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. 
