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Show I 14.8 DARWINISM CHAP. . c ual distance apart. In a very another on the same sJde an hq L' I1ean Society last year, on ted to t e 1 lcnathy paper, prescn 1 C n ulative Sca:rcgatw· n, " M I·. "Doiv eracnt E vo 1u t.w n throuror 1 uhm' views in'"' to <t comp l c t c o , t vork out rs . . 1 1 Gulick cndeavoms o ' . h perhaps he m hcatcc )y · · t of whlC may · theory ' the. mam pom . " No two pOI· t'ons of a spcc1cs pos. cs. 1 . the followmg passage · t , and the initial chffercnces exactly the same avera gc charac c. r, rnent and on each ot1 H ' r . a the envrron . are for ever reactmo on . e sing di vcro·cnce m C;te1 1 to ensure mer a o h in such. a way ats' on as 1o ng as the individuals of t c two SUCCCSSlVe genera l <' • "l f , intcrcrossma. · 1 groups are kept rom . h t thoe views of Mr. Darwm anc It need hardl;y be sm~l ~ t~e notion that, if the cnvironm 'nt myself are inconsl~tc~t w~t th two isolated portions of the were absolutely simJbr or a~d constant divergence would species, any such. ncces::~r to assume that what seem to take place. It Is. ~n arc really identical to such snHt1l us identical condltl.ons < th lancl molluscs of whose . msms as esc ' ' . and dehcate orga h ssive staac of their cx1stcnce, needs and difficulti~s at eac s~ccethe adult animn1, we arc so from the fr~shly-laid e?fh:~xa~t proportions of .the variou:-; profoundly Ignorant. b of each kind of m:ect or of species of plan~s, ~~e n~m m~~ or less exposure to sunshine bird the pccuhantlCs ? . . 1 h and other . li uht ' . d t rtam cntica cpoc s, < o or. to wm ha · ch cet o us arc a bsolutely immaterial a.nd hu n-d1fferences w 1 . bl m'1Y he of tl1 e hr· o(/ ho.s t si o(/ nificancc .t o t esc rccogmsa e, . , be uite sufficient to rcqmrc some humble creatmcs, and . \ or colour whi ch nn.tt~ral slight adju~tmen.ts of slze, ~;r' c know 'of the h .cts of selection w1ll brmg ab~ur tha.; without this action of variation lca~s us to . 0 1~~\ r~ducccl over the whole area natural selectiOn, there '~ou. c c_ p lccl too·ethcr Jlot a distinct . f · tant vanct1es mmg o ' a senes ~ moons h confined to its own ]imi tecl_area. segregatiOn of_forms eac h t in the di stributlOn and Mr. Da.rwm ha~ shown .t l a '. l is of more importance modification of species, t_hc bio oflC~hc strurralc with other than the physical cnvJronmcn ' h th l:twith the forces . b . rr often more severe t an a orgamsms mno . 1 .d t ·n the case of plnnts, of natur<::. This is partJCular yl ef:I en o:Upctition thrive in a many of which, when protectc< rom c ' . z l vol xx p. 215. 1 Joumal of the Linnean Soctety, oo ogy, . . VI DIFFICULTIES AND OBJEU'l'IONS 149 soil, climate, and atmosphere widely different from those of their native habitat. Thus, many alpine plants only found near perpetual snow thrive well in our gardens at the level of the sea; as do the tritomas from the sultry plains of South Africa, the yuccas from the arid hills of Texas and Mexico, and the fuchsias from the damp and dreary shores of the Straits of Magelhn. It has been well said that plants do not live where they like, but where they can; and the same remark will apply to the animal world. Horses and cattle run wild and thrive both in North and South America; rabbits, once confined to the south of Europe, have established themselves in our own country and in Australia; while the domestic fowl, a. native of tropical India, thrives well in every part of the temperate zone. If, then, we admit that when one portion of a species is separated from the rest, there will ncce. sa.rily be a slight difference in tho average characters of the two portions, it docs not follow that this difference has much if any cfl'ect upon the characteristics that are developed by a long period of isolation. In tho first place, the difference itself will necessarily be very slight unless there is an exceptional amount of variability in the species; and in the next place, if the average characters of the species arc the expression of its exact adaptation to its whole environment, then, given a precisely similar environment, and the isolated portion will inevitably be brought back to tho same average of characters. But, as a matter of fact, it is impossible that tho environment of the isolated portion can be ex:wtly like that of the bulk of the species. It cannot be so phy ·ically, since no two separated areas can be absolutely alike in climate and soil; and oven if these are the same, the geographical features, size, contour, and relation to winds, seas, and rivers, would certainly differ. Biologically, the differences arc sure to be considorn blc. The isolated portion of a species will almost always be in a much smaller area than that occupied by the species as a whole, hence it is at once in a different position as regards its own kind. The proportions of all the other species of animals aud plants are also sure to differ in the two areas, and some species will almost always be absent in the smaller which arc present in the larger country. Those differences will act and react on |