82 DIVERGENCE OF CHARACTER. [CHAP. IV. 



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 increasing (the country not under- 

 going any change in conditions) 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, climbing 

 trees, frequenting water, and some perhaps becoming less carni- 

 vorous. The more diversified in habits and structure the descend- 

 ants 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 in 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 varying, and the varieties were continually 

 selected which differed from each other in the same manner, 

 though in a very slight degree, as do the distinct species and 

 genera of grasses, a greater number of individual plants of this 

 species, including its modified descendants, would succeed in 

 living on the same piece of ground. And we know that each 

 species and each variety of grass is annually sowing almost count- 

 less seeds ; and is thus striving, as it may be said, to the utmost 

 to increase in number. Consequently, in the course of many 

 thousand generations, the most distinct varieties of any one 

 species of grass would have the best chance of succeeding and of 

 increasing in numbers, and thus of supplanting the less distinct 

 varieties ; and varieties, when rendered very distinct from each 

 other, take the rank of species. 



The truth of the principle that the greatest amount of life can 

 be supported by great diversification of structure, is seen under 

 many natural circumstances. In an extremely small area, especi- 

 ally if freely open to immigration, and where the contest between 

 individual and individual must be very severe, we always find 

 great diversity in its inhabitants. For instance, I found that a 

 piece of turf, three feet by four in size, which had been exposed 

 for many years to exactly the same conditions, supported twenty 

 species of plants, and these belonged to eighteen genera and to 

 eight orders, which shows how much these plants differed from 



