is not to disappear. Of 

 course, if the conditions are greatly altered, greatly increased 

 population may become possible and normal. 



If we call the average numerical strength of a given species 

 under given conditions the normal number of that species, the 

 ' Darwin, The Origin of Species, pp. 79, 80 (edition 1902) 



