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Show 140 DARWINIRM CHAP. that they are inherited, and that t~cy a1·e constant. AdmittinO' that this peculiar appendage IS (as Mr. Romanes ayfl rather 0 confidently, "we happen to know it to be") wholly useless and meaningless, the fact would be rather an argument against specific characters being ~ls? mean~ngless,. becaus~ the latter never have the charactenstics which this particular variation possesses. These useless or non-adaptive characters are, apparently, of the same nature as the "sports" that arise in our domestic productions, but which, as. Mr. Darwin . says, without the ai<l of selection would soon disappear; while some of them may be correlations with other characters which are or have been useful. Some of these correlations arc very curious. Mr. Tcgctmcier informed Mr. Darwin that the young of white, yellow, or dun-coloured pigeons are born almo t naked, whereas other coloured pigeons arc born well clothed with down. Now, if this difference occurred between wild ~pccies of different colonri'\, it might be said that the nakedness of the young could not lw of any use. But the colour with which it is correlated might., as has been shown, be useful in many ways. The sl<jn and its various appendages, as horns, hoofs, hair, feathers, ~md teeth, arc homologous parts, and are subject to very strange correlations of growth. In Paraguay, horses with curled hair occnr, and these always have hoofs exactly like those of a mnlc, while the hair of the mane and tail is much shorter tba,n u ual. Now, if any one of these characters were useful, tho others correlated with it might be themselves useless, but would still be tolerably constant because dependent on a useful organ. So the tusks and the bristles of tho boar arc correlated and vary in development together, and the fm'mcr only may he useful, or both may be useful in unequal degrees. Tho difficulty as to how individual differences or sports can become fixed and perpetuated, if altogether useless, is cvacl <l by those who bold that such characters arc exceedingly common. Mr. Romancs says that, upon his theory of physiological selection, "it is quite intelligible that when a varietal form is differentiated from its parent form by the bar of sterility, any little meaningless peculiarities of structure or of instinct should at first be allowed to arise, and that they should then be allouwl to perpetuate themselves by heredity," until they are finally Vl DIFFICULTIES AND OBJECTIONS 141 e~iminated by d!suse. But ~hi~ . is entirely begging the questiOn. Do meamngless pccuhantles, which we aclmit often arise as spontaneous variations, ever perpetuate themselves in aU the individuals constituting a variety or race, without selection either human or natural 1 Such characters present themselves as unstable variations, and as such they remain, unless preserved and accumulated by selection; and they can therefore never b~come "specific" cha~acters unless they arc strictly correlated With some useful and Important peculiarities. As bearing upon this question we may refer to what is termed Delbceu~'s la,':, which has been thus briefly stated by Mr. Murphy m h1s work on lfabit and Jntelliaence 1). 241. ;; ' ."If, i~ an1 species, a number_ of individuals, bearing :t ratiO not mfimtely small to the cnt1rc number of births, are in every generation born with a particular variation which is neithe7 beneficial nor injur~ous, and if it is not counteracted by reversiOn, then the proportiOn of the new variety to the ori<Yinal form will increase till it approaches indefinitely nea~ to equality." It is not impossible that some definite varieties, such as the melanic form of the jaguar and the bridled variety of the o·uill cmot are due to this cause ; but from their very naturc 0 • uch varieties are unstable, and are continually reproduced in varying proportions from the pn.rent forms. They can, therefore, never constitute species unless the variation in question becomes beneficial, when it will be fixed by natnml selection. Darwin, it is true, says-" There can be littl0 doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aiel of any form of selection." 1 But no proof whatever is offered of thi. statement, and it is so entirely opposed to all we know of the facts of variation as given by Darwin himself, th<tt the important word "all" is probably an oversight. On the whole, then, I submit, not only bas it not been proved that an " enormous number of specific peculiarities " are useless, and that, as a logical result, nn,tural selection is "not a theory of the origin of species," but only of the origin 1 Origin of Species, p. 72. |