Wollaston, lie much concealed, until the wind lulls and the sun shines;
that the proportion of wingless beetles is larger on the exposed Desertas
than in Madeira itself; and especially the extraordinary fact, so strongly
insisted on by Mr. Wollaston, that certain large groups of beetles,
elsewhere excessively numerous, which absolutely require the use of their
wings, are here almost entirely absent. These several considerations make
me believe that the wingless condition of so many Madeira beetles is mainly
due to the action of natural selection, combined probably with disuse. For
during many successive generations each individual 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
destroyed.
The insects in Madeira which are not ground-feeders, and which, as certain
flower-feeding coleoptera and lepidoptera, must habitually use their wings
to gain their subsistence, have, as Mr. Wollaston suspects, their wings not
at all reduced, but even enlarged. This is quite compatible 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 individuals were saved
by successfully battling with the winds, or by giving up the attempt and
rarely or never flying.
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