Essays on Life 



of a hair, as they do when we bring forward 

 what we deem excellent instances of the 

 transmission of an acquired characteristic, 

 why may not we, too, demand at any rate 

 some evidence that the unmodified beetles 

 actually did always, or nearly always, get 

 blown out to sea, during the reduction above 

 referred to, and that it is to this fact, and not 

 to the masterly inactivity of their fathers and 

 mothers, that the Madeira beetles owe their 

 winglessness ? If we began stickling for proof 

 in this way, our opponents would not be long 

 in letting us know that absolute proof is un- 

 attainable on any subject, that reasonable 

 presumption is our highest certainty, and that 

 crying out for too much evidence is as bad as 

 accepting too little. Truth is like a photo- 

 graphic sensitised plate, which is equally ruined 

 by over and by under exposure, and the just 

 exposure for which can never be absolutely 

 determined. 



Surely if disuse can be credited with the 

 vast powers involved in Mr. Darwin's state- 

 ment that it has probably "been the main 



agent in rendering organs rudimentary," no 



270 



