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due to natural selection. Mr. Wollaston has discovered the remarkable fact that 200
out of the 550 species
→(but more are now known) which inhabit
are so far deficient in wings that they cannot fly; and
of the twenty-nine endemic genera, no less than twenty-three
have all their species in this condition! Several
that beetles in many parts of the world are
frequently blown to sea and perish; that the beetles in Madeira, as observed by Mr. Wollaston, lie much
until the wind lulls and the sun shines; that the proportion of wingless beetles is larger on the exposed
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,
which
→groups have habits of life almost necessitating frequent flight; —
these several considerations
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
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
oftenest have been blown to
and thus
destroyed. |
| The insects in Madeira which are not ground-feeders, and which, as
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
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