136 
LAWS OF VARIATION. 
Chap. V. 
until the wind lulls and tlie sun shines ; that the pro¬ 
portion of wingless beetles is larger on the exposed 
Desertas than in Madeira itself; and especially the 
extraordinary fact, so strongly insisted on by Mr. Wol¬ 
laston, 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. JFor 
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 would 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. 
