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Show CHAP. VI. ON THEORY. 194 DIFFICULTIES . . t" so natura1 selection, worlnngf the very same Inven wn, in and taking advan~age o for the good of each be g t"m.es modified In very . . has some I . b . analogous variations, ts in two organic mngs, r two par t nearly the same ~anne heir structure in common o which owe but httle :.: ancestor. inheritance from the sa "t ·s roost difficult to con- Although I.n many cases I o1 rgan could have arri·v e d "tions an · J. ecture by what transi "dering that the proportion t t . yet consi k at its present s a e ' ' t the extinct and un nown . . d k wn forms o 1 of hving an no b astonished how rare y an ll I have een . . l is very sma ' ds which no transitiOna b m.ed towar k · organ can e na 1 'd The truth of this remar IS grade is known to h ~a id canon in natural h~story _of indeed shown bY: t a 0 , We meet with this admis" Natura non faCit saltuf ml. st every experienced natu- . h . t" gs o a roo d . sion In t e wri In. Ed ds has well expresse It, . Milne war . . . ralist ; or, as. . . et but niggard m InnovatiOn. nature is prodigal In va~I Jr~ation should this be so? Why, on the theory o t and o~gans of many indeWhy should all the pars d to have been separately Pendent beings, each supl pos~ ature be so invarfably created 1.i.' 0r I't s pro per p ace md nt ? ' Why should not h b graduate s eps ? linked toget er y 1 from structure to structure . Nature have taken a eap 1 1 cti"on we can clearly h of natura se e ' · On the t eory uld t. for natural selectiOn understand why she sho d n~ ' of slight successive can act only by taking a v:~ age leap but must ad-variations ; she can never a e a ' vance by the shortest and slowest steps. . t importanee.-As natural Organs of bttle apparen h b the preservation of selection acts by life and deat ,- y . t"on and by the individuals with any favourable £variura albl~ deviation of destructi.O n of t h ose WI' th a. ny un avo h difficulty I·l l structure,-! h ave som et1mes felt roue CHAP. VI. OHGANS OF LITTLE IMPORTANCE. 195 understanding the origin of simple parts, of which the 1'1<.- 1 ., : ,( importance does not seem sufficient to cause the preser- evi.u~v 1 vation of successively varying individuals. I have some- ~ ... · J times felt as much difficulty, though of a very different /' · kind, on this head, as in the case of an organ as perfect and complex as the eye. In the :first place, we are much too ignorant in regard to the whole economy of any one organic being, to say what slight modifications would be of importance or not. In a former chapter I have given instances of most trifling characters, such as the down on fruit and the colour of the flesh, which, from determining the attacks of insects or from being correlated with constitutional differences, might assuredly be acted on by natural selection. The tail of the giraffe looks like an artificially constructed fly-flapper; and it seems at first incredible that this could have been adapted for its present purpose by successive slight modifications, each better and better, for so trifling an object as driving away flies; yet we should pause before being too positive even in this case, for we know that the distribution and existence of cattle and other animals in South America absolutely depends on their power of resisting the attacks of insects: so that individuals which could by any means defend themselves from these small enemies, would be able to range into new pastures and thus gain a great advantage. It is not that the larger quadrupeds are actually destroyed (except in some rare cas~s) by the flies, but they are incessantly harassed and t~e1r strength reduced, so that they are more subject to disease, or not so well enabled in a coming dearth to search for food, or to escape from beasts of prey. Organs now of trifling importance have probably in sorn_e cases been of high importance to an early progenitor, and, after having been slowly perfected at a K2 |
