DIYERGENGE OF CIIAllACTEH. io3 



ferior animals with intermediate characters, being neither 

 very swift nor very strong, would not have been used for 

 breeding, and will thus have tended to disappear. Here, 

 then, we see in man's productions the action of what may be 

 called the principle of divergence, causing differences, at 

 first barely appreciable, steadily to increase, and the breeds 

 to diverge in character, both from each other and from 

 their common parent. 



But, how, it may be asked, can any analogous principle 

 apply in nature? I believe it can and does apply most 

 etficiently (though it was a long time before I saw how), 

 from the simple circumstance that the more diversified the 

 descendants from any one species become in structure, 

 constitution and habits, by so much will they be better 

 enabled to seize on many and widely diversified places in 

 the polity of nature, and so be enabled to increase in 

 numbers. 



We can clearly discern this in the case of animals with 

 simple habits. Take the case of a carnivorous quadruped, 

 of which the number that can be supported in any country 

 has long ago arrived at its full average. If its natural 

 power of increase be allowed to act, it can succeed in in- 

 creasing (the country not undergoing any change in con- 

 ditions) only by its varying descendants seizing on places 

 at present occupied by other animals: some of them, for 

 instance, being enabled to feed on new kinds of prey, 

 either dead or alive; some inhabiting new stations, climb- 

 ing trees, frequenting water, and some perhaps becoming 

 less carnivorous. The more diversified in habits and 

 structure the descendants of our carnivorous animals 

 become, the more places they will be enabled to occupy. 

 What applies to one animal will apply throughout all time 

 to all animals — that is, if they vary — for otherwise natural 

 selection can effect nothing. So it will be with plants. It 

 has been experimentally proved, that if a plot of ground 

 be sown with one species of grass, and a similar plot be 

 sown with several distinct genera of grasses, a greater 

 number of plants and a greater weight of dry herbage can 

 be raised in the latter than the former case. The same has 

 been found to hold good when one variety and several mixed 

 varieties of wheat have been sown on equal spaces of 

 ground. Hence, if any one species of grass were to go on 



