| → of the almost entire absence of 1859 1860 1861 1866 1869 |
| that 1872 |
|
| → groups have habits of life almost necessitating frequent flight;— 1859 1860 1861 |
| groups have habits of life almost necessitating frequent flight; — 1866 1869 |
| absolutely require the use of their wings, are here almost entirely absent;— 1872 |
|
|
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 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. 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.
|
