DARWINIAN THEORY 



688 



lv natnr.ilisis in tlicir classifications the high 



v.ilite -i -I ll|inil fiuistuiit anil prevalent Htructnies. 

 win-tiler these ! (if great or little use, or, as with 

 rudimentary organs, of none at all the wide 

 o|i|n)-itioii in value between such misleading re- 

 Henihlances of ii(lu|>tatii)ii, us, for instance, the fish- 

 like form of whales, and Midi characters of true 

 ullinity as are afforded by the structure of their 

 circulatory or respiratory system all these receive 

 a -imple ami natural explanation on the view of 

 the common descent of allied forms with modifica- 

 tion through variation and natural selection ; while 

 it is to be noted that no other explanation has ever 

 even l>een attempted. The element of descent, 

 too, is already used in linking all tho sexes, ages, 

 forms, and varieties of the same species, widely 

 though these (e.g. Cirripedes) may cliH'er from each 

 otliei in structure: and we have only to extend 

 it to understand the meaning and origin of the 

 Natural System. 



(b) JInHin/iiiff/. The members of the same class, 

 independently of their habits of life, resemble each 

 other in their general plan of organisation. Thus, 

 the hand of man, the digging-paw of the mole, the 

 leg of the horse, the paddle of the porpoise, and the 

 wing of the bat, are all constructed on the same 

 pattern, bone corresponding to bone. Similarly 

 with the hind-limb. Again, the mouths of insects 

 are of innumerable varieties of form and use 

 witness the long spiral trunk of a moth, and the 

 great jaws of a beetle yet these are formed by 

 modifications of an tipper lip, mandibles, and two 

 pairs of ma\ill.-e. Ana so it is with the limbs of 

 crustaceans, or the flowers of plants ; in fact, with 

 the organs of every class of beings. 



This conformity to type is ' powerfully suggestive 

 of true relationship, or inheritance from a common 

 ancestor;' it admits, in short, as no one indeed 

 denies, of a simple explanation in terms of the 

 evolutionary theory, and thus strengthens that 

 theory not a little. Attempts have been made to 

 explain this unity of plan in two other ways first, 

 by assuming it due to utility, which is negatived 

 by the facts, since organs of identical use (e.g. the 

 wings of a bird and those of a butterdy) very 

 frequently do not conform to the same type at all ; 

 secondly, by attributing it to a unity of design, 

 which, however, (a) instead of being always main- 

 tained, as it should be, on the theory, is not un- 

 frequently quite lost in highly specialised forms ; 

 and which, even if it always existed, (b) would 

 directly suggest the unity of descent, -the design 

 thus serving only to mislead the anatomist. 



Serial Homoloyy, too, has to be accounted for 

 that unity of type which is found on comparing the 

 different parts and organs in the same individual, 

 so that t lie wonderfully complex and varied jaws 

 and legs of a lobster, or the widely different leaves, 

 sepals, petals, stamens, and pistils of a flower, are 

 alt found to be modifications of a simple limb, and 

 a simple leaf -organ respectively. Isot only are 

 such metamorphoses apparent on comparison, but 

 they can be actually observed to occur during the 

 development of each individual; is then the term 

 metamorphosis to have a mere metaphorical mean- 

 ing when applied to the species, or has it not 

 actually arisen in past time, through the natural 

 selection and transmission of advantageous varia- 

 tions ? 



(c) Development. It has been already indicated 

 that the serially homologous parts in the same in- 

 dividual are alike during an early embryonic period, 

 as also are the homologous organs in animals which, 

 like bat, horse, and porpoise, may le widely differ- 

 entiated in adult life. So closely, too, do the 

 embryos of the most distinct species belonging to 

 the same class resemble each other, that even V on 

 Baer was unable to distinguish whether two un- 



148 



lalwlled specimens were lizard*, birds, or mammals. 

 This law of embryonic resemblance holds very 

 widely e.g. with young crustaceans. The embryo 

 often retains within the egg or womb structure* 

 which an- of no service to it, either at that or at a 

 later period of life, like the transitory gill-arches of 

 birds or mammals ; while, on the other hand, 

 larva- (e.g. of insects), which have to provide for 

 their own want*, undergo complete secondary 

 adaptation to the surrounding conditions. The 

 process of development goes from the general to 

 the special ; thus there is generally an advance in 

 organisation. In peculiar conditions, however, 

 degeneration may occur. All these facto are 

 readily explained on the principle of successive 

 slight variations not necessarily or generally super- 

 vening very early in life, and inherited at a corre- 

 s|K>nding period ; hence it is in the highest degree 

 probable tnat most embryonic stages show us more 

 or less completely the progenitor of the group in ito 

 adult state ; and embryology thus rises greatly in 

 interest. See EMBRYoLoGY. 



(d) Rudimentary Organs. Rudimentary, atro- 

 phied, and abortive organs, bearing the plain stamp 

 of inutility, are so extremely common that it is im- 

 possible to name a higher animal in which none 

 occurs. The mammae of male mammals, the hind- 

 legs of boas, the wings of many birds, or the teeth 

 of foetal whales, and the upper incisors of unborn 

 calves, are familiar instances. Such organs are in- 

 telligible on the evolutionary theory, and on that 

 theory alone. 



Recapitulation and Conclusion. After tersely 

 summing up the preceding moss of evidence, 

 Darwin concludes by pointing out (a) that the 

 theory of evolution by natural selection is no more 

 inimical to religion than is that of gravitation, to 

 which the same objection was strongly raised ; ( b ) 

 its revolutionary influence on the study of all de- 

 partments of natural history ; (c) on Psychology 

 (q.v.); (d) on the origin of man and his history 

 (see MAN ); (e) on our theories of future progress. 



Envoy. ' It is interesting to contemplate a 

 tangled bank clothed with many plants of many 

 kinds, with birds singing on the uushes, with vari- 

 ous insects flitting alout, and with worms crawling 

 through the damp earth, and to reflect that these 

 elaborately constructed forms, so different from 

 each other, and dependent on each other in so 

 complex a manner, have all been produced bv laws 

 I acting around us. These laws, taken in the largest 

 sense, being Growth with Reproduction ; and Inner- 

 itance, which is almost implied by reproduction ; 

 Variability from the indirect and direct action of 

 the conditions of life, and from use and disuse ; a 

 Ratio of Increase so high as to lead to a Struggle 

 for Life, and as a consequence to Natural Selec- 

 tion, entailing Divergence of Character and the 

 Extinction of less improved forms. Thus, from the 

 war of nature, from famine and death, the most 

 exalted object which we are capable of conceiving, 

 namely, the production of the higher animals, 

 directly follows. There is grandeur in this view of 

 life, with its several powers, having been originally 

 breathed bv the Creator into a few forms, or into 

 one; and that, whilst this planet has jjone cycling 

 on according to the fixed law of gravity, from so 

 simple a Wginning endless forms most l>eautiful 

 and most wonderful have been, and are being, 

 evolved.' 



The stormy reception of the Origin ofSjKcics, the 

 controversies to which it gave rise, ita rapid 

 and widespread acceptance, helped as it was ny. 

 the indeiiendent support, yet generous self-abnega- 

 tion. of Mr Wallace, and the jiowerful advocacy of 

 Huxley, Hooker, Asa Grav, and others, are all 

 recorded in Darwin's Life. Of the proposed expan- 

 sion of the Origin, only the first chapter actually 



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