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Show (CHAP. V. LAWS OF VARIATION. 144 . . d t the same constitution an inherited from a. c~mmonhpar:~ed on by sin1ilar unknown tendency to variation, w hle kinO'dom we have a case of influences. I~ t~e v~geta lar ~d stems, or roots as comanalogous variatlon, Sn t~~ ~tur~ip and Rutabaga, plants monly called, of the . we IS k as varieties produced by cuiwhich several botanists ran t. if this be not so, the case tivation from a comnlon {aren ~ariation in two so-called will then be _one of ana o~~us e a third may be added, distinct . speCies; an~ to. esA.ccording to the ordinary namely, the com~n urn;p. been independently created, view of each speCie~l;f;~~! this similarity in the enlarged we should have to a ot to the vera causa of comstem~ of these three piant~o~sequent tendency to vary in ma luinkeit y1 noafn dneesrc, ebnut,t aton t:r ee separate yet closely related acts of creation. h ve another case, namely, With pigeons, however, .we 11 ~he breeds of slaty-blue the occasional appearance In ~he win s a ~hite rump, a birds with two ~la~k tb;rs .:fth the otl~e~ feathers externalbar at the end o t .e bal ' 'th white As all these re- I d ed near thmr ases w1 · . I Y e g · · f the parent rock-pigeon, premarks are character~fr!.d o bt that this is a case of rever-sume that no one WI ~~ analo ous variation appearing sion, and notl obf a dew ~ e may¥ think confidently come in the severa ree s. have seen these to this conclusion, be~aus~i a~ia~~e to appear 'in the coloured ffiar~s arf t e~I~~~iJct and differently coloured cross;d o TI:fhfs c~e there is nothing in the external ~~!~i:i~n~n of life to c 1 ausetkh e {eappJa~h~i~ff!e~~: ~}at~~ blue with the s.evera mar s, eyof~ h "t mere' act of cr~ss·~ ng on the laws. o· 1n faecr1t atnhcaet. characters N 0 doubt 1t 1s a very surpr1s1n~ . s should reappear after h_aving been ohst forbmanl h~~I~:rn £ h d d f eneratlons But w en a ree or un re s o g · h b d the o:ffsprin 0' oc-crossed only once by ~orne o; e~ve~~ei~ character t~ the casionally show a ten ency ot; some say for a dozen £ · b d for many genera 1ons- ' . oorr mevgenn ar esec ore of generat ' s After twelve generatwns, lOll • ·on of the proportion of blood, to use a common expressi ' CnAP, V.] LAWS OF VARIATION. 145 any one ancestor, is only 1 in 2048; and yet, as we see, it is gener~lly believed that a tendency to reversion is retained by this very small proportion of foreign blood. In a breed which has not been crossed, but in which both parents have lost some character which their progenitor possessed, the tendency, whether strong or weak, to reproduce the lost character might be, as was formerly remarked, for all that we can see to the contra,ry, transmitted for almost any number of generations. When a character which has been lost in a breed, reappears after a great number of generations, the most probable hypothesis is, not that the offspring suddenly takes after an ancestor some hundred generations distant, but that in each successive generation there has been a tendency to reproduce the character in question, which at last, under ·unknown favourable conditions, gain~ an ascendancy. For instance, it is probable that in each generation of the barb-pigeon, which produces most rarely a blue and black-barred bird, there has been a tendency in each generation in the plumage to assume this colour. This vie·w· is hypothetical, but could be supported by some facts ; and I can see no more abstract improbability in a tendency to produce any character being inherited for an endless number of generations, than in quite useless or rudimentary organs being, as we all know them to be, thus inherited. Indeed, we may sometimes observe a mere tendency to produce a rudiment inherited: for instance, in the com1non snap-dragon (Antirrhinum) a rudiment of a fifth stamen so often appears, that th1s plant must have an inherited tendency to produce it. As all the species of the same genus are supposed, on my theory, to have descended from a common parent, it might be expected that they would occasionally vary in an analogous manner; so that a variety of one species would resemble in some of its characters another species ; this other species being on my view only a well-marked and permanent variety. But characters thus gained would probably be of an unimportant nature, for the presence of all important characters will be governed by natural selection, in accordance with the diverse habits of 7 |