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Show DARWINISM CHAP. produce fertile individuals, and which reproduce themselves by o·enorn.tion, in such a manner thl1t we may from analogy sup7)ose them all to have sprung from one single individual." And the zoologist Swainson gives a somewhat similar definition : "A species, in the usual acceptation of the term, is an animal which, in a state of nature, is distinguished by certain peculiarities of form, size, colour, or other circumstances, from another animal. It propagates, 'after its kind,' inuividuals perfectly resembling tho parent; its peculiarities, therefore, arc permanent." 1 To illustrate these definitions we will take two common English birds, the rook (Corvus frugilegus) and tho crow (Corvus c01·one). These arc distinct species, because, in the first place, they always differ from each other in certain slight peculiarities of structure, form, and habits, and, in the second place, because rooks always produce rooks, and crows prouuce crows, and they do not interbreed. It was therefore concluded that all the rooks in the world hacl descended from a single pair of rooks, and the crows in like manner from <t single pair of crows, while it was considered impossible that crows could have descended from rooks or vice versa. The ''origin" of the fir t pair of each kind was a mystery. Similar remarks may be applied to our two common plan ts, the sweet violet (Viola odorata) and the dog violet (Viola. canina). These also produce their like and never produce each other or intermingle, and they were therefore each supposed to have sprung from a single individual whose "origin" was unknown. But besides the crow and the rook there are about thirty other kinds of birds in various parts of the world, all so much like our species that they receive the common name of crows ; and some of them differ less from each other than docs om crow from our rook These arc all species of the genus Corvus, and were therefore believed to have been always as distinct as they are now, neither more nor less, and to have each descended from one pair of ::~n ces· tral crows of the same identical species, which themselves had an unknown "origin." Of violets there are more than a. h~nd:ed differe~t kinds in vnrious parts of the world, all <hffenng very slightly from each other and formin(J' distinct b 1 Geography and Olctss-ijication of A m'm,als, p. 350. WHAT ARE SPECIES 3 spec.ies _of the genus ~iola. . But, as these also each produce thc1r hke and do not mtermmgle, it was believed that every one of them had always been as distinct from all the others as it is now, that all the individuals of each kind had descended from one ancestor, but that the " origin " of these hundred slightly differing ancestors was unknown. In the words of Sir ,John Herschel, quoted by Mr. Darwin, the origin of such species was "the mystery of mysteries." · The Early Tmnsmutationists. A few great naturalists, struck by the very slight difference between many of these species, and the numerous links that exist between th.e most different forms of animals and plants, a~d also .obscr~mg that a great many species do vary consHlerably m their forms, colours, and habits, conceived the idea that they might be all produced one from the other. The most eminent of these writers was a great French naturalist, ~ama~ck, ~ho p~blished an elaborate work, the Philosophie Zoologtque, m whiCh he endeavoured to prove that all animals whatever arc descended from other species of animals. He attributed the change of species chiefly to the effect of changes in the conditions of life-such as climate, food, etc.and especially to the desires and efforts of the animals themselves to improve their condition, leading to a modification of form or size in certain parts, owing to the well-known physiolog~ cal law that a1l organs are strengthened by constant use, wh1lc they are weakened or even completely lost by disuse. The arguments of Lamarck did not, however, satisfy naturalists, and though a few adopted the view th~t closely allied species had descended from each other, the general belief of the educated public was, that each species was a" special creation" quite independent of all others; while the great body of naturalists equally held, that the change from one species to another by any known law or cause was impossible, and that the " origin of species " was an unsolved and probably insoluble problem. The only other important work deali~g with. the question was the celebrated Vestiges of C1·eatwn, pubh.shed anonymously, but now acknowledged to have been wnttcn by the late Robert Chambers. In thi work the action of general laws was traced throughout the |
