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Show --~ -- 160 DARWINISM ,, .;;; CllAP. has received <1eci~i vc evidence that the hybrids between these ~Lrc perfectly fertile inter se. . Doo·s ha.vc been frequently crossed with wolves and Wl.th jaclml;, and their hy Lriu offspring ha v? been found to be. fertile inter se to the third or fourth genemtwn, .and .then u. ually to show some signs of sterility or of dete~'Ioratwn. ~he wo~f and dog may be originally the same spec!c.-, b~l~ the p ckal 1s certa.inly distinct; and the appcantnc~ of mfert1bty or~ of wca~~ncs. is probably due to the fact th~t, m almost all the~c cxpcu-men t s, the oflsprin•or of a sin<.oY le pau.· - thcmsc· lvo1s u ually f·r om, the same litter-were bred m-and-m, and th1s a one som~tlm~s produces the most deleterious effects. Thus, Mr. Low n~ ~1 s great work on the Do1nestiw~ed Aninutls of Orertt /Jr~ta111.' says : "If we shall breed. a pa1r o~ do~s from the sa~c htt~1, and unite aga.i 11 the offsprmg of th ts pa1r, we shall. p1 oduce a.t once a feeble race of creatures ; and the process bemg rcpea.ted for one or two generations more, the family will die out, or he incapable of proparratina their race. A gentleman of Scotland made the cxpcrim~1t o~ a large scale with certain foxhounds, and he found that the race actually became monstrous and perished utterly." The same writer tells us that ho~s have been made the subject of similar experiments: "After a few aenerations the victims manifest the change induced in tho syste0m. They become of diminished size ; the bri 'tles arc changed into hairs; the limbs be~ome feeble and short; the litters diminish in frequency, and m the number of the you11g produced ; the mother becomes unable to nouris~ them, an<l, if the experiment be carried as far. as .the ca.sc wil~ allow, Lh~ feeble, and frequently mons~rous oflsprmg,. will be m cap~bl~, ~f being reared up, and the miserable race w1ll utterly pensh: . These precise statement , by one of the greatest authont•cs on our domesticated animals, are sufficient to show that Lhe fact of infertility or degeneracy appearing in the offspring of hybrids after a few generations need not be imputed to the fact of the first parents being distinct species, ·incc exactly t!1e smne phenomena appear when indivi.d~als of the ?:tme . pcc1es arc bred uncler simibr adverse conditiOns. But m almost all the experiments that have hitherto been ma~e in cro. sing distinct species, no care has been taken to avmd close mtcr- 1 Low's Dumesticctle,z Animals of Grectt Brilu'in, Introductiou, p. lxi\'. VII ON TilE INFERTILITY OF CROSSES 161 breeding by securing several hybrids from quite distinct stocks to s~art with, and by having two or more sets .of experiments c:1rned on at once, so that crosses between the hybrids produ.ced may be occasionally made. Till this is done no expcnmc~ts, sue~ as those hitherto tried, can be held to prove that hybnds arc m all cases infertile inter se. . . It h~s, however, b~~n denie~l by Mr. A. H. Huth, in his ~ntercstmg worl~ or~ 'lhe .M~m:~a~e of Near Kin, that any .tmour~t of brccdmg m-and-m 1s m 1tsclf hurtful; and he quotes the cv1dcnce of numerous breeders whose choicest stocks have always been so bred, as well as cases like the Porto Santo ra?bits, the goats of Juan Fernandez, and other cases in which n.m~als" all~wed to run wild have increased prodigiously and contmucd m perfect health and virrour althouo·h all derived f . 1 b ' b rom a smg c p:1ir. But ill all these cases there has been rigid selection by which the weak or the iufcrtilc have been eliminated, and with such selection there is no doubt that the i~l effects of ~lose intcrbrecdi ng can be proven ted for a long time; but th1s by n~ means proves that no ill effects are prou~ ccd. ~r. Ruth lum~elf quotes M. Alli(~, M. Aubc\, Stephens, G~blett, ~1r John Scbnght, Y ouatt, Druce, Lord \V cston, and ?ther emi~cnt breeders, as finding from experience that close mterbreedmg does produce bad effects ; and it cannot be suppo~ed t~at .there wo~ld be such a consensus of opinion on th1s pomt If the ev1l were altogether imaginary. Mr. Ruth argues, that the evil results which do occur do not ~epcnu on the close interbreeding itself, but on the tendency 1t has to perpetuate any constitutional weakness or other hereditary ta~nts; and h~ attempts to prove this by the argument that "1f crosses act by virtue of bcinrr a cross and not bf virtue of removing an hereditary taint, then the g;eater the d1:fferencc between the two animals crossed the more beneficial will that act be." He then shows that, the wider the difference the less is the benefit, and concludes that a cross as such has no beneficial effect. A parallel argument would b~ that ch~nrrc of air, as from inland to the sea-coast or from ' a low to ~n elevated si~e, is not beneficial in itself, because, if so, a change to the tropics or to the polar regions should be more beneficial. In both these cases it may well be that no bencfi t would accrue to a person in perfect health; but then there is no M |
