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Show 140 LAWS OF VARIATION. (CHAP. V. only a specific character, and ~o ~ne would be surprise~ at one of the blue species varying Into red, or conversely' but if all the species had blue :fl.owers,, th.e colour would bec01ne a generic character, and Its vanatlon ~ould be a more unusual circumstance. I have c~osen .this ex.ample because an explanation is not in this case apphcable, which most naturalists would advance, namely.' that specific characters are 1nore variable th.an g.ene~IC, because they are taken frorn parts of less physiologicalimport~nce than those commonly used for classing .ge~era. I beheve this explanation is partly, yet only Induectly, true; I shall, however, have to return to this subject in our chapter on Classification. It would be almost superfluous to adduce evidence in support of the above state~ent, that specific characters are more variable than gen~ric ; but I have repeatedly noticed in works on natural h1story, that when an author has rmnarked with surprise that some important organ or part, which i~ generall1 very con~tant throughout large groups of spemes~ has differed considm:ably in closely-allied species, that It has, a;lso, been var~able in the individuals of some of the spemes. And th1s fact shows that a character, which is generally of generic value ·w·hen it sinks in value and becomes only of specific value' often beconws variable, though its physiological impoi:tance may remain the same. Something of the same kind applies to ~onstrosities : at least Is. Geoffroy St. I-Iilaire seems to entertain no doubt, that the more an organ normally differs in the different species of the same group the more subject it is to individual anomalies. 0~ the ordinary view of each species having been independently created, why should that part of the structure, which differs from the same part in other independently- created species of the same genus, be more variable than those parts which are closely alike in the several species? I do not see that any explanation can be given. But on the view of species being only strongly marked and fixed varieties, we might surely expect to find them stUl often continuing to vary in those parts of their structure which have varied within a moderately recent period, and which have thus come to differ. Or to state the case CHAP. V.] LAWS OF- VARIATION. 141 in another manner :-the points in which all tne species of a genus res.emble each other, and in which they differ from the species of some other genus, are called generic characters; and these characters in common I attribute to inheritance from a comrnon progenitor, for it can rarely have happened that nat~ral selection will have modified several species, fitted to more or less widely-different habits, in exactly the same manner: and as these so-called generic characters have been inherited from a remote period, since that period when the species first branched off from their common progenitor, and subsequently have not varied or come to differ in any degree, or only in a slight degree, it_is not probable that they should vary at the present day. On the other hand, the points in which species differ from other species of the same genus, are called specific characters; and as· these specific characters have varied and come to differ withi~ the period of the branching off of the species from a common progenitor, it is probable that they should still often be in some degree variable,-at least more variable than those parts of the organisation which have for a very long period remained constant. In connexion 'vith the present subject, I will make only two other remarks. I think it will be admitted, without my entering on details, that secondary sexual characters are very variable; I think it also will be admitted that species of the same group differ from each other more widely in their secondary sexual characters, than in other parts of their organisation ; compare, for instance, the amount of di.fferenc~ between the males of gallinaceous birds, in which secondary sexual characters are strongly displayed, with the amount of difference bet~ een their females ; and the truth of this proposition Will be granted. The cause of the original variability of secondary sexual characters is not manifest ; but we can see why these characters should not have been rendered as constant and uniform as other parts of the organisation ; for secondary sexual characters have been accumulated by ~exual selec~ion, w~ich is less ·rigid in its action than ord1nary selection, as It does not entail death, but only |