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Show 4:18 CONCLUSION [CIIA.P. XIV. thought were speci~l ?reations, and. which are .still thus looked at by the maJOrity of naturahsts, and whiCh conse~ quently have every external characteristic feature of true species,-they admit that these have been p~·oduced by variation but they refuse to extend the same view to other and very' slightly different forms. N evert~eless they . do not pretend that they can define, or eve~ conJecture, whiCh are the created forms of life, and whi~h are. t~ose produced by secondary laws. The:y ad.rrnt ':anat;o~ as a vera causa in one case, they arbitranly reJect It In another without assiO'ning any distinction in the two cases. Tbe day will com~ wh.en this will be given. as a c~r~ous illustration of the bhndness of preconcm ved opinion. These authors seem no more startled at a miraculous act of creation than at an ordinary birth. But do they really believe that at innumerable periods in the earth's history certain elemental atoms have been commanded suddenly to flash into living tissues ? Do they believe that at each supposed act of creation one individual or many were produced ? Were all the infinitely numerous kinds of animals and plants created as eggs or seed, or as full grown? and in the case of mammals, were they created bearing the false marks of nourishment from the mother's womb? Although naturalists very properly demand a full explanat~o~ of every. difficulty ~rom th~se who ~elieve in the mutabihty of species, on their own side they Ignore the whole subject of the first appearance of species in what they consider reverent silence. It may be asked how far I extend the doctrine of the modification of species. The question is difficult to answer because the more distinct the forms are which we may' consider, by so much the arguments fall away in force. But some arguments of the greatest weight extend very far. All the members of whole classes can be connected together by chai;ns . of a~nities, and all . can be classified on the same principle, m groups subordinate to groups. Fossil remains sometimes tend to :fill ~p very wide intervals between existing orders. Organs In a .rudimentary condition plainly show that an early ~r~genitor had the organ in a fully developed state; and this m some e'HA.P. XIV.l CONCLUSION. 419 instances necessarily implies an enormous amount of modification in the descendants. Throughout whole classes various structures are formed on the same pattern, and at an entbryonic age the species closely resemh1e each other. Therefore I cannot doubt that the theory of descent with modification embraces all the members of the same class. I believe that animals have descended frorn at most only four or five progenitors, and plants from an equal or lesser number. · Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide. Nevertheless all living things have much in common, in their chemical composition, their germinal vesicles, their cellular structure, and their laws of growth andreproduction. We see this even in so trifling a circumstance as that the same poison often similarly affects plants and animals; or that the poison secreted by the gall-fly produces monstrous growths on the wild rose or oak-tree. Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed. When the views entertained in this volume on the origin of species, o~ when analogous views 11:re generally admitted, we can dimly foresee ~hat there will b~ a co~siderable revolution in natural history. Systematists will be able to pursue their labours as at present; but they will not be incessantly hau~ted by the sha~owy do"?-bt whether this or that form be 1n essence a speCies. This I feel sure, and I speak after experience, will be no slight relief. The endless disputes whether or J?-Ot s~me fifty species of British brambles are trl!e SJ>eCies w1ll .cea~e. Systematists will have only to decide (not that this w1ll be easy) whether any form be sufficiently co~s~ant and distinct from other forms, to be capable of defin1tlon ; and if definable whether the differences be sufficiently important to de;erve a specific name. This latter point will become a far more essential consideration than it is at |