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Show 132 DARWINISM OTIAJ>, unimportant for the welfare of the ~pecie~, they may be, and apparently often have bc~n, tran.smitted m ncar~! th~ ~am e state to numermts, otherwzse modified, descendants ( Ortgm, p. 175). The words I have here italicised clearly show that such chamcters arc usually not "specific," in the sense thaL they are such as distinguish species from each other, but are found in numerous allied species. Again : " Thus a largt~ yet undefined extension may safely be given to the direct and indirect results of natural selection; but I now admit, aft('!' readina the essay of Niigcli on plants, and the remarks hy variou~ authors with ro poet to anim~Lls, more especially thos<) recently made by Professor Broca, that in the earlier editi on.· of my Origin of Species I perhaps attributed too much to the action of natural selection or the survival of tho fittest. I have altered tho fifth edition of the Origin so as to confine my remarks to adaptive changes of structure, but I am conrincnl, from the light gained during even the last jew yea1·s, tlwt 'CI!1'.'J many structures which now appear to us useless, will hereajte1· /1c JHoved to be useful, and will therefore come within the mnge rlj' nat'ltml selection. Nevertheless I did not formerly consicl 'r sufficiently the existence of structures which, as fa'r as we wn rtf present judge, are neither beneficial nor injurious; and thi: 1 believe to be one of the greatest oversights as yet detected in my work." Now it is to be remarked that neither in these passages nor in any of the other less distinct expressions of opinion on this question, does Darwin ever admit that "specific characters "-that is, the particular characters which serve to distinguish one species from another-are ever useless, much less that "a large proportion of them" are so, as Mr. Roman o~ makes him "freely acknowledge." On the other hand, in the passage which I have italicised he. strongly expressc. hi~ view that much of what we suppose to be useless is due to our ignorance; and as I hold myself that, as regards many of the supposed useless characters, this is the true explanation, it may be well to give a brief sketch of the progress of knowledge in transferring characters from the one category to the other. We have only to go back a single generation, and not even the most acute botanist could have sugaestcd a reasomLb1e nsc, for each species of plant, of the infinitely varied forms, sizes, VI DIFFICULTIES AND on.m TIO S 133 and colours of the flowers, the shapes and arrangement of the leaves, and the numerous other external characters of the whole plant. But since Mr. Darwin showed that plants gained both in vigour and in fertility by beino· crossed with other individuals of the same species, and that this crossing was usually effected by insects which, in search of nectar or pollen, carried the pollen from one plant to the flowers of another plant, almost every dctaH is found to have a purpo. e and a use. The shape, the size, ami the colour of the petal. , even the streaks and spots with which they are adorned tho position in which they stand, the movements of tho sta~ens and pistil at various times, especially at tho period of, and just after, fertilisation, have been proved to be strictly adaptive in so many cases that botanists now believe that all the external characters of flowers either are or have been of use to the species. It has also been shown, by Kerner and other botanists, that .another set of characteristics have relation to the preventiOn of ants, slugs, and other animnJs from reaching the flowers, because these creatures would devour or injure them without effecting fertilisation. The spines, hairs, or sticky glands on the stem or flower- talk, the curious hairs or processes shutting up tho flower, or sometimes even the extreme smoothness and polish of the outside of the petals so that few insects can hang to the part, have been shown ~o be related to the possible intrusion of these "unbidden guests." 1 And, still more recently, attempts have been made by Grant Allen and Sir John Lubbock to account for the innumerable forms, textures, and groupings of leaves, by their relation to the needs of the plants themselves ; and there can be little doupt that these attempts will be ultimately successful. Again, just as flowers have been adapted to secure fertilisation or cross-fertili ation fruits have been developed to assist in the dispersal of seeds ; and their forms, sizes, juices, and colours can be shown to be SJ?ecially adapted to secure such dispersal by the agency of b1rds and mammals ; while the same end is secured in other 1 See Kerner's Flowers and thei1· Unbidden Guests for numerous other structures and peculiarities of plants which arc shown to be adaptive and useful. |