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Show SUMMARY ON VARIATION [0.A.AP. I. In the case of animals with separate sexes,, facility in preventing crosses is an important eleme~t of success in the formation of new races,-at least In a. country which is already stocked with other races. In_this respect enclosure of the land plays a part. Wandering savages or the inhabitants of open plains rarely possess more than one breed of the san1e species. Pigeons can b~ mated for life, and this is a great convenience to the f~nmer, f~r thus many races may be kept true, though mingled In the same aviary; and this circumstance ~ust have la:gely favoured the improvement and formatl~n of new breeds. Pigeons, I may add, can be pr_opa~ated.In great num.bers and at a very quick rate, and Inferior birds may be freely rejected, as ,vhen killed they serve for foo~. On ~he other hand cats from their nocturnal rambhng habits, cannot be ~atched, and, although so muc~ yalued by women and children we hardly ever see a drstrnct breed kept up ; such breeds as we do sometimes see are almost always imported from some other country, often fro~ islands. Although I do not doubt tha~ some domestic animals vary less than others, yet the ranty or absence of distinct breeds of the cat, the donkey, pea~ock, goose, &c., may be attributed in main part to selectro~ not haying been brought into play : in cats, from the drfi?.culty rn pairing them; in don_keys, from. only ~ few ber;r:g ~\:ept by poor people, and httle attent~on paid to t~eu breedino- · in peacocks from not berng very easily reared, an:a' a large stock ~ot kept; in geese, from being valuable only for two purposes, food ~nd feathers, ~nd mo;·e especially fron1 ito pleasure havrng been felt In the drsplay of distinct breeds. . To sum up on the origin of our Domestic .~aces of ~nl-mals and plants. I believe that the conditrons of hfe, from their action on the reproduc~ive sys~en;,, are so far of the highest impo:tal?-~e a_s ca~sing vanabihty .. I ~o not believe that vanabihty IS an 1nherent and necessar_y contingency, under all circumstances, with all organic beings as some authors have thought. The. effe~ts of variabllity are modified by various degrees of Inherrtance and of reversion. Variability is governed by 1nany un- CHAP. I.] UNDER DOMESTICATION. 45 known laws, more especially by that of correlation of growth. Something may be attributed to the direct action of the conditions of life. Something must be attributed to use and disuse. The final result is thus rendered infinitely complex. In some cases I do not doubt that the intercrossing of species, aboriginally distinct, has played an important part in the origin of our domestic productions. When in any country several domestic breeds have once ?een establi~hed, their occasional intercr?ssing, with the ard of select1on, has, no doubt, largely aided in the formfttion of new sub-breeds; but the importance of the crossing of varieties, has, I believe, been greatly exaggerated, both in regard to animals and to those plants which are propagated by seed. In plants which are temporarily propagated by cuttings, buds., &c., the importance of the crossing both of distinct species and of varieties is immense; for the cultivator here quite disregards the extreme variability both of hybrids and mongrels, and the frequent sterility of hybrids ; but the cases of plants not propagated by seed are of little importance to us, for their endurance is only temporary. Over all these causes of Change I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant Power. |