Origin of Species Variorum

Comparison with 1866

I may add, has also recently shown that the muscles in the larvæ of certain insects are very far from uniform. Authors sometimes argue in a circle when they state that important organs never vary; for these same authors practically rank that character as important (as some few naturalists have honestly confessed) which does not vary; and, under this point of view, no instance will ever be found of an important part varying: but under any other point of view many instances assuredly can be given.

There is one point connected with individual differences, which seems to me extremely perplexing: I refer to those genera which have sometimes been called "protean" or "polymorphic," in which the species present an inordinate amount of variation; and hardly two naturalists can agree which forms to rank as species and which as varieties. ↑ We may instance Rubus, Rosa, and Hieracium amongst plants, several genera of insects, several genera of Brachiopod shells, and the Ruff (Machetes pugnax) amongst birds. In most polymorphic genera some of the species have fixed and definite characters. Genera which are polymorphic in one country seem to be, with some few exceptions, polymorphic in other countries, and likewise, judging from Brachiopod shells, at former periods of time. These facts seem to be very perplexing, for they seem to show that this kind of variability is independent of the conditions of life. I am inclined to suspect that we see in these polymorphic genera variations in points of structure which are of no service or disservice to the species, and which consequently have not been seized on and rendered definite by natural selection, as hereafter will be explained.

Individuals of the same species often present great differences of structure, not directly connected with variability, as in the two sexes, as in the two or three castes of sterile females or workers amongst insects, and as in the immature and larval states of all animals. There are, however, other cases, namely of dimorphism and trimorphism, which might easily be, and have frequently been, confounded with variability, but which are really quite distinct. I refer to the two or three distinct forms, which certain animals of either sex, and certain hermaphrodite plants, habitually present. Thus, Mr. Wallace, who has lately called special attention to the subject, has shown that the females of certain species of butterflies, in the Malayan archipelago, regularly appear under two or even three conspicuously distinct forms, not connected together by intermediate varieties. The winged and frequently wingless states of so many Hemipterous insects may probably be included as a case of dimorphism, and not of mere variability. Fritz Müller, also, has recently described analogous but more extraordinary cases in the males of certain Brazilian Crustaceans: thus, the male of a Tanais regularly occurs under two widely different forms, not connected by any intermediate links; one of these forms has much stronger and differently shaped pincers for seizing the female, and the other, as if for compensation, has antennæ much more abundantly furnished with smelling-hairs, so as to have a better chance of finding the female. ↑ Again, the males of another Crustacean, an Orchestia, occur under two distinct forms, with pincers differing much more from each other in structure, than do the pincers of most species of the same genus. With respect to plants I have recently shown that species in several widely distinct orders present two or even three forms, which are abruptly distinguished from each other in several important points, as in the size and colour of the pollen-grains; and these forms, though all hermaphrodites, differ from each other in their reproductive power, so that for full fertility, or indeed in some cases for any fertility, they must reciprocally impregnate each other. Although the forms of the few dimorphic and trimorphic animals and plants which have been studied are not now connected together by intermediate links, it is probable that this will be found to occur in other cases; for Mr. Wallace observed a certain butterfly which presented in the same island a great range of varieties connected by intermediate links, and the extreme links of the chain closely resembled the two forms of an allied dimorphic species inhabiting another part of the Malay archipelago. Thus also with ants, the several worker-castes are generally quite distinct; but in some cases, as we shall hereafter see, the castes are connected together by graduated varieties. It certainly at first appears a highly remarkable fact that the same female butterfly should have the power of producing at the same time three distinct female forms and a male; that a male Crustacean should generate two male forms and a female form, all widely different from each other; and that an hermaphrodite plant should produce from the same seed-capsule three distinct hermaphrodite forms, bearing three different kinds of females and three or even six different kinds of males. Nevertheless these cases are only exaggerations of the universal fact that every female animal produces males and females, which in some instances differ in so wonderful a manner from each other.

Doubtful Species.

The forms which possess in some considerable degree the character of species, but which are so closely similar to .. other forms, or are so closely linked to them by intermediate gradations, that naturalists do not

I may add, has also quite recently shown that the muscles in the larvæ of certain insects are very far from uniform. Authors sometimes argue in a circle when they state that important organs never vary; for these same authors practically rank that character as important (as some few naturalists have honestly confessed) which does not vary; and, under this point of view, no instance of an important part varying will ever be found: but under any other point of view many instances assuredly can be given.

There is one point connected with individual differences, which is extremely perplexing: I refer to those genera which have sometimes been called "protean" or "polymorphic," in which the species present an inordinate amount of variation; and hardly two naturalists can agree which forms to rank as species and which as varieties. ↑ We may instance Rubus, Rosa, and Hieracium amongst plants, several genera of insects, and several genera of Brachiopod shells. In most polymorphic genera some of the species have fixed and definite characters. Genera which are polymorphic in one country seem to be, with some few exceptions, polymorphic in other countries, and likewise, judging from Brachiopod shells, at former periods of time. These facts are very perplexing, for they seem to show that this kind of variability is independent of the conditions of life. I am inclined to suspect that we see in these polymorphic genera variations in points of structure which are of no service or disservice to the species, and which consequently have not been seized on and rendered definite by natural selection, as hereafter will be explained. ↑

Those forms which possess in some considerable degree the character of species, but which are so closely similar to some other forms, or are so closely linked to them by intermediate gradations, that naturalists do not