46 THE THEORY OF NATURAL SELECTION 



gradually sowed and overspread with one kind only, 

 as, for instance, with fennel ; and were it empty of other 

 inhabitants^ it might in a few ages be replenished from 

 one nation only, as, for instance, with Englishmen.' 



Malthus' * Essay ' was first published in 1798, and 

 was subsequently much enlarged. Its author proved 

 incontrovertibly, by a survey of facts gathered from 

 almost all the countries of the world, that human popu- 

 lation tends to increase in a geometrical ratio, and 

 that, consequently, after a time, the less gifted classes 

 of any community are bound to suffer from a stress of 

 poverty, only partly relieved by a high infant mortality, 

 periodic famines, and similar factors, or in less civilized 

 countries by infanticide and other artificial checks. 



Among animals and plants in a state of nature the 

 rate of increase is often very much greater than in the 

 case of the human family, and even where it is not so, 

 unchecked breeding would in a comparatively few years 

 lead to the overpeopling of the earth with the de- 

 scendants of a single pair. As an example of the rate 

 of increase shown by a wild species, we may consider 

 the case of the elephant, instanced by Darwin himself, 

 since this is regarded as being one of the slowest 

 breeders among all known animals. Darwin assumes 

 that the elephant begins breeding at thirty years, and 

 continues to do so until it reaches the age of ninety, 

 bringing forth six young in the interval, and surviving 

 to the age of a hundred. Then, if there were no 

 casualties, he calculates that after from 740 to 750 

 years there would be nearly nineteen million elephants 

 alive descended from the first pair. 



