Finally, as rudimentary organs, by whatever steps they may have been
degraded into their present useless condition, are the record of a former
state of things, and have been retained solely through the power of
inheritance--we can understand, on the genealogical view of classification,
how it is that systematists, in placing organisms in their proper places in
the natural system, have often found rudimentary parts as useful as, or
even sometimes more useful than, parts of high physiological importance.
Rudimentary organs may be compared with the letters in a word, still
retained in the spelling, but become useless in the pronunciation, but
which serve as a clue for its derivation. On the view of descent with
modification, we may conclude that the existence of organs in a
rudimentary, imperfect, and useless condition, or quite aborted, far from
presenting a strange difficulty, as they assuredly do on the old doctrine
of creation, might even have been anticipated in accordance with the views
here explained.
SUMMARY.
In this chapter I have attempted to show that the arrangement of all
organic beings throughout all time in groups under groups--that the nature
of the relationships by which all living and extinct organisms are united
by complex, radiating, and circuitous lines of affinities into a few grand
classes--the rules followed and the difficulties encountered by naturalists
in their classifications--the value set upon characters, if constant and
prevalent, whether of high or of the most trifling importance, or, as with
rudimentary organs of no importance--the wide opposition in value between
analogical or adaptive characters, and characters of true affinity; and
other such rules--all naturally follow if we admit the common parentage of
allied forms, together with their modification through variation and
natural selection, with the contingencies of extinction and divergence of
character.
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