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Show CH.AP. I. 42 SUMMARY ON VARIATION crossing with distinct species) those many admir~bl~ varieties of the strawberry which have been raise during the last thirty or forty years. f: 'lit In the case of animals with separate sexes, aCI y in preventing crosses is an important elem~nt of success in the formation of new races,-at least, In a co:Intry which is already stocked with other races. In this .re-s ect enclosure of the land plays a part. W andenng s~vages or the inhabitants of open pl~ins rar~ly possess more than one breed of the same species. ~Igeons can be mated for life, and this is a great convenience to the fancier for thus many races may be kept true, though mingled in the same aviary; and this circumstance m~st have largely favoured the improvement and formatiOn of new breeds. Pigeons, I may add, can be pro~agat.ed in great numbers and at a very quick r~te, and InferiOr birds may be freely rejected, as when killed they serve for food. On the other hand, cats, from their nocturnal rambling habits, cannot be matched, and, although so much valued by women and children, we hardly ever see a distinct breed kept up ; such breeds as we do sometimes see are almost always imported from some other country, often from islands. Although I do not doubt that some domestic animals vary less than others, yet the rarity or absence of distinct breeds of the cat, the donkey, peacock, goose, &c., may be attribute~ in main part to selection not having been brought In~o play : in cats, from the difficulty in pairing them ; In donkeys, from only a few being kept by poor people, and little attention paid to their breeding ; in peacocks, from not being very easily reared and a large stock not kept ; in geese, from being valuable only for two purposes, food and feathers, and more especially from no pleasure having been felt in the display of distinct breeds. CH.AP.I. UNDER DOMESTICATION. 43 To sum up on the origin of our Domestic Races of animals and plants. I believe that the conditions of life, from their action on the reproductive system, are so far of the ~ighest importance as causing variability. I do not beheve that variability is an inherent and necess.a ry contingency, under all circumstances ' with all organiC beings, as some authors have thought. The ?ffect~ of variability are modified by various degrees of Inheritance and of reversion. Variability is governed by ~any unknown laws, more especially by that of correlatiOn of growth. Something may be attributed to the direct ac.tion of the conditions of life. Something must be attnbuted to use and disuse. The final result is thus rendered infinitely complex. In some cases, I do no~ ~oubt that the intercrossing of species, aboriginally distinct, has played an important part in the origin of our domesti: productions. When in any country several domestic breeds have once been established their occasional intercrossing, with the aid of selection: has, no doubt, largely aided in the formation of new sub-breeds; but the importance of the crossing of ;arieties 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 pro, pagated 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 proragated by seed are of little importance to us, for thmr 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. |