88 



Divergence of Character. Chap. iv. 



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 carnivorous. The more 

 divers'ified in habits and structure the descendants of our carnivo- 

 rous 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 experi- 

 mentally 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 

 countless 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, especially if 

 freely open to immigration, and where the contest between indivi- 

 dual 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 each other. So 

 it is with the plants and insects on small and uniform islets: also 

 in small ponds of fresh water. Farmers find that they can raise 

 most food by a rotation of plants belonging to the most different 

 orders : nature follows what may be called a simultaneous rotation. 

 Most of the animals and plants which live close round any small 





