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Show 440 DARWINISM OIIAP. The Non-Heredity of Acqui1·ed Characters. Cert~tin observations on tho embry~logy of the lo:ver animals are held to afford direct proof of thts theory of hered1ty, but they arc too technical to be ma~lc clc~r to ?r.d~nary readers. A logical result of the theory 1s _the 1mposs1b1hty of the tmnsmis. ion of acquired character , smce. the n.wl?cular structure of the germ-plasm is already dctermmed Withm ~he embryo; and \V ci. mann holds that there .arc n.o facts whwh really prove that acquired characters can be mhc~1tcd, although their inheritn.nco has, by most writer , been considered so prob-able as hardly to stand in need of direct proof. . "\V c have already shown, in the earlier part o~ th1s. chapter, that many in tanccs of change, imputed t~ the ml~cntance of acquired variation , arc really cases of e~cct10n; '~h1le th.c very fact that use implies u:;ef~dne. s renders 1t almo t Impossible to eliminate the action of selection in a state of nature. As reo-arch mutilations, it is generally admitted that they are not he~cditary, and there i · ample evidence on this point. V\Then it wa the fashion to dock hor es' tails, it was not found that hor. es were horn with short tail ; nor arc Chinese women born with di ' totted feet; nor are any of the numerous forms of racial mutihtion in man, which have in some cases been carried on for hundreds of o·enerations, inherited. N everth clc s, a few cases of apparon~ inheritance of m~1~ilati?ns. hav ' been recorded 1 and these if tru tworthy, arc cbfficnltlCs m the way of the th~ory. 'I he' undoubtc~ inh~r~tancc of. di. cas_o is hardly a difficulty, hoc.;auso tho pred1spos1t10n to d1soa.so m ;t concronital not an acc1uired character, and as such '"ou1d be the subbj ect of ' inheritance. The often-quoted ca. o of a. c1 1' on.Ro induced by mutila.tion being inh 'ritod (Brown-Scquan~'s epileptic (fuine;t-picrs) has been discussed by Profes or \V Ol smann an~ hown ~o be not conclusive. Tho mutihttion its lf -a ~ection of certain nerves-was never inherited, but new forms. Again, in parthenogenetic females the complete apparatus for fertilisation re111aius umeduce(l; but if these varie(l ns do sexua.lly produ <·<·d anin1als, the orgau~; refened to, being unu~ed, would become. rn~~tm eutary: Even lllOre in1portant is the significance of the" p_olar hodte~, as explalnPd by Wei~n1ann in one of llis Es. nys; :ince, if l~is interpretati?n of them be correct, variability is a necessary consequence of sexual generatwn. J Darwin's Animals and Plants, vol. ii. pp. 23, 24. XI\' FUNDAMENTAL PROBLEM 441 tho rc~mlting epilepsy, or a general state of weakness, deformity, or sores, wa. sometimes inherited. It is, however, po ible that the mere injury introduced and encouraged the growth of certain microbes, which, spreading through the organism, sometimes reached the germ-cells, and thus transmitted a diseased condition to the offspring. ~ uch a tra.n ferone of microhcs is believed to occur in syphili and tuberculosis, and ha.s been ascertained to occur in the case of the muscardine silkworm di case.1 The Theo?'?J of Instinct. The theory now briofiy outlined cannot be said to be proved, hnt it commends itself to many physiologi ts as being inherently prohahle, and a. furnishing a good working hypotho is till c..lisphced by a bettor. "\V c cannot, therefore, accept any arguments a.gn.inst tho agency of natural selection which n.ro lm ·ed upon the oppo. ito and equally unproved theory that acquired characters are inherited; a.nd as this applies to the whole school of what may be termed N eoLamarckians, their speculations cease to have any weight. Tho same remark applies to the popnlar theory of instincts a being inherited habits; though Darwin gave very little woicrht to this, but derived almost all instincts from Bpontanoous useful variations which, like other spontaneous varia,tion , are of cont'. e inherited. At first ight it appear· a. if the acquired hn.bits of our trained dogs-pointer , retrievers, etc.-are certainly inherited; but thi · need not be tho case, because there must be some strncturn.l or psychical pc ·nliaritios, such as modifications in the atta.chmcnts of mw;clos, increased clolica.cy of smell or sin·ht, or peculiar like. and dislikes, which arc inherited; and from those, peculiar habits follow a. a natural co11 oquenco, or arc oa:ily acquired. Now, as selection has been con. tantly at work in improving all onr domestic animal , we have unconsciou.ly modified tho strnctmo, while preserving only those animals which best served our purpo ·o in their peculiar faculties, in. tincts, or ba.hits. 1 Jn his e:f>ay on "Heredity," Dr. W •ism ann di~cusses many other cases of Hnppose(l inheritance of acquired characters, and ~!tows that they can all be explained in other ways. Shortsightedness among civilised nations, for exalllple, is due partly to the absenc~ of selection and con ·equent rcgr e ~~ion towards a mean, and partly to it · iudividnal production by constant readlllg. |
