The Foundations of the Origin of Species Two Essays written in 1842 and 1844 · Charles Darwin
ABORTIVE OR RUDIMENTARY ORGANS
_The abortive organs of naturalists._ Parts of structure are said to be "abortive," or when in a still lower state of development "rudimentary{486}," when the same reasoning power, which convinces us that in some cases similar parts are beautifully adapted to certain ends, declares that in others they are absolutely useless. Thus the rhinoceros, the whale{487}, etc., have, when young, small but properly formed teeth, which never protrude from the jaws; certain bones, and even the entire extremities are represented by mere little cylinders or points of bone, often soldered to other bones: many beetles have exceedingly minute but regularly formed wings lying under their wing-cases{488}, which latter are united never to be opened: many plants have, instead of stamens, mere filaments or little knobs; petals are reduced to scales, and whole flowers to buds, which (as in the feather hyacinth) never expand. Similar instances are almost innumerable, and are justly considered wonderful: probably not one organic being exists in which some part does not bear the stamp of inutility; for what can be clearer{489}, as far as our reasoning powers can reach, than that teeth are for eating, extremities for locomotion, wings for flight, stamens and the entire flower for reproduction; yet for these clear ends the parts in question are manifestly unfit.
Abortive organs are often said to be mere representatives (a metaphorical expression) of similar parts in other organic beings; but in some cases they are more than representatives, for they seem to be the actual organ not fully grown or developed; thus the existence of mammae in the male vertebrata is one of the oftenest adduced cases of abortion; but we know that these organs in man (and in the bull) have performed their proper function and secreted milk: the cow has normally four mammae and two abortive ones, but these latter in some instances are largely developed and even (??) give milk{490}. Again in flowers, the representatives of stamens and pistils can be traced to be really these parts not developed; Koelreuter has shown by crossing a diaecious plant (a Cucubalus) having a rudimentary pistil{491} with another species having this organ perfect, that in the hybrid offspring the rudimentary part is more developed, though still remaining abortive; now this shows how intimately related in nature the mere rudiment and the fully developed pistil must be. {486} In the _Origin_, Ed. i. p. 450, vi. p. 619, the author does not lay stress on any distinction in meaning between the terms _abortive_ and _rudimentary_ organs. {487} _Origin_, Ed. i. p. 450, vi. p. 619. {488} _Ibid._ {489} This argument occurs in _Origin_, Ed. i. p. 451, vi. p. 619.
These two classes of facts, however, blend into each other{497}; by parts accidentally aborted, during the embryonic life of one individual, becoming hereditary in the succeeding generations: thus a cat or dog, born with a stump instead of a tail, tends to transmit stumps to their offspring; and so it is with stumps representing the extremities; and so again with flowers, with defective and rudimentary parts, which are annually produced in new flower-buds and even in successive seedlings. The strong hereditary tendency to reproduce every either congenital or slowly acquired structure, whether useful or injurious to the individual, has been shown in the first part; so that we need feel no surprise at these truly abortive parts becoming hereditary. A curious instance of the force of hereditariness is sometimes seen in two little loose hanging horns, quite useless as far as the function of a horn is concerned, which are produced in hornless races of our domestic cattle{498}. Now I believe no real distinction can be drawn between a stump representing a tail or a horn or the extremities; or a short shrivelled stamen without any pollen; or a dimple in a petal representing a nectary, when such rudiments are regularly reproduced in a race or family, and the true abortive organs of naturalists.
And if we had reason to believe (which I think we have not) that all abortive organs had been at some period _suddenly_ produced during the embryonic life of an individual, and afterwards become inherited, we should at once have a simple explanation of the origin of abortive and rudimentary organs{499}. In the same manner as during changes of pronunciation certain letters in a word may become useless{500} in pronouncing it, but yet may aid us in searching for its derivation, so we can see that rudimentary organs, no longer useful to the individual, may be of high importance in ascertaining its descent, that is, its true classification in the natural system. {496} _Origin_, Ed. i. p. 454, vi. p. 625. {497} In the _Origin_, Ed. i. p. 454, vi. p. 625, the author in referring to semi-monstrous variations adds "But I doubt whether any of these cases throw light on the origin of rudimentary organs in a state of nature." In 1844 he was clearly more inclined to an opposite opinion. {498} _Origin_, Ed. i. p. 454, vi. p. 625. {499} See _Origin_, Ed. i. p. 454, vi. p. 625. The author there discusses monstrosities in relation to rudimentary organs, and comes to the conclusion that disuse is of more importance, giving as a reason his doubt "whether species under nature ever undergo abrupt changes." It seems to me that in the _Origin_ he gives more weight to the "Lamarckian factor" than he did in 1844. Huxley took the opposite view, see the Introduction.
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