Science in Arcady | Page 7

species had left behind it in its native
European or African mainland.
I said a little while ago we had no mammal in the islands. In that I was
not quite strictly correct. I ought to have said, no terrestrial mammal. A
little Spanish bat got blown to us once by a rough nor'easter, and took
up its abode at once among the caves of our archipelago, where it
hawks to this day after our flies and beetles. This seemed to me to show
very conspicuously the advantage which winged animals have in the
matter of cosmopolitan dispersion; for while it was quite impossible for
rats, mice, or squirrels to cross the intervening belt of three hundred

leagues of sea, their little winged relation, the flitter-mouse, made the
journey across quite safely on his own leathery vans, and with no
greater difficulty than a swallow or a wood-pigeon.
The insects of my archipelago tell very much the same story as the
birds and the plants. Here, too, winged species have stood at a great
advantage. To be sure, the earliest butterflies and bees that arrived in
the fern-clad period were starved for want of honey; but as soon as the
valleys began to be thickly tangled with composites, harebells, and
sweet-scented myrtle bushes, these nectar-eating insects established
themselves successfully, and kept their breed true by occasional crosses
with fresh arrivals blown to sea afterwards. The development of the
beetles I watched with far greater interest, as they assumed fresh forms
much more rapidly under their new conditions of restricted food and
limited enemies. Many kinds I observed which came originally from
Europe, sometimes in the larval state, sometimes in the egg, and
sometimes flying as full-grown insects before the blast of the angry
tempest. Several of these changed their features rapidly after their
arrival in the islands, producing at first divergent varieties, and finally,
by dint of selection, acting in various ways, through climate, food, or
enemies, on these nascent forms, evolving into stable and well-adapted
species. But I noticed three cases where bits of driftwood thrown up
from South America on the western coasts contained the eggs or larvae
of American beetles, while several others were driven ashore from the
Canaries or Madeira; and in one instance even a small insect, belonging
to a type now confined to Madagascar, found its way safely by sea to
this remote spot, where, being a female with eggs, it succeeded in
establishing a flourishing colony. I believe, however, that at the time of
its arrival it still existed on the African continent, but becoming extinct
there under stress of competition with higher forms, it now survives
only in these two widely separated insular areas.
It was an endless amusement to me during those long centuries, while I
devoted myself entirely to the task of watching my fauna and flora
develop itself, to look out from day to day for any chance arrival by
wind or waves, and to follow the course of its subsequent vicissitudes
and evolution. In a great many cases, especially at first, the new-comer

found no niche ready for it in the established order of things on the
islands, and was fain at last, after a hard struggle, to retire for ever from
the unequal contest. But often enough, too, he made a gallant fight for
it, and, adapting himself rapidly to his new environment, changed his
form and habits with surprising facility. For natural selection, I found,
is a hard schoolmaster. If you happen to fit your place in the world, you
live and thrive, but if you don't happen to fit it, to the wall with you
without quarter. Thus sometimes I would see a small canary beetle
quickly take to new food and new modes of life on my islands under
my very eyes, so that in a century or so I judged him myself worthy of
the distinction of a separate species; while in another case, I remember,
a south European weevil evolved before long into something so wholly
different from his former self that a systematic entomologist would
have been forced to enrol him in a distinct genus. I often wish now that
I had kept a regular collection of all the intermediate forms, to present
as an illustrative series to one of your human museums; but in those
days, of course, we none of us imagined anybody but ourselves would
ever take an interest in these problems of the development of life, and
we let the chance slide till it was too late to recover it.
Naturally, during all these ages changes of other sorts were going on in
my islands--elevations and subsidences, separations and reunions,
which helped to modify the life of the group considerably. Indeed,
volcanic action was constantly at work altering the