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Show 484 CONCLUSION. CHAP. XIV. embraces aI I the me mbers of the same class. I 1b eli£e ve that an.i ma1s h ave descended from at most on y our or fi ve progeni' to rs, and plants from an equal or lesser number. h 1 Analogy would lead me one step furt er, name y, to the belief that all animals and plants have descended f rom some on e Prototype · But analogy. may be a de- 'tf 1 'de Nevertheless all living th1ngs have much Cei u gu1 . . . h . · I· n commo· n, 1·n the1'r chemical compositio.n , t eir germina1 vesi·C 1e s, their cellular structure, and th.e ir law'sf lo' f grow·t h and reproduction. We see this even 1n s? t:r Ing a Cir-cumstance as that the same poison o~ten similarly affects plants and animals ; or that the po1son secre~ed by the gall-fly produces monstrous growths on the wild rose or oak-tree. Therefore I should infer from analogy ~hat . b bly all the organic beings which have ever hved p1o a · a· 1 on this earth have descended from some one pnmor Ia \ form, into which life was first breathed. When the views entertained in this volume on the origin of species, or when analogous views a:e generally admitted, we can dimly foresee that there will be a c?nsiderable revolution in natural history. Systematists will be able to pursue their labours as at present ; but they will not be incessantly haunted by the shado_wy doubt whether this or that form be in ess~nce a sp.emes. This I feel sure, and I speak after exponence, will be no slight relief. The endless disputes whether or ~ot some fifty species of British brambles are true. species will cease. Systematists will have only to docid~ (not that this will be easy) whether any form be suffimently constant and distinct from other forms, to b~ capable of definition ; and if definable, whether the ~Ifferen~:s be sufficiently important to deserve a specrfic. na . This latter point will become a far more essentral con- CHAP. XIV. CONCLUSION. 485 sideration than it is at present ; for differences, however slight, between any two forms, if not blended by intermediate gradations, are looked at by most naturalists as sufficient to raise both forms to the rank of species. Hereafter we shall be compelled to acknowledge that the only distinction between species and well-marked varieties is, that the latter are known, or believed, to be connected at the present day by intermediate gradations, whereas species were formerly thus connected. Hence, without quite rejecting the consideration of the present existence of intermediate gradations between any two forms, we shall be led to weigh more carefully and to value higher the actual amount of difference between them. It is quite possible that forms now generally acknowledged to be n1erely varie .. ties may hereafter be thought worthy of specific names, as with the primrose and cowslip ; and in this case scientific and common language will come into accordance. In short, we shall have to treat species in the same manner as those naturalists treat genera, who admit that genera are merely artificial combinations made for convenience. This may not be a cheering prospect; but we shall at least be freed from the vain search for the undiscovered and undiscoverable essence of the term species. The other and more general departments of natural history will rise greatly in interest. The terms used by naturalists of affinity, relationship, community of type, paternity, morphology, adaptive characters, rudimentary and aborted organs, &c., will cease to be metaphorical, and will have a plain signification. When we no longer look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure |
