86 ON THE ORIGIN OF SPECIES 



by the mouth. Bearing such facts in mind, I can see 

 no reason to doubt that an accidental deviation in the 

 size and form of the body, or in the curvature and 

 length of the proboscis, etc., far too slight to be 

 appreciated by us, might profit a bee or other insect, 

 so that an individual so characterised would be able to 

 obtain its food more quickly, and so have a better 

 chance of living and leaving descendants. Its descend- 

 ants would probably inherit a tendency to a similar 

 slight deviation of structure. The tubes of the corollas 

 of the common red and incarnate clovers (Trifolium 

 pratense and incarnatum) do not on a hasty glance 

 appear to differ in length ; yet the hive-bee can easily 

 suck the nectar out of the incarnate clover, but not 

 out of the common red clover, which is visited by 

 humble-bees alone ; so that whole fields of the red 

 clover offer in vain an abundant supply of precious 

 nectar to the hive-bee. Thus it might be a great 

 advantage to the hive-bee to have a slightly longer or 

 differently constructed proboscis. On the other hand, 

 I have found by experiment that the fertility of clover 

 depends on bees visiting and moving parts of the 

 corolla, so as to push the pollen on to the stigmatic 

 surface. Hence, again, if humble-bees were to become 

 rare in any country, it might be a great advantage to 

 the red clover to have a shorter or more deeply divided 

 tube to its corolla, so that the hive-bee could visit its 

 flowers. Thus I can understand how a flower and a 

 bee might slowly become, either simultaneously or one 

 after the other, modified and adapted in the most 

 perfect manner to each other, by the continued pre- 

 servation of individuals presenting mutual and slightly 

 favourable deviations of structure. 



I am well aware that this doctrine of natural selec- 

 tion, exemplified in the above imaginary instances, is 

 open to the same objections which were at first urged 

 against Sir Charles Ly ell's noble views on ( the modern 

 changes of the earth, as illustrative of geology ' ; but 

 we now seldom hear the action, for instance, of the 

 coast-waves, called a trifling and insignificant cause. 





