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Show CHAPTER VI DIFFICULTIES AND OBJECTIONS Difficulty as to smallness of variations-As to tho right variations occurring when required- Tho beginnings of important orgaus-The mammary glands-Tho eyes of flatfish- Origin of tho oyc- Usclo s or non-adaptive characters-Recent extension of tho region of utility in plants-The same in animals-Uses of tails- Of the homs of doerOf the scale-ornamentation of roptiics- Instability of non-adaptive charactcrs-Dclbccufs law-No "specific'' character proved to be useless-The swamping effects of intcrcrossing--Isolation as prcvCJiting intercrossing- Gulick on the effects of isolation-Cases in which isolation is ineffective. IN the present chapter I propose to discuss the more obvious anJ often repeated objections to Darwin's theory, and to show how fa.r they affect its character as a true and sufficient explanation of the origin of species. The more recondite difficulties, affecting such fundamental questions as the causes and laws of variability, will be left for a future chapter, after we have become better acquainted with the applications of tho theory to the more important adaptations and correlations of animal and plant life. O~e of the earliest and most often repeated objections was, ~hat _1t wa~ di~cul~ "to imagine a reason why variations tendmg m an mfimtes1mal degree in any special direction should ~e yreserve~," or to believe that tho complex adaptation of hvmg orgamsms could have been produced "by infinitesimal beginnings." ~~w this term "infinitesimal," used by a wellknown early cntiC of the Origin of Specie~, was never made use of by Darwin himself, who spoke only of variations beina "slight," and of the_"srn~ll amount" of the variations that might be selected. Even m usmg these terms he un<loubtodly afforded .. CHAP. VI DIFFICULTIES AND OBJECTIONS 127 grounds for tho objection above made, that such small and slight variations could be of no real use, and would not Jetermine the survival of the individuals possessing them. W o have seen, however, in our third chapter, that even Danrin's terms were hardly justified; and that the variability of many important species is of considerable amount, and may very often be properly described as large. As this is found to be the case both in animals and plants, and in all their chief groups and subdivisions, and also to apply to all the separate parts and oraans that have been compared, we must take it as proved 0 that the average amount of v_ariability presents. no difficulty whatever in the way of tho actiOn of natural selectiOn. It may be here mentioned that, up to the time of tho preparation of the last edition of 1'he Origin of Species, Darwin had not seen tho work of Mr. J. A. Allen of Harvard University (then only just publishoJ), which gave us the firs~ body _of accurate comparisons and measurements de~onstratmg t?1s largo amount of variability. Since then evidence of th1s nature has been accumulating, and we are, therefore, now in a far better position to appreciate tho fa~iliti~s for natural selection, in this respect, than was Mr. Darwm himself. Another objection of a similar nature is, that tho chances are immensely against the right variation or c9mbination of variations occurring just when required; and further, that no variation can be perpetuated that is not accompanied by several concomitant variations of dependent parts-greater lenath of a wina in a bird, for example, would be of little usc if ubn accompaniebd by increased volume or contract!" l"1 ty of t h e muscles which move it. This objection seemed a very strong one so long as it was supposed tha.t variations occurred si~gly and at considerable intervals; but it ceases to have any weight now we know that they occur simultaneously in various parts of the oraanism, and also in a large proportion of the individuals ~hich make up the species. A considerable nn~ her of individuals will therefore, every year possess the reqmred combination of characters; and it may also be considered probable that when the two characters are such that they always act together, there will be such a correlation betwee_n them that they will frequently va1·y together. ~ut ~he_re Is another consideration that seems to show that th1s comc1dent |