58 THE ORIGIN OF SPECIES 



It has been suggested that moths may fertilize the clovers; but I 

 doubt whether they could do so in the case of the red clover, from 

 their weight not being sufficient to depress the wing petals. Hence 

 we may infer as highly probable, that, if the whole genus of 

 humble-bees became extinct or very rare in England, the heart's- 

 ease and red clover would become very rare, or wholly disappear. 

 The number of humble-bees in any district depends in a great 

 measure upon the number of field-mice, which destroy their combs 

 and nests; and Colonel Newman, who has long attended to the 

 habits of humble-bees, believes that "more than two-thirds of 

 them are thus destroyed all over England." Now the number of 

 mice is largely dependent, as every one knows, on the number of 

 cats; and Colonel Newman says, "Near villages and small towns 

 I have found the nests of humble-bees more numerous than else- 

 where, which I attribute to the number of cats that destroy the 

 mice." Hence it is quite credible that the presence of a feline 

 animal in large numbers in a district might determine, through the 

 intervention first of mice and then of bees, the frequency of cer- 

 tain flowers in that district! 



In the case of every species, many different checks, acting at 

 different periods of life, and during different seasons or years, 

 probably come into play; some one check or some few being 

 generally the most potent; but all will concur in determining the 

 average number, or even the existence of the species. In some 

 cases it can be shown that widely different checks act on the same 

 species in different districts. When we look at the plants and 

 bushes clothing an entangled bank, we are tempted to attribute 

 their proportional numbers and kinds to what we call chance. 

 But how false a view is this! Every one has heard that when 

 an American forest is cut down, a very different vegetation springs 

 up; but it has been observed that ancient Indian ruins in the 

 Southern United States, which must formerly have been cleared 

 of trees, now display the same beautiful diversity and proportion 

 of kinds as in the surrounding virgin forests. What a struggle 

 must have gone on during long centuries between the several 

 kinds of trees, each annually scattering its seeds by the thousand ; 

 what war between insect and insect — between insects, snails, and 

 other animals, with birds and beasts of prey — all striving to in- 

 crease, all feeding on each other, or on the trees, their seeds and 

 seedlings, or on the other plants which first clothed the ground 

 and thus checked the growth of the trees ! Throw up a handful of 

 feathers, and all fall to the ground according to definite laws; but 

 how simple is the problem where each shall fall, compared to that 



