"In some cases we might easily put down to disuse modifications of
structure, which are wholly or mainly due to natural selection. Mr.
Wollaston has discovered the remarkable fact that 200 beetles, out of the
550 species (but more are now known) inhabiting Madeira, are so far
deficient in wings that they cannot fly; and that of the 29 endemic
genera no less than 23 have all their species in this condition! Several
facts,--namely, that beetles in many parts of the world are frequently
blown out to sea and perish; that the beetles in Madeira, as observed by
Mr. 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_ [italics mine]. 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." {27}
We should like to know, first, somewhere about how much disuse was able
to do after all, and moreover why, if it can do anything at all, it
should not be able to do all. Mr. Darwin says: "Any change in structure
and function which can be effected by small stages is within the power of
natural selection." "And why not," we ask, "within the power of use and
disuse?" Moreover, on a later page we find Mr. Darwin saying:--
"_It appears probable that disuse has been the main agent in rendering
organs rudimentary_ [italics mine]. It would at first lead by slow steps
to the more and more complete reduction of a part, until at last it has
become rudimentary--as in the case of the eyes of animals inhabiting dark
caverns, and of the wings of birds inhabiting oceanic islands, which have
seldom been forced by beasts of prey to take flight, and have ultimately
lost the power of flying. Again, an organ, useful under certain
conditions, might become injurious under others, _as with the wings of
beetles living on small and exposed islands_; and in this case natural
selection will have aided in reducing the organ, until it was rendered
harmless and rudimentary [italics mine]." {28}
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Elsewhere in the archive
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account