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Show 98 DARWINISM CUAl'. peach is unknown in a wild state, unless it is clcrivocl from the common almond, on which point there is much difference of opinion among botanists and horticultnri. ts. Tho immense antiquity of most of our cultivated plants sufficiently explains the apparent n.hsonco of such useful productions in Australia and the Capo of Good Hope, notwithstanding that they both possess an exceedingly rich and varied flora.. Those countries having boon, 11ntil a comparatively recent period, inhabited only by nncivili od men, neither cultivation nor selection has boon carried on for a sufficiently long time. In North America, however, whore there was evidently a very ancient if low form of civilisation as indicated by tho remarkable mounds, oartlrwork, ancl other prehistoric remains, maize was cultivated, though it. was probably derived from Porn; and the ancio11t civilisation of that country and of Mexico has given rise to uo fewer than thirty-three useful cultivated plants. Conditions favourable to the production of Va1·iations. In order that plants n.nd animals may be improvocl ancl modified to any considerable extent, it is of comso essonti:tl that suitable variations . hould occur with tolcra.blo frcqnoney There seem to be three conditions which arc ospociaJly f<w ol{r able to tho production of variations : ( 1) That tho pa.rti ·nlar speci~s or variety should be kept .in very largo numbers; (2) that It should be spread over a Wide a.rca. a.nd tlm. snbjcd.ed to a .considerable divo~sity of physical conditions; ancl (:3) that It should be occa.swnally crossed with omo distinct lmt closely alli.od race. The first of those conditions is pcrlw pt> the most Important, the chance of variations of any p<trt icular kind being increased in proportion to tho qn:wti Ly of tho original stock and of its annual offspring. It has lJeCJI remarked that only those breed.ers who keep brgo Hocks <'an effect much improvement; and it is for tho same reason that pigeons and fowl., which can be so easily and r<tpidly increased, and which have been kept in such largo number. by so great a number of persons, have produced such stranrre and numerous varieties. In like manner, nurserymen who ~row frui t and flowers in large quantities have a great advantarro over })rivato . h b amateurs m t e production of new varieties. IV VARIATIO UNDER DOMESTTCATION 99 Althonrrh I believe, for reasons which wm b gi von fnrthor on, that ~some amount of variability i. a con ta.nt and nocos~mry property of all orga.ni. m , yet .t~orc app~a.n; to h uood ovillonco to show that chanuod. COil<htwn: of hfe t nd to increase it, both by a direct action on tho organisation aml hy indirectly affecting tho reproductive system.. I.Iencc the exton. ion of i viii. ation, by favouring d me. t10at1 n under altered conditions, facilib.tto: the proccs. of m <lification. Yet this chn.11u·c docs not seem to b an c .. cntial condition, for nowhere h<ts tho production of extreme varieties of phnt. and flo·wors been ca.rried farther than in Japan, whore carcfnl selection contirmocl for many rrcncmtions mu:t have lJ on the chief fn.ctor. Tho efT'oct of occa ·ionn I cross •: often resnl t: in a groat amount of varia,tion, hut it.nh;o leads to i1~:tahility of character and is therefore very l1ttle employed m tho production ~f fixed and well-marked races. F r this purpose, in fact, it h:ts to he '<trofnlly ~tvoidod, as it i. only hy isolation :1~1d pure brooding that any specially llcsirecl qnalitios Cttn he lll croascd by selection. It is for this r ·ason that :tmong savage peoples, whoso anirrmls rnn hn If wild, liLtle im1~r vem nt. t~~kos place ; twcl the difficulty of isol:tt.ion :tlso ·xpl:tms why ~]u;tm.ct and pure broods of cats arc so ra.rcly m 't w1th. Tho wHlo thsteibution of u ·oful animal an<l pl:tnts from a very r •mote epoch has, no donbt, boon a po,;orfnl cau ·~ of modification, bec:mso tho particul:tr breed first Introduced mto each country ha. often been kept pure for many years, and h:ts also hecn subjected to s]io·ht differences of conditions. 1t will :dso ustmlly hn.vo bee~ selected for a so~1~what different pmposo in each locality, and thus very distmct races would soon originate. . Tho important physiological effects of cro smg hr ods ?r stra.ins, a.nd the part this play. in tho economy of nature, w11l be oxpbined in a future chapter. Conchtding Remarks. The examples of v:tri;ttion now adclucocl-:--ancl those might have been :tlmost indefinitely incroased-w1ll suffice to ~how that thoro is hardly an organ or a quality in phnt. or annnn.ls which has not been observed to vary; and further, that wh 'llever any of those vari::ttion. have boo11 nsoful to man he has |