Dysteleology, or the theory of purposelessness [is] the name I have given to the science of rudimentary organs, of suppressed and degenerated, aimless and inactive, parts of the body; one of the most important and most interesting branches of comparative anatomy, which, when rightly estimated, is alone sufficient to refute the fundamental error of the teleological and dualistic conception of Nature, and to serve as the foundation of the mechanical and monistic conception of the universe.
It will be sufficient to quote Professor Huxley's remarks upon this passage, taken from the very laudatory review he wrote of the work in which it occurs.[225][{191}]
Professor Haeckel has invented a new and convenient name, "Dysteleology," for the study of the "purposelessnesses" which are observable in living organisms—such as the multitudinous cases of rudimentary and apparently useless structures. I confess, however, that it has often appeared to me that the facts of Dysteleology cut two ways. If we are to assume, as evolutionists in general do, that useless organs atrophy, such cases as the existence of lateral rudiments of toes in the foot of a horse place us in a dilemma. For, either these rudiments are of no use to the animal, in which case, considering that the horse has existed in its present form since the Pliocene epoch, they surely ought to have disappeared; or they are of some use to the animal, in which case they are of no use as arguments against Teleology. A similar, but stronger argument may be based upon the existence of teats, and even functional mammary glands in male mammals.... There can be little doubt that the mammary gland was as apparently useless in the remotest male mammalian ancestor of man as in living men, and yet it has not disappeared. Is it then still profitable to the male organism to retain it? Possibly; but in that case its dysteleological value is gone.
In later editions Professor Huxley further observed: "The recent discovery of the important part played by the Thyroid gland should be a warning to all speculators about useless organs."[226][{192}]
It seems, therefore, the wiser part to refrain from basing any vital conclusions upon these organs until we can assure ourselves that our knowledge warrants our so doing. As the same Professor Huxley intimated, it might be well for palæontologists, and doubtless for biologists likewise,[227] "To learn a little more carefully that scientific 'ars artium,' the art of saying 'I don't know.'"
So again as to the phenomena of embryology. No doubt they are very striking and impressive. That the most highly developed creatures, and man himself, should in the first stages of existence exhibit the characteristics of lower forms, is an exemplification of development no less signal than the succession of ascending types witnessed to by the rocks. It is not easy to see, however, why it should be taken for granted that this can only signify genetic descent from all such forms, and that these embryo animals are engaged in climbing up their genealogical trees. Yet this is usually assumed as a matter of course, and any one who ventures to question the validity of such an inference, must be prepared to find himself accused of dogmatizing.
And yet, after all, upon what grounds does the assumption rest? That such a recapitulation of racial experiences forms no essential feature of Evolution is sufficiently evident from the case of the vegetable world,—for plants do not climb their[{193}] genealogical trees, or pass in the seed through a series of botanical phases. And as to animals, since through all varieties of form, each always arrives at the required term, it is obvious that, apart from any archaic associations, and on Darwinian principles themselves, these forms must be the best for the purpose at each respective stage,—perhaps the only ones by which the term could be reached. It is therefore, to say the least, quite conceivable, that we have here the whole explanation and need go no further.
In certain instances this obvious consideration is strikingly illustrated. Thus the salamander, an Amphibian of the newt family, brings forth its young in adult condition without gills.[228] But previously to birth they have gills relatively large. The experiment having been tried of bringing some of them forth by artificial means before their time, and placing them in water, the first thing they did was to cast off these big gills, which were speedily replaced by new ones of much smaller size, and evidently better suited for the work required, as they lasted as long as a fortnight.
Here, in the first place, it is quite impossible to suppose that the large gills would continue to appear unless they were of advantage during the period of gestation. It is equally evident that it is not from a previous aquatic condition that they are inherited, for in such a condition they are useless. Finally, as Mr. Mivart observes, the new gills, suitable[{194}] for unwonted conditions, were developed "not in a struggle for existence against rivals, but directly and spontaneously from the innate nature of the animal."
This view of the matter commended itself on mature consideration to so ardent an evolutionist as Carl Vogt, with whom we may couple M. de Quatrefages, who cites his words with approval as follows:[229]