136 LAWS OF VAKIATION. Chap. V. 



cealed, until the wind lulls and the sun shines; that 

 the proportion of wingless beetles is larger on the ex- 

 posed Dezertas than in Madeira itself; and especially 

 the extraordinary fact, so strongly insisted on by Mr. 

 Wollaston, of the almost entire absence of certain large 

 groups of beetles, elsewhere excessively numerous, and 

 which groups have habits of life almost necessitating 

 frequent flight ; — these several considerations have made 

 me believe that the wingless condition of so many 

 Madeira beetles is mainly due to the action of natural 

 selection, but combined probably with disuse. For 

 during thousands of successive generations each indi- 

 vidual beetle which flew least, either from its wings 

 having been ever so little less perfectly developed or 

 from indolent habit, will have had the best chance of 

 surviving from not being blown out to sea ; and, on the 

 other hand, those beetles which most readily took to 

 flight will oftenest have been blown to sea and thus 

 have been destroyed. 



The insects in Madeira which are not ground-feeders, 

 and which, as the flower-feeding coleoptera and lepidop- 

 tera, must habitually use their wings to gain their subsist- 

 ence, have, as Mr. Wollaston suspects, their wings not 

 at all reduced, but even enlarged. This is quite com- 

 patible with the action of natural selection. For when 

 a new insect first arrived on the island, the tendency 

 of natural selection to enlarge or to reduce the wings, 

 would depend on whether a greater number of indivi- 

 duals were saved by successfully battling with the winds, 

 or by giving up the attempt and rarely or never flying. 

 As with mariners shipwrecked near a coast, it would 

 have been better for the good swimmers if they had 

 been able to swim still further, whereas it would have 

 been better for the bad swimmers if they had not been 

 able to swim at all and had stuck to the wreck. 



